m.l. report no. 882 - slac.stanford.edu · high-power waveguide components ... 2. coupler geometry...
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M-291
e
LINEAR ELECTRON ACCELERATOR STUDIES
A.E.C. Contract AT(04-3)-21 (Project Agreement No. 1)
Final Report
M.L. Report No. 882 M Report No. 291
December 1961
Stanford Linear Accelerator Center Stanford University Stanford, Cal i forn ia
Proprietory data of Stanford University and/or U. S . Atomic Energy
Recipient hereby agrees not t o publish the within informa- Commission.
t i o n without spec i f i c permission of Stanford University.
Nothing i n t h i s permission s h a l l be construed as a warranty or representa t ion by o r on behalf of Stanford University and/or t h e United
S t a t e s Government t h a t exercise of t he permission o r r i g h t s herein
granted w i l l not in f r inge patent , copyright, trademark o r o ther r i g h t s
of t h i r d p a r t i e s nor s h a l l Stanford University and/or t h e Government
bear any l i a b i l i t y o r r e spons ib i l i t y f o r any such infringement.
No l i c e n s e s o r o ther r i g h t s under pa ten ts o r with respect t o
trademarks o r t r ade names a re herein granted by implication, es toppel
o r otherwise and no l i censes o r o ther r i g h t s respect ing t r ade secre ts ,
unpatented processes, ideas or devices or t o use any copyrighted
material are here in granted by implication, es toppel o r otherwise
except t o t h e ex ten t revealed by t h e technica l d a t a and information,
t he subjec t of t h e permission herein granted.
I . I1 . I11 .
Iv .
V .
VI .
VI1 0
VI11 .
TABLE OF CON!TENTS
Page Introduct ion . . . . . . . . . . . . . . . . . . . . . . . 2
Mark IVprogram . . . . . . . . . . . . . . . . . . . . . 3 Accelerator s t ruc tu re and high-power waveguide
component s tud ie s . . . . . . . . . . . . . . . . . . . . 5 A . Radiofrequency s tudies of t he acce lera tor s t ruc tu re . 5 B . Electroforming . . . . . . . . . . . . . . . . . . . . 12
C . Brazing . . . . . . . . . . . . . . . . . . . . . . . 12
D . Water jacket . . . . . . . . . . . . . . . . . . . . . 13 E . High-power waveguide components . . . . . . . . . . . 1 4 In j ec t ion system . . . . . . . . . . . . . . . . . . . . . 15 A . Mark IV conversion program . . . . . . . . . . . . . . 15 B . Comparison of two bas i c ty-pes of i n j e c t o r s . . . 15 C . G u n spec i f i ca t ions . . . . . . . . . . . . . . . . . . 15 D . Two-element buncher . . . . . . . . . . . . . . . . . 13 Microwave c i r c u i t s . . . . . . . . . . . . . . . . . . . . 17 A . General rf s tud ie s . . . . . . . . . . . . . . . . . . 17 B . Drive system . . . . . . . . . . . . . . . . . . . . . 24
c . Phasing system . . . . . . . . . . . . . . . . . . . . 26 Klystron s tudies . . . . . . . . . . . . . . . . . . . . . 31 A . Tube complement and performance . . . . . . . . . . . 31 B . Research and development subcontracts . . . . . . . . 32 C . New f a c i l i t i e s . . . . . . . . . . . . . . . . . . . . 32 D . Life tes ts . . . . . . . . . . . . . . . . . . . . . . 33 E . Experimental tubes . . . . . . . . . . . . . . . . . . 34 F . Planning the klystron procurement . . . . . . . . . . 34 G . Klystrons on Mark IV . . . . . . . . . . . . . . . . . 35 High-power k lys t ron windows . . . . . . . . . . . . . . . 36 A . Window-life t e s t stand . . . . . . . . . . . . . . . . 36 B . Recirculator windows . . . . . . . . . . . . . . . . . 36 C . Other window work . . . . . . . . . . . . . . . . . . 39 Modulator s tud ie s . . . . . . . . . . . . . . . . . . . . 41 A . Project development a c t i v i t i e s . . . . . . . . . . . . 41
IX e
XI D
XI1 0
XI11 0
XIV 0
xv. XVI D
XVII 0
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . .
Vacuum sys t em.
A, Mark IV conversion
B. F e a s i b i l i t y s tud ie s
C. F'roblem s tud ie s
D. Conclusions
Support and alignment A. S i t e earth-movement s tud ies . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bo Support
C. Alignment
Control system s tudies
A. General s tud ie s
B. Design s tudies
C. Trlgger system
Research area design
A. Work completed B. Current inves t iga t ions . . . . . . . . . . . . . . .
A. Major conventional f a c i l i t i e s . . . . . . . . . . . . . . . . . . . . . . . . . . S i t e , bu i ld ings and u t i l i t i e s
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. P l a n t w a t e r . . . . . . . . . . . . . . . . . . . . . B. Cooling water
C. Blow-down water
Bo Special problems
Water system
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Research and development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Heating and v e n t i l a t i n g
Review of cont rac t work A. Early acce lera tor work a t Stanford . . . . . . . . .
Contract AT(04-3)-21, Project Agreement No. 1 . . . . A. L i s t of technica l r epor t s and papers . . . . . . . .
Abstracts of technica l r epor t s and papers . . . . . .
B" Reports and papers . . . . . . . . . . . . . . . . . . .
B.
Page
43 43 43 43 44 45 45 45 45 47 47 47 48 54 5h 54 58 58 59 60
60 60 61 61 62 63 6 3 63 66 66 68
1
LIST OF FIGURES
Page
6 1. A comparison of s t ruc ture phase var ia t ions immediately
a f t e r tuning and 17 months l a t e r . . . . . . . . . . . . . . 2. Coupler geometry f o r reducing f i e l d asymmetries . a . a . 7
3. A = def lec t ion of t h e ins ide w a l l of the disk-loaded
waveguide f o r 49.7 p s i t o t a l pressure
A comparison of measured and computed phase change vs
ex te rna l pressure for a 2 ~ ~ / 3 lo - f t uniform acce lera tor
s t ruc tu re . . . . . . . . . . . . . . . . . . . . . . . . .
10 . . . . . . . . . . . 4.
11
?ae Space-harmonic amplitude and t o t a l r / Q as a funct ion of
normalized group ve loc i ty . (For various d i sk thicknesses : 0.230, 0.120, and -060) . . . . . . . . . . . . . . . . . . 18
5b. Corrected r/Q f o r space harmonic as a funct ion of
normalized group ve loc i ty . (For various d i s k thicknesses :
0.230, 0.120, and .060 i n ) . . . . . . . . . . . . . . . . . 18 6. Phase s h i f t e r B: phase s h i f t ( 9 ) vs ambient temperature
at various cur ren ts (ima) . . . . . . . . . . . . . . . . . 7 . Phase s h i f t e r B:
at temperatures 82 F, 102'F, and 118'F . . . . . . . . . . . i n se r t ion loss i n db vs cur ren t (i ma ) 0
8. Half-wave d i sk No. 6 . . . . . . . . . . . . . . . . . . . . 9. Fa i lu re of b e r y l l i a window . . . . . . . . . . . . . . . . . 10. Bery l l i a window assembly . . . . . . . . . . . . . . . . . . 11. Trigger pulse d i s t r i b u t i o n . e a e . e . . . e . . a
12. Detail of s e l ec to r u n i t . . . . . . . . . . . . . . . . . .
29
30
38 38 40
51 52
- i v -
I. INTRODUCTION
This i s the F ina l Report on Contract AT(04-3)-21, Project Agreement
No. 1. This contract began on June 30, 1953, and ended on November 30, 1961. Sta tus Reports, and i n a number of Technical Reports and journal publi-
ca t ions . Since July 1, 1960, the S ta tus Reports f o r t h i s contract have
been combined with those f o r Contract AT(04-3) -363, because the work of t h e two cont rac ts w a s c lose ly re la ted .
The work of t h e contract has been reported i n the quar te r ly
I n b r i e f , t h e objec t ives of contract AT(04-3)-21, P.A, 1, have been
t o study the proper t ies and anomalies of the present Mark I11 and Mark
IV l i n e a r e l ec t ron acce lera tors a t Stanford University, and improvement
o f the var ious components of these machines. In addition, the contract
c a l l e d f o r s tud ies of t he f e a s i b i l i t y of extending t h e l i n e a r e lec t ron
type of acce lera tor t o multi-Bev energies.
scope of work of t h e contract was broadened t o include addi t iona l s tud ies
and research s p e c i f i c a l l y re levant t o t he then proposed Stanford two-
mile acce lera tor p ro jec t , which has since been authorized by the Congress
(September 1961), and i s now supported by Contract AT(04-3)-363.
expected t h a t a new contract , AT(04-3)-400, which w i l l cover construc-
t i o n of t h e two-mile machine, w i l l begin ea r ly i n 1962.
On August 31, 1960 the
It i s
This F ina l Report i s divided i n t o three pa r t s , as follows.
1, Sections I1 through XV cons t i t u t e the usual quar te r ly repor t s
o f t h e s t a t u s of t he individual pro jec ts .
2. Section XVI i s a b r i e f h i s t o r i c a l summary of the work of t he
cont rac t a
3. Section XVII contains a l i s t of t h e Technical Reports and journal
publ ica t ions t h a t describe work sponsored by the contract
from these r epor t s a r e a l so given as a source f o r fu ture reference,
The Abstracts
The responsible inves t iga tors f o r t h i s contract have been E" L. Ginzton and R. B. Neal.
- 2 -
r
11. MAFX IV PROGRAM
11.
The Mark IV accelerator conversion program was continued during the quarter and at year end is considered to be essentially complete.
following chronology presents the highlights of the period.
The
1. The electron gun was installed October 20th, and the cathode
was activated. A test showed a microperveance of one. 2. Modulator tests were conducted during early November, and
peak voltages in excess of 200 kv were applied to the klystrons.
Further tests and modifications of the drive system were made.
3. On November loth, rf was put into the accelerator sections for
the first time.
system.
ducted later in the month.
on these occasions. Radiation surveys indicated safe work conditions
fn the upstairs equipment room with only partial trench shielding in place.
according to pian.
Considerable outgassing was observed in the vacuum
Similar runs at gradually increased power levels were con-
Access to the trench was not permitted
The final shielding blocks were installed in early December
4. Gun-pulsing tests were conducted on November 20th and 2lst
with satisfactory results.
5 . The first beam was achieved on the machine at 1:OO p.m.,
December 8th, after several hours of start-up preparations. The
operation was reasonably smooth, although considerable trouble was
experienced with the collimators sticking both in and out of the beam
path.
6. A second run was conducted on December 14th primarily for
confirmatory purposes.
tion was estimated at 50 MeV, with an average beam current of .65 pa, as indicated by the in-line Faraday cup. (Installation of the beam
deflection system is under way and will be tested at a later date.)
Radiation readings taken at various locations adjacent to the trench
shielding were at o r below 1 mr/hr.
The maximum beam energy during stable opera-
The gradual transition to an operational status during the quarter required training and reorientation o f personnel in the Mark IV organization. This was accomplished by means of information sessions,
11.
p a r t i c i p a t i o n i n shakedown tes ts and d i r e c t experience during beam
operation.
accommodate t h e experimental-test program commencing i n January of
It is an t ic ipa ted t h a t crew and machine w i l l be ready t o
1962.
- 4 -
111, ACCELERATOR STRUCTURE AND HIGH-POWFR WAVEGCTDE COMPONENT STUDIES
A. RADJOFFEQUENCY STUDDS OF THE ACCELERATOR STRUCTURE 1. Structure Measurements and Tuning
a, S t a b i l i t y of tuning
An indica t ion of t h e s t a b i l i t y of tuning was obtained by measure-
ments on a 2.sr/3 electroforqed sec t ion tuned i n June 1960. shows the phase va r i a t ions about t h e i n i t i a l reference pos i t i on of one
arm of a Smith-plot presentat ion.
good, and there does not appear t o be any va r i a t ion between t h e measure- ments t h a t would ind ica te e i t h e r a uniform o r random detuning of the
cavit . ies.
va r i a t ion in ambient condi t ions during the measurements.
differences noticeable as the short ing plunger i s withdrawn f u r t h e r
down t h e sec t ion a re t o be expected because of t he increasing e f f e c t
of var ia t ions i n ambient conditions and inaccuracy i n the determination
of n u l l pos i t ionso
l imi ted
on Mark IV and being tuned by indenting the w a l l w i t h a 1/4-in. rounded
plunger, t h e tuning i s s t ab le f o r periods t o 1-1/2 years .
Figure 1
The correspondence i s seen t o be
The d i f fe rences that appear are probably the r e s u l t of
The larger
While the s ignif icance of a s ingle t e s t must be
it appears that , f o r electroformed sec t ions now being used
Further t e s t s of tuning s t a b i l i t y under var ious processing and
storage conditions w i l l be undertaken.
bo Symmetric f i e l d couplers
Parts a re being made t o determine dimensions f o r a matched
coupler w i t h minimized f i e l d asymmetry along radial. l i n e s about t he
ax i s , To obtain t h e des i red resul t ,one would idea l ly attempt to simulate t he boundary conditions of t he coupler i n the back w a l l of
t he cavi tyo This would result i n an unnecessarily complex geometry.
A suggestion by G o A. h e w and Oe Altenmueller, which w a s promising
i n terns of both ease of fabr ica t ion and e l e c t r i c a l c h a r a c t e r i s t i c s ,
i s being invest igated,
which is produced by taking a cut a t t h e o r i g i n a l diameter and o f f s e t
a distance xg opposite t he eoupling iris.
Figure 2 shows the change i n coupler geometry,
c. Observations of temperature and humidity e f f e c t s on measurement s
The previous repor t mentioned t h a t the temperature i n t h e RF T e s t
<
I I I 1 I I \ D c o O C U f u 3
d r i r i r i
.. .
111.
x = the offset from the accelerator axis of the second circular boring of the coupler
FJX. 2--Coupler geometry for reducing field asymmetries.
- 7 -
I .
Room w a s being cont ro l led t o within 1+OF.
t h a t can be achieved i n a room of t h i s type and usage.
change is a larger var ia t ion than desired f o r s t ruc tu re measurements,
and add i t iona l s t ruc tu re temperature cont ro l was considered.
found, however, that t h e 10- f t sect ions e f f ec t ive ly in tegra te tem-
perature f luc tua t ions , and sec t ion temperatures can be kept acceptably
constant without t he use of temperature-controlled jackets o r s i m i l a r
devices e
T h i s i s probably the best
This temperature
It was
Humidity var ia t ions , however, continue t o pose problems. E r ra t i c
measurements have been observed as a r e s u l t of humidity changes that
occurred more than e ight hours previously. This slow propagation of
humidity e f f e c t s can be avoided by c i r cu la t ing f i l t e r e d room air
through t h e sec t ion ,
from gradual changes i n room humidity during measurements.
some of these d i f f i c u l t i e s , we are considering t h e p o s s i b i l i t y of
making measurements and tuning w i t h a moderate ( l o m 3 mm Hg) vacuum
within the sec t ion .
D r i f t s i n da ta have a l so been observed t o r e s u l t
To avoed
2, Resonant-Structure T e s t s
The first tes t i n t h i s s e r i e s w a s an attempt t o compare outgassing
caused by high f i e l d s and by d iss ipa ted power,
system w a s found t o be
independent of t h e rf l eve l s .
the establishment of a near ly- ideal reference condition. We are con-
s ider ing exposing c a v i t i e s t o various standard "d i r ty" conditions f o r
fu tu re tests
3. Calculat ions have been made t o determine p r inc ipa l e l a s t i c de-
The pressure i n the
2 X lo-' mm Hg (pumped by a Vacion 'jL pump)
This i n t e r e s t i n g r e s u l t demonstrates
Dependence of Phase on External Pressure
formations of the w a l l and t h e disks of the disk-loaded waveguide,
The ca l cu la t ions of t he r a d i a l def lec t ions were made by coupling the
general theory of cy l ind r i ca l s h e l l s w i t h the theory of thick-walled
cyl inders . A l l t h e ca lcu la t ions were ca r r i ed out assuming a difference
between ex te rna l and i n t e r n a l pressure t o be
The de f l ec t ions given are changes i n r a d i a l dimensions; they are one- half of the changes i n diameters.
35 p s i + 14.7 p s i = 49.7 ps i .
Loads and def lec t ions a re proport ional throughout t he e l a s t i c
range, The following p l o t s w i l l , therefore , give def lec t ions f o r any
- 8 -
1
I11 D
pressure i f the proper pressure r a t i o i s applied t o the p lo t ted values.
Deflection of t he waveguide w a l l f o r one cavi ty of t he constant-
a t tenuat ion sect ion i s p lo t ted on Fige 3. mately 16.8 x 49.7 p s i t o t a l pressure.
t h i ck d isk w i l l have a r a d i a l def lec t ion of 10.0 x i n ,
This plot gives approxi-
i n . max r a d i a l def lect ion a t the mid-span f o r
A t t h i s pressure the hole i n the .23O-in.
Calculation of t he r a d i a l def lec t ion of the w a l l has a l so been
ca r r i ed out f o r a th inner d isk .121-in. thick, assuming t h i s d i sk does
not buckle. The center distance, 1.378 in . between disks, i s t h e same
as i n the e a r l i e r case. The maximum def lec t ion a t the middle of t he
span between d isks i s
def lec t ion of t he hole i s
20.72 x lom6 in", and the corresponding r a d i a l
13.4 x LOw6 i n .
For the constant-gradient sect ion the o ,d , i s kept comtant a t
4,000 i n , , while the i . d . va r i e s from 3.288L i n , f o r the f i r s t cavi ty
to 3,2190 i n , f o r the 87th cavi ty , cavi ty has been calculated a t 17.53 x i n . and f o r the 87th
cavi ty a t l b e a r l y would, i n most cases, be su f f i c i en t ly accurate,
The max def lec t ion of t he f i r s t
16"21 x lom6 in . The assumption t h a t the def lec t ion va r i e s
Measurements were made of the change i n phase r e su l t i ng from
the appl icat ion of ex terna l pressure t o an electroformed 2fl/3 uniform
sect iono
o r very nearly a full 10-f t sect ion length,
r e s u l t of' computations of def lect ion, which indicated t h a t an appre-
c iab le e f f e c t on the propagation constant would r e s u l t from the
appl i2at ion of pressures required fo r some Por)Kng methods that are
being eons ide r e d
Changes i n t o t a l phase s h i f t were measured over 80 cavi t ies ,
The t e s t s were made as a
The phase s h i f t expected from the predicted def lec t ion of t he
inner w a l l and d isk hole i s shown i n Fig. 4 along wi-th the phase
measurements,
2n/3 uniform sect ions by pressurizing the water jacket ,
were electroformed.
The l a t t e r were taken on one of the o r i g i n a l Mark I V
These sect ions
It i s c lear t h a t applying moderate pressure -C;o the acce lera tor w a l l
can cause s ign i f i can t mounts of phase shif i .
consider t he phase change possible as a r e s u l t of barometric-pressure
It i s in t e re s t ing t o
- 9 -
1
t .375 in.
1.378 in. - c
Note: radial deflection of hole in disk: nH = 10. o x in.
.10 in. .5O in.
10 x
I
20 x 10-6 -
A
FIG. 3 - - A = deflection of the inside wall of the disk-loaded waveguide for 49.7 psi total pressure.
... - - 10 -
. .- ,
/
i B \ R I - - 40 50 20 30
0 0 10
Pressure ( p s i )
FIG. 4--A comparison of lneasured and computed phase change vs ex terna l pressure for a 2g/3 10-ft uniform accelerat,or s t ruc ture .
- 11 -
var i a t ions .
a change i n absolute pressure of 1/2 p s i and a phase e r r o r of .07°/section.
A change of 1 i n . i n barometric pressure w i l l result i n
4, High-Power RF-Test Area
Detailed p lans were made f o r a high-power t e s t area, -____I__
Early f u l l -
power t e s t s of the acce lera tor s t ruc ture and waveguide components will
be c a r r i e d out here,
t h a t f o r the resonant-structure t e s t s .
begun.
The f irst equipment t o be located here w i l l be
Preparation f o r t h i s move has
5. The need f o r a frequency standard was considered, along w i t h
A s a r e s u l t , we are obtaining a high-
Establishment of a Frequency Standard
systems f o r s a t i s f y i n g it.
stability o s c i l l a t o r and very low frequency ( v l f ) rece iver and com-
par i son equipment. The advantages of t he v l f system f o r frequency
determination a re high accuracy i n a given t i m e ( 3 p a r t s i n LO9 i n one
hour) s implici ty , and r e l a t i v e l y low cos t
B. ELECTROFORMING
The s m a l l f a c i l i t y f o r e l ec t rop la t ing 10 - f t lengths has been
f in i shed f o r some time. A Universal p l a t i n g rack t h a t w i l l hold the
1 0 - f t s ec t ion halfway immersed i n the p l a t ing so lu t ion has a l so been
flni,shed,
t h e I O - f t sec t ions at, speeds from 0-to-100 rpm, and a variable-speed
agate burnishing mechanism .I
The rack includes a variable-speed gear motor t h a t can turn
A 10 - f t dummy w l ~ l l b e t r i e d out i n t h e l a s t p a r t of 196s and
t h e f i r s t sec t ion i n t h e beginning of 1962.
C. BRAZING
The 1 0 - f t v e r t i c a l brazing furnace has been completed and has
been t e s t e d w i t h dummy pieces of disk-loaded waveguide cons is t ing of
s t r a i g h t copper tubing, It has performed s a t i s f a c t o r i l y , and we ex-
pect t o braze the f i rs t I O - f t lengths ea r ly i n t,he next quar te r ,
- 12 -
1
Do WATER JACKET
The reduced-pressure-boiling t e s t setup w a s completed, and preliminary
tests performed,
i s sa t i s f ac to ry and t h a t t he bas ic system i s capable of operating over
the desired range of conditions.
i n maintaining the reduced pressure and a uniform heat Input.
pressure-control system has been obtained and in s t a l l ed .
method has been modified i n order t o obtain a more uniform heat-input
distribuxion, and the system i s ready f o r t e s t ing .
The tes t runs have indicated t h a t the i n s t m e n t a t i o n
However, some d i f f f c u l t y was experienced
A new
The heat-input
The small-scale, cross-flow-test mockup was set up and t e s t s per-
formed, The tests have shown conclusively tha t unless an extremely
la rge amount of water is used, t h e cross-flow method of cooling the
acce lera tor cannot meet the 5 114 F temperature-control requirement. 0
A water jacket has been designed f o r use w i t h constant-attenuation
accelerator sec t ions , The same bas ic jacket design w i t h minor modifi-
cations can be used f o r the constant-gradient accelerator . In t h i s
d2sign a constant flow of water t r a v e l s a s p i r a l path along t h e ac-
ce le ra tor tube f o r t he constant-attenuation case. For constant-gradient
operation the same flow path i s used, but t he water-flow r a t e i s in-
creased as the flow progresses along the acce lera tor tube.
The drawings and spec i f ica t ions f o r t h i s jacket ( f o r both appl i -
ca t ions) have been completed. The jacket i s intended t o be used as a
test vehicle f o r developmental t e s t s of other acce lera tor components.
It, probably w i l l not be used fo r the two-mile accelerator , because it
wouldbe d i f f i c u l t t o f ab r i ca t e and t o i n s t a l l ,
Another promising water-jacket concept is cur ren t ly being inves t i -
gatedo
d i r e c t l y onto the surface of the accelerator*
d i r ec t ion through a l l tubes for constant-attenuation sect ions, and i n
opposfte d i rec t ions in adjacent tubes f o r constant-gradient sec t ions .
This method appears t o have the advantage of s impl ic i ty of f ab r i ca t ion
and i n s t a l l a t i o n over a l l other schemes considered. T e s t samples are
being made t o determine the p o s s i b i l i t y of brazing the tubes in a s ingle operation i n the v e r t i c a l brazfng fmnace.
t h i s concept has been designed and is cur ren t ly being f&ibrieated.
In t h i s cooling method, 18 one-half-inch o.d, tubes are brazed
Water flows i n one
A t es t system t o evaluate
ITI.
E 0 HIGH- FO'R WAVEGUIDE COMPONENTS
P r i m a r y emphasis i s being placed on the development of a waveguide-
vacuum valve.
and with low-level microwave measurements. Additionally, a fu l l - sca l e
mockup of the separation between the k lys t ron ga l le ry and the acce lera tor
enclosure is under construction,
t h e performance of the waveguide connection between the klystrons and
the acce lera tor , Further, the setup w i l l be used for the development
of i n s t a l l a t i o n procedures.
Two spec i f ic designs are being evaluated ana ly t i ca l ly
This setup w i l l allow the t e s t i n g of
The i .d . cross sect ion f o r the waveguide has been set at 2,840 in . x 1.340 in .
ye t t o be determined.
The w a l l thickness and method of cooling have
- 14 -
1
IV. I N J E C T I O N SYSTEN
A. MARK I V CONVERSION PROGMM
The Mark IV gun and gun modulator operated s a t i s f a c t o r i l y during
t h e i n i t i a l beam t e s t i n g of t he Mark I V accelerator . The gun current
w a s measured t o be 15 pa average with a f i rs t anode pulse of approxi-
mately 4 kv, and a cathode pulse o f 75 kv.
B. COMPARISON OF TWO B A S I C T Y P E S OF INJECTORS
Two types of i n j ec to r s have been proposed f o r Project M. 1. The in - l ine in j ec t ion system i n which a hollow cathode gun'
i s loca ted on t h e a x i s of t h e accelerator .
2. The in f l ec t ion (of f -ax is ) in jec t ion system.
A study of t h e f e a s i b i l i t y , comparative advantages and cos t s of these
two systems has been undertaken and w i l l continue during t h e next
quarter . The cos t study ind ica tes t h a t t he i n s t a l l e d cos t per i n j ec to r
w i l l be subs t an t i a l ly less f o r an on-axis i n j ec to r than f o r an in f l ec t ion -
type i n j e c t o r .
C. GUN S P E C I F I C A T I O N S
Preliminary spec i f ica t ions f o r a conventional type gun h&ve been
prepared. A survey of tube and gun manufacturers has been i n i t i a t e d t o
see i f a stock gun e x i s t s t h a t meets these spec i f ica t ions .
D. TWO-ELEME-W' BUNCHER
Tentat ive choice of a buncher has been made pending: (1) a de ta i led
numerical i n t eg ra t ion t o evaluate the e f f ec t of space harmonic and
r a d i a l forces , and ( 2 ) a n experimental t es t .
two elements and should bunch 8% of t h e in jec ted e lec t rons i n t o a phase
i n t e r v a l of 35' t h a t w i l l form a 3 O bunch i n the f i r s t 1 0 - f t sect ion of
acce lera tor . The f i r s t element of t he buncher i s a uniform see t ion of
disk-loaded waveguide with phase ve loc i ty equal t o the ve loc i ty of t h e
in j ec t ed e lec t rons v = .5c. This sect ion i s about 30-in. long and
requi res about 2-kw peak dr ive power. The second element i s a s imi la r
sec t ion wi th phase ve loc i ty v = .7c. This sect ion i s 6-in. long and
The buncher cons is t s of
P
P
'If simultaneous beams are not needed, a conventional gun can be mechanically in se r t ed by remote control.
- 15 -
requi res 500-kw peak dr ive power" The electrons leave the second element 0 of the buncher as a 33
t i o n o f t h e e lec t rons i n the second element of t he buncher decreases t h e
power required i n t h e f irst 10- f t accelerator sec t ion by a f a c t o r of" two.
The first 10-f t acce le ra tor sec t ion w i l l be designed t o require 10-to-12
Mw peak power f o r optimum capture and bunching i n order t o achieve exce l len t
klystron r e l i a b i l i t y e
bunch with average veloci ty o f 0 . 7 ~ ~ The accelera-
- 16 -
I 7
. .
V.
V. MICROWAVE CIRCUITS
A. GENERAL RF STUDIES 1, Constant-Gradient Accelerator Structure
a , Coupler design
A brazed 2 - f t sec t ion corresponding t o the first nine c a v i t i e s of
the constant-gradient s t ruc tu re became avai lable during t h i s period.
Using t h i s sect ion, t he input coupler was matched. The cor rec t dimen-
s ions a r e :
2b = 3,228 in .
Iris aperture = 1.160 i n .
b . Group ve loc i ty and qua l i ty f a c t o r Q
Using the nine-cavity sect ion mentioned above,a measurement of t h e
average group ve loc i ty was made, y ie ld ing a value of vg/c = .0205 as predic ted by design.
y ie ldfng a Q of l l J O O , This value appears somewhat low and may be
ascr ibed t o t h e f a c t t ha t t he brazing of a t l e a s t one cavi ty i s de f i c i en t .
These measurements w i l l be v e r i f i e d during the next quar te r by using a
b e t t e r sec t ion .
The a t tenuat ion constant turned out t o be .I26 nep/m,
c Measurements of r / Q and space-harmonic amplitude
The t e s t s concerning the measurement of t he field-space-harmonic
amplitude of acce lera tor sect ions with d i sk thicknesses of .23O in . ,
o120 i n . and .060 i n , as a funct ion of group ve loc i ty have been completed.
All results appear i n Fig. 5aa This f igu re gives experimental po in ts i n
the range of v / c between .OO5 and .022,
Y /c = 0 The th ree lower
poin ts correspond t o t h e thicknesses of .23O in . , .120 i n . and .060 i n .
The four th point corresponds t o an i n f i n i t e l y t h i n d isk . Also p lo t t ed
on t h i s figure are experimental curves of t he t o t a l value ( f o r a l l space
harmonics) of r /Q . T h i s t o t a l value i s labeled as rT/Q. Figure 5b gives t h e curves f o r the corrected values of
first space harmonic alone. This value is labe led as r /&. From these
r e s u l t s it i s seen tha t the re i s a d e f i n i t e advantage i n going t o a disk
th inner than 0.230 in . , i f mechanical and thermal proper t ies allow.
The four poin ts shown f o r g
were obtained from t h e o r e t i c a l ca lcu la t ions . g
r / Q corresponding t o t h e
0
.86
.84
.ao
.78
.76
.74
.72
.7c
.68
. 6 E
.64
J 2nI3 MODE -
5
0
15
10
15
10
15 FIG. 5a- -SPACE-HARMONIC AMPLITUDE AND T O T A L r/Q AS A
FUNCTION OF NORMALIZED GROUP VELOCITY. (For various disk thicknesses: 0.230, 0.120, and ,060)
1 1 1 50 0.015 0.020 0.025
35 1 ,230" (For Fundamental Space Harmonic)
"h- I
FIG. 5b--CORRECTED r/Q FOR SPACE HARMONIC AS A FUNCTION OF NORMALIZED GROUP VELOCITY. (For various disk thicknesses : 0.230, 0.120, and ,060)
- 18 -
d. Constant-gradient f i e l d s tud ies
The results given i n Fig. 3 of t h e previous S ta tus Report2 were found
t o be i n e r ro r .
sults.
caused by drawing a d i e l e c t r i c bead along i t s ax i s can be calculated as
follows :
A mistake w a s made i n normalizing and p l o t t i n g the re- The phase-shift v a r i a t i o n across a matched acce lera tor sec t ion
where ,E i s the d i e l e c t r i c constant of t h e bead, AV i s i t s volume,
P i s the power flow, W
cavi ty , and
from t h i s experiment i s not proport ional t o r /Q(- E2/coW) bu t t o E2/P.
By r e p l o t t i n g the curve and cor rec t ing f o r t he v a r i a t i o n of t h e group
ve loc i ty along the s t ruc tu re , it i s found tha t
i s the energy stored, d i s the length of one
i s the length of a sect ion. Thus, t h e curve obtained
From the design
= l .g/meter
The agreement i s f a i r .
as a complete and matched constant-gradient sec t ion becomes avai lable .
T h i s ?hole experiment w i l l be redone as soon
2. Coupler-Asymmetry Measurements
Previous t e s t s t o measure the axial f ie ld asymmetry i n a coupler
caused by the opening of the coupling i r i s were based on the measurement
!
,Status Report, M Report No. 280, Project M, Stanford University, Stanford, C d i f o r n i a , October 1961.
- 19 -
v.
of t he phase s h i r t across the whole sect ion produced by a d i e l e c t r i c
bead drawn perpendicularly t o t h e coupler axis. lengthy and d i f f i c u l t t o perform.
appears much simpler.
coupler by in se r t ing an e l e c t r i c probe in to the first d isk hole.
su f f i c i en t t o introduce t h e probe v e r y d i g h t l y i n order t o pfck up a
s ignal .
f o r t h e previous method, t h e asymmetry or symmetry ( r e s u l t i n g from a
corrected couplelo) i s immediately apparent. O f course, t h i s method does not permit sampling of the f ie ld at a radius grea te r than t h e d i sk hole,
bu t these measurements are of no p r a c t i c a l i n t e r e s t s ince t h e e l ec t ron
beam never sees those f i e l d s anyway.
These tests were r a the r
A new method has been derived t h a t
The pPincipEe i s t o sample the f ie ld ins ide the
It i s
Although t h e i n t e r p r e t a t i o n of the curves i s not as obvious as
3. Using the r e s u l t s of Report No. 5105, P. N. Robson, Metropolitan-
Group-Velocity Measurements i n Cavity Tests
Vickers Co., Ltd., quoted i n t h e previous Status and f u r t h e r
approximations such as S t i r l i n g ' s in te rpola t ion formula, it was found tha t more accurate values of the group ve loc i ty can be obtained than
from t h e simple graphical method. By using s i x c a v i t i e s and t h e re-
s u l t i n g seven resonant frequencies on the cu-p p lo t , the S t i r l i n g
in t e rpo la t ion formula gives group v e l o c i t i e s about 3% higher than ob-
ta ined before.
4. Prebwncher Studies
The prebuncher mentioned i n the previous S ta tus Report4 has under-
gone f i n a l assembly and i s now being t e s t e d before i n s t a l l a t i o n on the
Mark IV. 5 . Propert ies of S-Band Waveguides
The choice of t h e c ross sec t ion f o r t he 3 O - f t waveguide jo in ing
the klystron t o the acce lera tor sec t ions i n the , Project M acce le ra tor
must be based on a va r i e ty of c r i t e r i a such as rf, mechanical, v&cum
proper t ies and f i n a l cos t .
p roper t ies were ca lcu la ted f o r two types of rectangular S-band waveguide.
The r e s u l t s a r e shown i n Table I.
I n order t o make t h i s choice, per t inent rf
It seems t h a t t he advantages gained
3M-280, op. c i t . , p. 19.
4Toid,, __9 p. 17.
- 20 -
TABLE I
RF PROPERTIES OF STANDARD AND ODD-SIZE S-BAND WAVEGUIDES
Standard S-Band Waveguide Odd-Size S-Band Waveguide
a = 2.840 in . a = 3.900 i n .
b = 1.340 in. b = 1.950 in . = 2080 Mc/sec
= 15.32 ern a t 2856 Mcfsec
f c = 1514 Me fsec
X g = 12.40 cm a t 2856 Mc/sec f C
X g Rs = 1.395 x ohms Rs = 1.395 X ohms
Attenuat ion of TE,, Mode a t 2856 Mcfsec
a = 2.38 x nep/m a = 1.124 x nep/m
a = 2.067 x db/m a = 6.30 x dbfft a = 2.976 x db/ft
a = 9.763 x lo-” db/m
At tenuat ion of Higher Modes
TEol a = 610 dbfm
a = 703 db/m
a = 703 dbfm 1
a = 312 d:b/m
a = 338 db/m TEol
a = 338 d b f m TE1 1
0 Phase-Shift Change i n Degrees-per- C Change f o r 5O-ft Length
6q = 1 . 2 3 O f 0 C Ecp = 0.92’ f0C
Average Heat Dissipation i n 5O-ft Length
c a l = 6 mJm = 0.97 x 10;’ -
I c a l
P. in. = 6 M W , ~ = 2.78 x loe3 - ern 2 ’in,
- 21 -
v.
from going t o a cross sect ion wider than t h a t of the standard S-band
guide a r e not suf f ic ien t t o warrant i t s extra cost . A more de ta i led
discussion of t h i s top ic w i l l be given i n a la ter report .
6. A ca lcu la t ion of the heat diss ipated i n a standard S-band wave-
The r e s u l t s are
Heat Dissipation i n S-Band Waveguide
guide w a s made t o design an optimum cooling system.
shown i n Table 11.
7. I n Stage I of the accelerator construction, each high-power klystron
Reflections i n &-Way Power S p l i t
w i l l feed four accelerator sect ions.
four ways i n the pa t te rn of a Christmas t r e e ( w i t h the klystron on top) by means of t.hree o r two T ' s (depending on whether the klystron has a
s ing le or double output) .
the power and phase var ia t ions caused i n any three sections by the re-
f l e c t i o n of power i n the four th sect ion (due t o a sudden breakdown o r
gas b u r s t i n the sec t ion) . This calculat ion cannot be completed a t
t h i s t i m e because t h e standing-wave r a t i o looking back i n t o the klystron
i s not known. However, it i s c e r t a i n t h a t the power s p l i t s must be
achieved by means of magic T's capable of i s o l a t i n g the mismatch caused
by one sect ion breaking down. An addi t ional advantage can a l so be
gained from using magic T's. Since i n the Christmas t r e e arrangement
a l l four waveguide lengths from klystron t o accelerator m u s t be equal,
it w i l l be possible t o insure t h i s equal i ty upon i n s t a l l a t i o n by de-
tuning t h e f irst cavi ty of the accelerator sect ions and adjust ing the
waveguide runs u n t i l no power appears i n the four th arm of each magic T.
Al ternat ively, instead of detuning the f irst cavity, another method
would consis t of sending a frequency f o r which the accelerator input
i r i s a c t s as a per fec t short .
The power s p l i t w i l l be achieved
A calculat ion has been car r ied out t o predict
8, Pumpout Work
Work has started on a pumpout i n the form of an H-plane ?'-junction
w i t h a band-elimination f i l t e r consis t ing of two posts placed so as
t o present; zero impedance t o the pumpout arm. Two models have been
constructed and high-power tests w i l l be made i n the next quarter .
9. Waveguide-Vacuum Valve
Work has a l s o started on a waveguide-vacuum valve. The present
model i s being t e s t e d f o r rf propert ies t o ascer ta in whether it can be
matched without using irises. Results appear encouraging.
- 22 - _. . 1
v.
TABLE I1 POWER D I S S I P A T I O N I N RECTANGULAR S-BAND WAVEGUIDE FOR T H E TE,, MODE
a = 2.840 in. = 7.22 em b = 1.340 in. = 3.41 em ho = 10.5 cm
P and Px are the average powers dissipated in the top or bottom Y
and side walls respectively.
and h is the free-space wavelength.
For standard S-band guide, and ho = 10.5 em, these expressions yield
P Y = K
A n approximate plot i s shown below.
The total powers Pv and Pv are obtained by integration. - h .J
- - - aRs Eo2
- 'y total q2
- - - - 4 v2 'x total
2a' - = 2 for standard S-band guide at Xo2b
The ratio is
The power dissipation appears to be practically constant around the guide.
It can easily be shown that for any Tno mode, the above ratio is
lo = 10.5 cm.
2a3 pX - =
2 2 P n lob Y
- 23 - T
B. DRIVE SYSTEM
1. Design Studies
More work was done during the pa.st period to examine alternative
solutions to the drive system for the accelerator. The design using a
coax drive line is still preferred at this time. However, a proposal
has been made to transmit the master signal at a lower frequency (1.19 Mc/sec) at which the loss is small enough to allow elimination of all series
boosters. This proposal, however, has the disadvantage that frequency
multipliers must be incorporated ahead of each sub-booster. Although
much progress has been made in designing frequency multipliers with
varactor diodes, it is not certain at this point whether the required
phase stability can be obtained with these devices. Work on this design
will continue throughout the next two quarters.
2. Mark IV Drive Svstem The rf system for the Mark IV was completed during this quarter and
has been in operation for about one month. A peak power of approximately 500 w at a pulse length of about 7 psec is available at each klystron. An instruction manual of -the system for the operating and maintenance
pel-sonnel is being prepared.
3. Radiofrequency Driver
The rf driver built by Granger Associates of Palo Alto was accepted
during the past period.
of the driver appeared satisfactory, as seen from Table 111.
After a number of corrective measures, operation
4. Freauencv and Phase Measurements
The frequency-stability measurement of the Granger driver was done
by observing the beat between its cw output and another stable source
(a Hewlett-Packard transfer oscillator) e
by less than 2 kc during a few milliseconds. This number includes the ,
stability o f both sources.
The "period" of the beat varies
In order to perform the phase-stability measurements, work is being
done on two different methods. The first was suggested at Varian Asso-
ciates. It is based on comparing the input and output pulses from the last amplifier stage o f the driver with a local oscillator (oPf by about
30 Mc/sec), mixing the signals, picking out the 30 Mc beat, amplifying
and clipping the signals and finally feeding them into a phase detector
operating at i.f. This scheme has worked very well at cw but must now
be adapted to pulsed operation.
- 24 -
v.
TABIE 111
GRANGEX DRIVER REQUIRED SPECTFICATIONS AND MEASKWD CHARACTERISTICS
C hal-ac t e r i st i c s
rain rf power output
bwer-amplitude s t a b i l i t y (pulse t o pu lse)
lenter frequency
'requency t2uning
Ihort -term frequency s t a b i l i t y o f cw output
Late of change of phase s h i f t
)ong-term frequency s t a b i l i t y
;purious frequencies above 1000 Mc/sec i n the output of t h e system, a t l e a s t
3 d s e spec i f i ca t ions
Length
Rise t i m e
T ime Qittel- r e f e r r ed t o main sync. t r i g g e r
k l se-he ight deviat ion from f l a t n e s s
~
Required
5000 w
+ 1% 2837.3 Mc/sec
< 2'/3 psec
i 5 kc(for 1 h r )
50 db down
3 wsec
0 0 2 psec max
0.02 psec '
i 1% over 3 psec
5400 w
<< 1%
2837.53 Mc/sec
- 2.3 Mc/sec i- 1.6 Mc/sec
< 2kc during a time of t he order of m i l l i - seconds (see tex t )
-~
(see t e x t )
0.38 kc during 40 rnin
Nothing v i s i b l e betweer 2600 and 2930 Mc/sec, 30 db down
7 psec at 60 pps 6 , 1 psec a t 360 pps
N Oo2 psec
Not measurable with suf fi.c i e n t accuracy because of main t r i g g e r j i t t e r
i 0.2576 over 6 psec
V.
The o ther method has been proposed by the Rantec Corporation of
Galabasas, Gaiifornia. It uses a bridge with four magic 9'"s. A cw reference s igna l i s fed i n t o one of t he arms of t he bridge and the pulsed
s igna l comes i n t o the o ther a r m . The bridge i s arranged i n such a way
t h a t i t s outputs a re proportional t o the s ine and cosine of t he phase
modulation i n the pulsed s ignal .
played on a scope o r f ed i n t o a rati.0 meter giving the tangent of t he
phase modulation.
s t a r t e d and w i l l be continued during the next period.
Hence, these outputs can e i t h e r be d i s -
Tests on the Rantec phase discr iminator have been
5 . Sub-Boosters
Following some d i f f i c u l t i e s with t h e i r f i laments, t he TH-2101
k lys t rons on loan from the CFTH Company of France were flown back t o
Par i s and checked, According t o the manufacturer, the beam modulation
caused by t h e fi laments disappears completely when the tubes a re driven
i n t o sa tura t ion . The tubes a re now back i n t h i s laboratory and fu r the r
t e s t s w i l l be performed,
C . PHASING SYSTEM 1, Current Variation Detection Technique of Phasing
This method of phasing Long Pinear acce lera tors was formerly ca l l ed
t h e "beam energy maximization" technique.
i n analyzed beam current t h a t i s detected and not t h e change i n beam
energy, t h i s more appropriate t i t l e has been adopted.
However, since it i s the change
A de t a i l ed ana lys i s of t h i s technique has been ca r r i ed out aPter
s impl i f ica t ion of t he problem by approximating the energy spectrum by
a t r i a n g l e ,
foy a number of d i f f e r e n t spec t ra has been considered. Numerical examples
f o r t he order of magnitude o f the change i n current and t h e required
s e n s i t i v i t y of the de tec tor have been ca lcu la ted using t h e ex i s t ing
Project M spec i f i ca t ions , A separate report i s being prepared giving
d e t a i l s of" these calculat ions.
The e f f e c t o f the energy-spectrum shape on analyzed current
20 Mark I11 Experiments
An attempt w a s made t o simulate the "current va r i a t ion detection"
technique of phasing on t h e Mark I11 acce lera tor .
phase s h i f t e r was i n s t a l l e d on the dr ive of t h e last Mark 111 klystron,
and i t s dr ive power w a s reduced t o a l e v e l y ie ld ing an output power of
A remotely-controlled
- 26 -
'V .
about 300-kw peak.
the t o t a l beam of about 1/2$ and thereby simulates t h e e f f e c t of one
klystron being phased at f u l l power on the 2-mile accelerator .
phase of t h i s under-driven klystron was modulated by hand, t he dr ive
w a s turned on and of f and the e f f ec t w a s observed on the analyzed current
of t he acce lera tor .
o ther va r i a t ions swamped out the varying contr ibut ion of t he last klystron.
It i s a l so poss ib le t ha t the e f f e c t was not seen because a t t h i s very low
power the corresponding acce lera tor sect ion w a s too cold t o operate i n
synchronism-
5 ma, it is poss ib le t h a t t h i s last sec t ion was operating a t considerable
beam loading; thePefore, i t s contr ibut ion w a s too s m a l l t o be seen.
Another attempt t o e l iminate these d i f f i c u l t i e s and tes t t h i s method of phasing w i l l soon be made,
Mark Tv with a separate cavi ty i n l i n e w i t h the beam.
T h i s power corresponds t o an e n e r a contr ibut ion t o
While t h e
Unfortunately, the beam was not s t ab le enough, and
Also, even though t h e t o t a l beam current was reduced below
A similar experiment i s being planned on t h e
3. Induction Method
Phasing of a Non-synchronous Accelerator Section by the Beam-
M Report Noo 288, carrying t h i s t i t l e , w a s published during the pas t
quart e r
4. Th is method makes use of the s igna l induced by the beam i n a separate
Phasing Method using a Separate Cavity
cavi ty i n l i n e w i t h t h e acce lera tor sec t ion and connected t o it through a
cutoff waveguide,
i n 1957. T h i s scheme was o r ig ina l ly proposed by IC. B. Mallory
5 . Redesign of Phase Detector
The phase de tec tor previously used f o r the beam-induction method
of phasing fs present ly being redesigned.
6 F e m i t e Components
The f a c i l i t y w i t h which f e r r i t e phase s h i f t e r s and a t tenuators can
be remotely control led, and t h e i r usual ly s m a l l s ize , have l e d t o t h e i r
considerat ion f o r use f n the rf system of Project M. In connection w i t h
t he prepara t ion of t he spec i f ica t ions f o r these phase shifters, i so l a to r s ,
and attenuators, a nubey of detailed microwave measurements have been
undertaken on ava i lab le components,
'
Effo r t so far has been d i rec ted
5 G e A. LOew, " a a s i n g of a Nonsynchronous Accelerator Section by the Beam-Induction Method," M Report No. 288, Project M, Stanford University, Stanford, Cal i fornia , November 1 9 6 ~ - 27 -
.. 1
towards t h e phase sh i f te r , but measurements on the a t tenuators and iso-
l a t o r s a re planned.
vironmental and operating conditions i s of considerable importance.
The s t a b i l i t y of the components under varying en-
v p i c a l results f o r one type of e lec t ronica l ly-cont ro l led ferr i te
phase s h i f t e r are shown i n Fig. 6, which gives t h e va r i a t ion i n phase
s h i f t as a funct ion of temperature f o r a given value of cont ro l current .
The change i n in se r t ion l o s s as a function of cont ro l current f o r th ree
temperatures is shown i n Fig. 7. Considerable va r i a t ions i n in se r t ion
loss as a funct ion of power l e v e l have also been observed.
de t a i l ed study of t h i s phenomenon i s planned, together w i t h an inves t i -
gat ion of t h e hys te res i s e f f e c t s i n f e r r i t e compomnts of t h i s type.
A more
Present ind ica t ions show that considerable development work is s t i l l
required on these components before they w i l l meet the proposed specf-
f k a t ions
-i = 60 -
3-00
= 30
I I I I I 1
= 20
= 10
= o
FIG. 6 - -~hase s h i f t e r B: phase s h i f t ( c p ) vs ambient temperature at various currents (i ). ma
- 29 -
3
- 30 -
VI.
V I . KLYSTRON STUDIES
During t h e l a s t quar te r t he Klystron Group has continued i t s research
on permanent-magnet-focused klystrons, l i f e t e s t i n g of exis t ing klystron s t ruc tures , and maintenance of an adequate stock of tubes f o r acce lera tor
and component s tud ies and has begun an analysis of t he number o f tubes
needed between now and beam-on time of the Project M accelerator . In
addition, t he present subcontracts a re being carefu l ly monitored and plans
a re being l a i d f o r procurement of the klystrons needed f o r the accelerator
ope rat ion.
A. TUBE COMFTJZNENT AND PERFORMANCE The complement of tubes on hand remains e s s e n t i a l l y constant; t ha t
i s , t he tubes t h a t have f a i l e d on l i f e test a re being replaced a t a
regular rate.
We a re at present bui lding two kinds of tubes, the "long" tube and
t h e "shortrr tube. The long tube i s iden t i ca l i n e l e c t r i c a l cha rac t e r i s t i c s
t o those t h a t have been b u i l t f o r the last two years .
the long tube on l i f e t e s t s .
M Report No. 280~) spec i f i ca l ly f o r use w i t h permanent magnet.
reasons t h a t a re not ye t c l ea r , t he gain and ef f ic iency of t h e short
tube a re not as high as expected.
d ica ted that t h e short-tube gain might decrease by 3 db over the long-
tube gain, but i n prac t ice the decrease i n gain i s c lose r t o 6 o r 8 db.
Similar ly , t he change i n length i n t h e d r i f t tubes was expected t o have
l i t t l e o r no e f f e c t on the eff ic iency. In prac t ice , the short tubes have
i n f a c t shown an e f f ic iency of approximately 32$,as against 38% f o r t h e
long tubes.
We a re now using
The short tube has been designed (see
For
Specif ical ly , the computations in-
A i e r ious study of t h i s decrease i n gain and ef f ic iency i s now
being undertaken, and some spec ia l tubes w i l l be b u i l t t o determine what
remedial measures have t o be taken.
We have a l so begun the production of p a r t s w i t h which t o bu i ld
tubes t h a t w i l l conform t o the general ou t l ine of t he klystron decided
upon i n February, and which appeared i n the quar te r ly s t a t u s report of
%ta tus Report, M Report No. 280, Project M, Stanford University, Stanford, Cal i fornia , October 1961.
- 31 -
Apri l 1-961.~ and the f i rs t tubes of t h i s va r i e ty should be avai lable during the next
quar te r f o r i n i t i a l t e s t s .
The program of construction of these tubes i s wel l under way,
B e RESEARCH AND DEVELOpMEllT SUBCONTRACTS
A t t he present time both subcontractors (Sperry Gyroscope and RCA)
are behind schedule.
t h e end of February. These w i l l . be permanent-magnet-focused tubes, I n
addi t ion, Sperry w i l l de l iver two electromagnet-focused tubes f o r our
evaluat ion of t h e i r b e s t e l e c t r i c a l design,
Sperry i s now planning t o de l iver th ree tubes by
The RCA subcontract did not contemplate the del ivery of any tubes
before January 1962. observe one of t h e i r tubes i n operation, bu t during the tes ts of t h a t
tube an output window f a i l e d by puncturing and cracking,
w a s removed, the tube went down t o air and w a s scheduled f o r immediate
r epa i r s . In general, t h e RCA tubes follow very c lose ly the e l e c t r i c a l
design of t he Stanford tubes.
performance, although c e r t a i n measurement d i f f i c u l t i e s make an accurate
evaluat ion of the t e s t r e s u l t s d i f f i c u l t . The mechanical design of t he
RCA tube i s qui te novel, but has ye t t o be proven out .
During our l as t v i s i t s a t RCA we were able t o
When the load
The f i r s t t e s t s ind ica te very similar
C. NEW FACILITIES
The l ack of gases and chemical cleaning f a c i l i t i e s a r e s t i l l
hampering the operations of t he tube shop.
t h e k lys t ron developmedt program i s not y e t i n operation.
t i o n a l t e s t s on al l -metal high-power loads have not been completed
because of various mechanical d i f f i c u l t i e s t h a t
The t h i r d modulator f o r
Addi-
7Status Report, M Report No. 260, Project M. Stanford University, Stanford, Cal i fornia , Apri l 1961.
- 32 -
VI.
were encountered i n t h e fabr ica t ion of these loads. W e are a l so i n t h e
process of rev is ing some of our pump systems on the load.
explained below, a l l the tubes that we have had on l i f e t e s t s have f a i l e d
eventually from window punctures or window cracking.
a l l tubes t h a t f a i l e d on l i f e t e s t had bad windows a t t h e time of f a i l u r e .
It has been observed t h a t the ion-type pumps on the load system are apt
t o s t a l l during t e s t s .
procured i n an attempt t o remedy t h i s s i t ua t ion . Diffusion-pump systems
are a l so being b u i l t .
A s w i l l be
That i s t o say,
Accordingly, some new ion-type pumps are being
D. LIFE TESTS
A t present we have one modulator operating 24 hours a day, 7 days
Under these conditions, counting breakdowns and change of tube a week.
and equipment, we accumulate approximately 500 t o 600 hours operating
t i m e per month. In general, t he l i f e t e s t i s being run a t approximately
one-half of r a t ed maximum power o f the klystrons:
peak, 10-to-12 k w average, 360 pps, 3 psec pulses. Under these conditions
we have had one tube operat ing f o r 600 hours and several tubes exhib i t ing
f a i l u r e s a t between 50 and 200 hours. It i s d i f f i c u l t t o determine a t
the present time i f the f a i l u r e s are due e n t i r e l y t o the tube o r a re due
i n p a r t t o the t e s t equipment i t s e l f . A s mentioned above, it i s rather
frequent f o r the load vacuum t o de te r iora te rapidly t o t h e point where
ion ic pumps s ta l l .
f o r these pumps, it was not p r a c t i c a l t o make immediate changes i n t he
c i r c u i t r y t o introduce in te r locks between the load vacuum and the modu-
l a t o r operat ion, This has been accomplished now, but the in te r locks
have not been i n operation long enough t o permit evaluation of t he new
operating conditions.
cathode bushing, but it i s probable t h a t t he bushing f a i l u r e followed
t h e f a i l u r e of t h e window and the consequent de t e r io ra t ion of t h e vacuum
on the tube side.
between 10 and 12 Mw
Because of' the design of some o f t he power suppl ies
In severa l cases we have found a punctured taube- '
I n most, i f not i n a l l , cases of window failures there seems t o be
a simultaneous loss of vacuum i n the load, A t t he present t i m e t he
instrumentation i s not good enough t o determine if the lo s s of vacuum
i n the load precedes the window f a i l u r e o r i s a r e s u l t of it. I n the
fu ture we hope t o be ab le t o devise a system by which we can determine
- 33 -
1
VI.
whether t he load vacuum deter iora tes f o r o ther reasons, o r i f an elec-
t ron ic a c t i v i t y a t t h e window surface produces a l o c a l de t e r io ra t ion of t he vacuum which then enhances Xhe chances of window puncture, breakdown
and cracking,
It must be s t a t e d at, t h f s point t h a t we have also had window f a i l u r e s
on the bepyl l ia -d isk windows that, have been used i n t he Zasr three tubes
operated under l i f e - t e s t , conditions"
E o EXPERBCEJTi'AE J'UBES
A t the present time we are runcing t e s t s on experimem,81 p!emanent-
To date w e have t e s t e d two tubes i n one permanent magnet-focused tubeso
magnet. The f i rs t t u b e t e s t e d with a permanent magnet had f i r s t been t e s t e d on the Plectromagnet and operated with an effiefeutcy of appsoxi-
mately 30$0 Once i n s t a l l e d i n the permanent magnet,,, t h e effic.ieney
of t h i s tube (bopped t o between 10 and 2.27&
ef f ic iency w a s caused by an inadequate shielding of the s t r a y f i e l d from t he permanent magnet i n the eathode region,
on shielding i n the gun region sf" t he klystron resulted i n much mope
s a t i s f a c t o r y r e s u l t s f o r t h e second tube t e s t e d on the permanent magnet.
In t h l s case, t he e f f i c i ency was about 32% with electromagnet and about
22% on permanent magnet. A r a the r s t a r t l i n g f a c t about t h i s t u b e , how-
This drastic decrease f n
The addit,fonal work done
ever, i s t h a t with the pemanenb; magnet t he gain i s higher and the
maximum e f f i c i ency o c c w s a t a dr ive much lower tnan %hat whieh w e had
measured with the eieet,romagnet,. In other words, at vpry low dr ives the
permanent-magnet tube appears to behave b e t t e r than what we had obsel-ved
with electromagnets, although we had attempted t o dupPfcata6;. the f i e l d
of the permanent magnet as closely as poss jb le with e2ectmmagneten On
the o ther hand, t h e permanent magmt would not; permit the?. sa tura t ion
e f f ic iency t h a t w a s observed w i t h t h e electromagnet wider supposedly the
same magnetic-field condi t icns e There are several. poss3bl-e expianations
f o r these d i f f e renc r s i n behavior, and these w i l l be irivesteigated during
the next quar te rs .
F. PLANNING THE KLYSTRON PROCLlffEMEhT
It is o w hope t h a t a prs?d:ictlon contract f o r %he procurement af
klystrons f o r use on t e s t scands and on t h e two-mile accrelcrat,or can be
- 34 -
VI "
signed during the calendar year 1962. plans on t h e numbers of tubes needed and the approximate schedules at
which these tubes must be procured,
plement of tubes needed f o r t he accelerator (240 p lus about 10% spares) ,
a la rge number o f klystrons will be needed f o r tests of t he tubes them-
selves and f o r other components.
Accordingly, we have begun making
I n addi t ion t o the i n i t i a l com-
If t h e present estimate of 2000-hours l i f e f o r t he klystrons operati-
ing on t h e acce lera tor proves val id , the t o t a l number of tube replace-,
ments per month w i l l be between 80 and 90. Plans w i l l soon be made t o
prepare f o r t he acceptance o r r e j ec t ion of tubes t o f u l f i l l a l l of these
requirements r /
G. KLYSTRONS ON MARK IV Two klys t ron tubes are now being used on the Mark Iv acce lera tor ,
The power output from these tubes i s approximately one-half o f w h a t we
had measured under t e s t conditions.
not c l ea r , bu t appears t o be caused by inadequate instrumentation,
An attempt t o reconci le t he da ta i s being undertaken with the help of
t he k lys t ron group.
The reason f o r t h i s discrepancy fs
.
- 35 -
VII.
V I I , HIGH-POWER KLYSTRON WINDOWS
A. WINDOW-LIFE TEST STAND
The l i f e - t e s t un i t has been operated about 250 hours during the
las t quarter , with s i x windows under tes t . Most of the time it w a s below
6 Mw, l imi ted by 'breakdown i n the pressurized sec t ion between t h e tube
and the f irst window, Tiis has been t raced t o moisture i n the freon
and t o a mismatch a t the f i rs t window,
a t 9 Mw but it has been unre l iab le .
bu t does not leak, a t t he same sec t ion where a window was damaged Last
quar te r .
Some operation has been obtained
One more window has been punctlared,
Hours on these two windows were 65 and 120 respect ively.
The new tr igger-generator units a r r ived from Ling during the quarter,
and t h e operation of t he modulator has, i n general, been sa t i s f ac to ry
s ince t h e i r i n s t a l l a t i o n o One of t he Li t ton type-L 3302 klystrons had
t o be removed because of a rc ing a t high-power l eve l s . The second tube
i s now i n use.
of t he Mark V klystron on t h i s system. This w i l l enable us t o t e s t
windows above the 10-Mw l i m i t s e t by the Li t ton tube. W e are s t i l l
awaiting a r r i v a l of add i t iona l power suppl ies so t h a t t he number of
windows under tes t can be increased t o twelve.
A new power combiner is under construct ion t o allow use
B. RECIRCULATOR WINDOW TESTS
The following t e s t s have been made on t h i s equipment during Lhe
pas t quar te r II
1. Half-Wave Disks
Two more half-wave d i sks have been t e s t e d , The f irst d i sk (No. 4) was i n a s t ruc tu re s l i g h t l y modified from Fig. 6gb) of the last S ta tus
Report,' The 2.875-in0 d iamregion w a s lengthened t o remove the window
f a r t h e r from t h e tapered region,
surface i n t h i s geometry, bu t developed seve ra l holes on the circum-
ference due t o poor contact with the metal. w a l l s ,
t e s t e d i n the o r i g i n a l geometry; t he failure was much l i k e t h a t shown i n
Fig. 7 ( I ) i n the last S a t u s Reportog
The window did not break down on the
This d i sk f a i l e d when re -
The second d i sk (No . 6) was t e s t ed
'Status Report, M Report No. 280, Project M, Stanford University, Stanford, California, October 1.961, p. 29.
'M-280, op. c i t , , p. 30a
- 36 - t
V I I .
i n t8he o r i g i n a l s t ruc tu re and f a i l e d on the generator side w i t h t h e
pa t t e rn shown i n Fig. 8. When reversed, it showed some breakdown but
quickly s t a b i l i z e d and operated normally.
haw f a i l e d on the source s ide and two have f a i l e d on t h e load.
So far, th ree of these disks
These th i ck d isks are the only types on which we have obtained
consistent, surface punctures.
w a s confined t o t he region of f a i l u r e ,
OCC"UI"E seems a matter of chance.
cussed above) it seems as i f the geometry i n the neighborhood of the d isk
is important. The "clean up"
of a Stanford and a Sperry window (see below) lends support t o t he idea
t h a t f a i iwe results from the right circumstances and i s immediate, and
t h a t gradual de t e r io ra t ion does not occur.
2 Sperry Thick-Disk Windows
These were similar i n construction t o the J-type,"
In a l l cases t h e a c t i v i t y t ha t w a s v i s i b l e
So far, the s ide on which puncture
On the basis of one t e s t (No. 4, d i s -
Further t e s t s a re planned t o check th i s .
--
except t h a t
the disk of AD995 i s .640-in. t h i ck ins tead of .125 i n . The t r a n s i t i o n
from cy l ind r i ca l t o rectangular waveguide i s a l so much less abrupt.
Three of these windows were t e s t ed . One f a i l e d a t less than 1 M w ,
apparently due t o poor construct ion at t h e metal-to-ceramic seal since
breakdown occurred i n t h i s region.
time at. approximately 27 Mw when rf breakdown s t a r t ed .
was no v i s i b l e evidence of t rouble , t he l e v e l of breakdown slowly de-
creased until it s t a b i l i z e d a t 8 Mw. This cycle was repeated several
timeso The t h i r d window had an ea r ly period of v io len t a rc ing during
which some punctures occurred (as i n the half-wave windows). It then
s t ab i l i zpd and operated normally.
3. One-Sixteenth-Inch Disks
One addi t iona l 1/16-in0 d isk of Coors AD 96 w a s t e s t ed .
The second window ran f o r a short
Although there
It operated
normally at t h e highest power avai lable .
Mark 111 acce lera tor by operation w i t h sudden turn-on a t high power and
poor vacuum were a l s o unsuccessful.
Attempts t o simulate damage on the
"Status Report, M Report No. 272, Project M, Stanford University, Stanford, Cal i fornia , July 1961, p . 16.
- 3 7 -
V I I .
FIG. 8--Half-wave disk No. 6 .
FIG. 9--Failure of beryllia window. - 38 -
4. Calorimeter
The r ing was used b r i e f l y f o r t e s t s on a dry calorimetric type of power meter.
f s o Photographic Work
A considerable e f f o r t was made t o improve the photography of events
f n the r ing . In pa r t i cu la r , an attempt was made t o co r re l a t e the fo r -
mation of holes w i t h "stars" occurring on the operating window.
was unsuccessful w i t h t he present equipment.
ment that w i l l be su i t ab le ,
camera t o take sequent ia l p ic tures of breakdown.
This
We are invest igat ing equip-
We a l s o hope t o be able t o use an ex i s t ing
6. Increased Ring Power
Some of t he equipment t o increase r ing power is now complete.
remainder should be here ear ly next quarter. We now plan t o use a
Liitton type-L 3302 on t h i s un i t .
The
c o OTHER WINDOW WORK
1, Resonant Cavity Tests
A series of tests w a s run w i t h t h i s apparatus using the Raytheon
5586 magnetron as a dr iver ,
much t o be desired, these tests showed t h a t the loading i n the cavi ty
w a s very heavy,
d r ive r ,
i n a very strange manner and i s not understood.
occurred on t h e surface of t he d i sk during these tests.
the cavi ty behaved i n a normal manner. We are now making arrangements
t o dr ive the cavi ty from a VA-87 Klystron using a s m a l l modulator bor-
rowed from the Hansen Labs.
2* X-Band Power
We have recent ly detected X-band frequencies i n both the resonant
Although the s t a b i l i t y of the system l e f t
Tests were a l so made using the more s t ab le VA-87 r ing
The loading of the cavi ty as a function of power input behaved
A very b r igh t discharge
Without the disk,
cav i ty and t h e resonant ring.,
whether t h i s power w a s from the dr iving tube o r being generated i n the
t e s t s t ruc tu re , The use of a General, E lec t r i c Company Pow-pass f i l t e r on the r i n g has reduced the amplitude by more than 20 db. W e are now
inves t iga t ing i f the remaining X-band power may be due t o nonl inear i ty of
window s t r u c t u r e s o
In both cases there w a s not c l ea r evidence
VII.
3. Mark III Window Fa i lu re s
Another window recent ly f a i l e d on t h i s accelerator . This makes
three s ince last July, i n cont ras t w i t h t h e former r a t e of 6.6 per month.
We are s t i l l unable t o dupl ica te these r e s u l t s on r ing tests. 4. B e r y l l i a Windows
Two b e r y l l i a d i sks have f a i l e d on Mark V kiystrons. These were at
l e v e l s of about 6-kw average and 6-rJfw peak powers.
by vacuum pump f a i l u r e , so it. i s not known i f high pressure may have
caused these. In the one window t h a t has been examined, there w a s a
l a rge crack plus punctures ident , ieal i n appearance t o those i n alumina
disks (see Fig. 9 ) . These w e r e 2 ,5 i n . i n diam and,200 i n , thick,
mounted i n the s t ruc tu re shown i n Fig. PO.
Both were accompanied
t r a n s i t i o n t o rectangular guide Ic--e
FIG* lO--Beryllia window assembly.
VI11 0
V I I I . MODULATOR STUDIES
A. PROJECT DEVELOPMENT ACTIVITIES
1. Igni t ron Studies During the Past Quarter
During the pas t quar te r we have t e s t e d two versions of t he 2-3233
ign i t rons , one with and one without a splash b a f f l e .
concluded t h e s e r i e s of t e s t s on these tubes, we have found t h a t the
2-5233 with b a f f l e does indeed perform well as a pulse modulator up t o
120 kw of average power. This r e s u l t ind ica tes t h a t our previous un- sa t i s f ac to ry t e s t s with t h i s tube were the r e s u l t of a f a u l t y tube r a the r
than a bas i c design e r r o r ,
While we have not
During the pas t quar te r we have a l so shown t h a t the 2-5234 with
splash b a f f l e operates very s a t i s f a c t o r i l y a t a 60-cycle pr f on the
Mark IV i n s t a l l a t i o n , where t h e tube i s switching two networks i n
p a r a l l e l and passing 8 , 0 0 o - ~ p , 3-psec pulses ,
Complete d e t a i l s of the t e s t r e s u l t s on t h e 2-5233 and 2-5234 w i l l
be compiled and published as soon as possible .
In addi t ion t o the studies mentioned above, we are cur ren t ly t e s t -
ing a new sample of an ign i t ron constructed i n accordance with our
Drawing 304-911,ll For t e s t purposes t h i s tube i s being cooled i n a
constant-temperature o i l bath, r a the r than a water jacket .
2 (I Application of Sol id-s ta te Diodes
During the pas t quar te r w e have encountered a s e r i e s of f a i l u r e s
In of so l id - s t a t e u n i t s used f o r c l ipper and hold-off diode service,
pa r t i cu la r , we are unable t o t r a c e the hold-off diode f a i l u r e t o any
c i r c u i t cause, We have conducted an extensive s e r i e s of t e s t s on our
c i r c u i t r y i n cooperation with Westinghouse E l e c t r i c Company, which
furnished the diodes; it concurs with us t h a t t he f a i l u r e i s due t o the
diode i t s e l f , r a the r than t h e c i r c u i t . The Westinghouse Company i s
present ly attempting t o f i n d a solut ion for t h i s t rouble ,
3. Invest igat ion of Sol id-s ta te Switches
Tests conducted on t h e 5,OOO-amp, 2-kv switch during t h e pas t
per iod have not been very promising. The u n i t furnished t o us by
"The tube cur ren t ly being t e s t e d i s the shor te r version of the two, and we expect t o know i t s behavior by approximately December 27*
- 41 -
VIII,
ShockLey Trans is tor Corporation f a i l e d a f t e r a few pulses at l o w currents .
This phase of t h e program i s being deferred u n t i l a l a t e r date.
4, I n order t o accommodate some high-power rf t e s t i n g t h a t i s required
Additional Ac t iv i t i e s of t h e Modulator Development Group
by t h e Accelerator S t ruc tures and Vacuum Groups, t h i s department i s
preparing t o move our ex i s t ing high-power t e s t laboratory equipment t o
another area s t a r t i n g about Deceniber 27., order a new 120-kw power supply t o replace our present u n i t and are
making necessary arrangements t o t u r n over enough equipment t o furnish a complete working modulator t o t h e Accelerator S t ruc tures Group.
We have accordingly placed on
- 42 -
IX .
IX. VACUUM SYSTEM
A. MARK IV CONVERSION
The Mark IV vacuum system was held under vacuum f o r the e n t i r e
quarter a t 3 x t o r r . Radiofrequency power w a s s t a r t e d during t h i s
t i m e and also some outgassing of the klystron area system. After the rf
power was run through the klystron waveguide, t ha t vacuum level. reached
7 X lomtb t o r r .
not enough t o outgas the tubes completely. The accelerator-tube vacuum
i s present ly holding a t 3 x t o r r . Further rf-power processing should
outgas the acce lera tor tubes and reduce the vacum leve l . The accelerator
tubes have a very la rge surface area and require a la rge amount of rf processing t o outgas them.
The accelerator tubes saw a small amount of rf power but
B. FEASIBILITY STUDIES Another vacuum equipment manufacturerss inspection t r i p was made.
The manufacturers were acquainted w i t h t he vacuum requirements of the
pro jec t and a means of f u r t h e r communication was established.
C. PROBLEM STUDIES 1. Sixty f t of waveguidewere evacuated and the pumping speed a t 20,
Further outgassing of the waveguide is necessary 40 and 60 f t measured.
and a check of the da t a w i l l be made.
2. The equipment f o r outgassing s tudies was fabr ica ted and run.
Eight d i f f e r e n t cleaning procedures were checked f o r t h e i r outgassing
e f f e c t on 304 s t a i n l e s s s t e e l .
cha rac t e r i s t i c s of d i f f e ren t materials.
Next we w i l l check the outgassing
3. The automatic bakeable high-vacuum valve has been fabricated
and i s ready f o r t e s t i n g .
ing torque and found t o be a s follows:
The gasket s ea l s have been checked f o r sea l -
Indium 3 f t - lbs
Gold 5 f t - lbs
Aluminum 5 f t - l b s
Copper 7 f t - l b s
Because of t he disadvantages encountered i n the use of In, Ag and Cu,
w e a r e using Al gaskets f o r the t e s t valve.
- 43 -
IX.
4. Molecular s ieve t r a p s a re being fabricated and checked so
t h a t t h e t r a p dimensions and operating cha rac t e r i s t i c s can be determined.
5 . The new meta l l ic gasket and flange system w a s operated satis-
f a c t o r i l y i n 1, 2, 3 and 4-in. s izes , but did not work i n the 6-in. s ize .
The system is being redesigned and reworked f o r fu r the r tes t ing .
6. A tes t pump stand is being fabr ica ted t o start t h e various
vacuum-equipment evaluations needed p r i o r t o se l ec t ing equipment f o r use
on Project M.
D. CONCLUSIONS The Mark I V vacuum system operated successful ly f o r the e n t i r e quar-
t e r . Radiofrequency power processing improved the vacuum leve l , but
f u r t h e r processing i s necessary.
The research s tudies necessary f o r determining the outgassing of mater ia l s , the valve, f lange and pumping systems t o be used on the
p ro jec t are progressing s a t i s f a c t o r i l y .
A study t o ready the design of the molecular s ieve t r a p f o r produc-
t i o n i s underway and should provide useful da ta i n t r a p e f f i c i enc ie s .
The program t o provide information i n the evaluation of avai lable
vacuum equipment has been started.
X.
X. SUPPORT AND ALIGNMENT
A. SITE EARTH-MOVEIVENT STUDIES
The r e s u l t s of the several e levat ion surveys t o date a re inconclusive.
The apparent var ia t ions in t h e elevation of ce r t a in points of the survey
are possibly within the accuracy of t h e surveying technique.
surveys a re t o be performed. Some new surveys w i l l cover the en t i r e
s i t e ; o thers w i l l be l M t e d t o the region of indicated uncertainty.
A permanent three-legged hydraulic tilt meter has been in s t a l l ed
Additional
a t t he s i t e i n the v i c i n i t y of the apparent var ia t ions i n elevation.
Some d i f f i c u l t y has been experienced i n cor re la t ing the observations of
the tilt meter t o those of the survey. It i s hoped tha t these d is -
crepancies w i l l be resolved as more observations a re made.
The new schedule for the s t a r t i n g of the t r iangula t ion and tri-
l a t e r a t i o n surveys i s s e t f o r January.
survey have been completed.
t o a r r ive soon.
The permanent monuments fo r t h i s
The last of t h e required equipment i s due
B. SUPPORT
Invest igat ion of the poss ib i l i t y of the use of a f o r t y - f t , simply-
supported acce lera tor substructure has continued.
been given t o the e f f e c t s of transverse forces on such a s t ructure .
Forces on t h e waveguides, due t o d i f f e r e n t i a l motion of the klystrons
r e l a t i v e t o the acce lera tor substructure, have been estimated. Fr ic t ion-
l e s s couplings f o r a t taching adjacent substructures t o allow f o r thermal
expansion have been proposed. Aluminum, s t a in l e s s s t e e l and m i l d s t e e l
have been considered as mater ia ls from which the substructure might be
fabr ica ted . Financial ly , aluminum and s t a in l e s s s t e e l a re nominally
Consideration has
equivalent. The cost of the mild-steel substructure would be much l e s s ,
However, the magnetic propert ies of the mild s t e e l may prevent i t s being
used.
C. ALIGNMENT
The proposed use of quadrupole-focusing magnets has introduced new
In addition t o the o r ig ina l alignment spec i f i - alignment requirements.
cat ions of s t ra ightness t o 63 m i l s i n any 330-ft length and 125 m i l s
i n the over-al l length, current spec i f ica t ions require that the center
of each quadrupole be within 5 mils of the two adjacent quadrupoles 250 f t away. A s t i g h t - a s t h i s - to l e rance
is, there is every p o s s i b i l i t y t h a t it can be accomplished through the
use of a proposed opt ical- tool ing system.
of a l i n e connecting the centers
- 46 -
XI.
XI. CONTROL SYSTEM STUDIES
A. GENERALSTUDIES
During the past quarter the Instrumentation and Control Group has continued general studies of the operation and maintenance requirements i
and of the costs and technical considerations that will influence the
control-system design.
1. Control Signals
Documentation of all signals and controls necessary for the opera-
tion of the accelerator is under way. The functions covered to date
include:
tion, beam extraction, and maintenance; (b) special transducer problems;
(c) automatic-protection requirements; (d) sector-control functions.
(a) measurement and control signals required for beam opera-
2* Central-Control Area
A conceptual-system-design proposal for central control of the accelerator was developed. Functional areas included in this design
are : (a) data communication between central control and accelerator
components, and (b) data handling and display within the central control
area. A budgetary cost estimate was prepared for a possible equipment configuration that is consistent with the design concept.
A study was completed defining assumed personnel-communication requirements for the accelerator and its control function, including
construction, maintenance, operation and administration demands. An
over-all system layout and an estimate for an installed cost per unit
was documented for telephone, order wire and service channels, public
address and intercom systems, and the power plants to support these
sys tems
One member of the group has,been making design studies for the
Microwave Circuitry Group during the past quarter.
A study of the trigger system is discussed in greater detail below.
B. DESIGN STUDIES
A detailed analysis of the shielding and grounding problems related
to the total Project M system is in progress. presented that resulted in a Ground and Shielding Committee being formed,
with representation from the Systems, Mechanical Engineering, Plant
An initial report was
- 47 -
XI 0
Engineering, and Instrumentation and Control groups.
1. Standardization of Connectors A study is in progress to determine the best types of connectors to
meet the project's requirements.
will be presented for each connector group when analysis and study are
completed.
Detailed standards and recommendations
2. Test-Stand Layout,
Layout of the cells f o r the test st,ands in the Test, Labura tdory
Building has been completed,
change over from an under-floor wiring system to an overhead Ztus-cluct4
system. Some time was spent in cost studies of the two systems.
The drawings were made on the basis of a
Block diagrams of tentative rf and focusing systems have been made.
A block wire-route diagram has been made of the rf system.
C. TRIGGER SYSTEN
1. Outline of System
The trigger system provides synchronization signals for the klystron
modulators, the sub-booster modulators, the gun and associated injection
pulses, monitoring and data-handling equipment, and other pulsed devices
in the accelerator,
However, it is clear that the trigger system must fulfill cert,ain additional special requirements:
a. The accelerator Jitter specification requires that the trigger
system have a jitter not over 5 nanoseconds. b Compensation for beam-loading effects will be provided t h rough
the trigger system,
c, Control of the rate at which AC-power consumption increases arid
drops is to a large degree determined by the trigger system. d. 24-hour operation requires that certain maintenance functions
and tests must be carried out in the interval between beam pulses.
e. Radiofrequency power must be withheld from the accelerator for
protection of windows in the event of gas bursts o r vacuum fa i lure ,
f. The gun must be curried off if the beam is misadjusted so as Lo
reduce hazard to equiprnen-t or personnel,
g. Multiple-beam operation on Project M must be contl-olled entirely through the trigger system.
XI 0
It should be noted that multiple beams will be used for operations,
whether or not they are used for physics.
routine-maintenance functions depend on using a form of multiple-beam
operation.
Steering,phasing and many
The following system is proposed as a first-order conceptual design,
A single high quality transmission line (10 Mc bandwidth or better) will carry initiation pulses at 360 pps from a master oscillator to local stations
The particular rate required at any station will be chosen by a
remotely-activated selector switch.
A gating circuit at each station will select the appropriate pulses and deliver them to a trigger booster that will reshape the trigger
pulse as required, The normal delay adjustments will be introduced
locally, The special delays for beam-loadicg adjustments also will
be introduced locally, by remotely controlled devices.
2. Basic Transmission System
The pulse-time jitter for the accelerator system as a whole has been
set at 15 nanoseconds, and for the trigger system itself must be of the order of 5 nanoseconds, The primary distribution lines for the trigger
signals must therefore have a bandwidth of about 200 Mc, trigger line should be a rigid, air-dielectric line much like the master
rf-drive line in order to:
equal to the beam velocity without cumbersome compensating networks;
(b) eliminate need for series-booster amplifiers in the trigger line;
(e) reduce delay-distortion of the signals; and (d) provide a stable
line that is not easily damaged. Only one such l i n e need be used,
The main
(a) make the effective trigger velocity
The main trigger line will carry a basic 360-pps signal, a 60-cps
signal for synchronizing a divider at each sector, and a I-cps signal
for single-pulse operation and for synchronization of the data-transmission
system.
purpose of kepping the A@-power load more constant.
The choice of a fixed 360-pps basic rate was made partly for the
If the repetition rate in the main line were variable only in steps of 60, 120, rates, the entire accelerator should thenbe turned - off before the repe-
tition rate could be changed,
360 pps, and all the klystrons operated at one of these
The rate of increase of power consumption
of the high-voltage supplies i s l imited t o 3-Mw s teps , 12 Mw/min,
r a t e of decrease cannot exceed 18 Mwlmin. ce le ra tor cannot be switched o n a t 60 pps (a 4-Mw s t e p ) , but the klystrons
must be turned on i n successive groups, To change from 240 t o 360 pps
requires turning of f groups of klystrons i n sequence, changing the r a t e
t o 360, and then turning them on by groups again.
take a minimum of 3 min.,
min,to switch from 60 t o 120 pps and 10 min.to switch from 120 to 360 pps,
The AC-power consumption fo r the high-voltage supplies must be reduced
t o zero before changing the r a t e , and then increased t o the desired l e v e l .
Using a bas ic 360-pps t r i g g e r s igna l and dividers a t each sector ,
the r a t e can be switched sector-by-sector d i r e c t l y t o the desired new
value, The operation w i l l take about half the time given i n the examples
above, b u t the beam w i l l suf fe r no in te r rupt ion a t a l l , The power C O G -
sumption w i l l change from one l e v e l t o the other without the intermediate
period of no load.
The
In Stage I, the e n t i r e ac-
The operation would
'In Stage T I , it would kake a m i n i m u m of 3-l/2
It w i l l be recognized t h a t a form of "multiple bean" operation e x i s t s
during the change:
lower rate; a port ion of the accelerator w i l l operate a t a higher r a t e
with a "zero-current" beam on the odd pulses ,
the normal beam w i l l continue t o be delivered a t the
3. Trigger Selector
The spec i f ica t ion t h a t the accelerator operate a t various pulse
r a t e s thus implies t h a t each sec tor a n d sub-booster be capable of opera-
t i n g a t a d i f f e r e n t r e p e t i t i o n r a t e ,
r a t e s s t i l l be appropriately synchronized, they must a l l be derived
from a s ingle pulse- t ra in from r,he master generator and a s ingle main
t r i g g e r l i n e .
t h a t passes pulses appropriate t o ,the desired r a t e and blocks the r e s t .
A sketch of the venting of the t r i g g e r pulses i s given i n Fig. 11,
Appropriate s e l e c t o r s w i l l subdivide the master t r i g g e r s igna l t o pro-
duce the desired r a t e for each component, The s e l e c t o r i s shown i n
somewhat more d e t a i l i n Fig. 120
Since it i s necessary t h a t all
The desired operating rate w i l l be obtained by a gate
The timing of the output pulses of any channel i s determined so le ly
by the basic 360-pps s igna ls and the individual channel-delay l i n e .
The purpose of the gate i s t o transmit selected pulses with m i n i m a l
- 50 -
XI.
pulse s e l e c t o r
Gun
* delay --. amplif ier ..Io Sub-Booster
- u n i t (Sector 2 )
Main t r i g g e r
l i n e (360 PPS)
Sub -Booster (Sector 1)
Modulator i g n i t o r s (Sector 1)
Modulator gr ids (Sector 1)
Auxiliary equipment (Sector 1)
Modulator ign i tors (Sector 2 )
Modulator gr ids (Sector 2)
FIG. 11- -Trigger pulse d i s t r i b u t i o n .
- 51 -
xl.
t -*360 PPS ~ 60 pps
divider : PPS
Main trigger transmission line
synch. separator
J
L trigger pick-off 3 for sector
I l l 60 PPS 6 phases
remotely operated select or switches
FIG. 12--Detail of selector unit.
( open 1 4 gate
- 1
- 52 -
c Y
l/
XI..
delay and t o block unwanted pulses (o r t o block a l l pulses when required
f o r l o c a l protect ion of equipment).
automatical ly c loses the gate. The gate i s opened by signals trans-
mit ted from the l o c a l d iv ider .
so that the i n t e r v a l between ac t iva t ion of the gate and the pulse t o be
t ransmit ted i s constant, regardless of r epe t i t i on r a t e . The delay
through the gate should therefore be unaffected by the r epe t i t i on r a t e .
The act ion of t ransmit t ing a pulse
The auxi l ia ry s igna ls a r e synchronized
Since a 360-pps r a t e w i l l be used fo r the master s igna l , uniform
pulse r a t e s o f 60, 120, 180, and 360 w i l l be possible .
300 o r 240 pps could be obtained by skipping one o r two out of every
s i x pulses . For the sake of f l e x i b i l i t y and f o r ease of maintenance,
it i s proposed t h a t a t each sec tor a separate t r i g g e r r a t e se lec tor and
delay u n i t be provided f o r the klystron modulators, f o r the dr ive sub-
booster and f o r any aux i l i a ry equipment. In order t o prevent dropping
the PG and E load i n case of f a i l u r e of the master t r i g g e r generator
of the t r i g g e r l i n e , the se l ec to r switch w i l l a l so determine the rate
of a stand-by generator a t each sector t h a t w i l l continue t o pulse the
klystron modulators a t the same ra t e , should the master t r i gge r f a i l
t o a r r i v e .
A pulse r a t e of
The sec to r s would no longer be synchronized under such stand-by
operat ion, and the beam would disappear, bu t the AC power could be r e -
duced i n an order ly manner.
The master t r i g g e r w i l l consis t of two pulses of opposite po la r i ty ,
one of which w i l l be used t o f i r e the modulator i gn i to r s , and the second
t o t r i g g e r a l l o ther equipment. The delay adjustments need operate only
on the second t r i g g e r s igna l . In general , most channel-delays can be
p r e s e t by l o c a l screwdriver adjustments. The var iab le delay required
t o compensate fo r beam loading must be control led by the beam operator,
b u t can be introduced a t the t r i g g e r booster by remote control . A t
each modulator, spec ia l c i r c u i t r y i s provided t o delay the klystron
pulse 5 psec l a t e r than normal ( s t i l l within the r f -dr ive pulse) f o r
stand-by warmup and fo r t e s t ing , o r t o delay the pulse 10 psec (outside
the r f -dr ive pulse) i n case o f gas bu r s t o r vacuum f a i l u r e .
l a y s w i l l be ac t iva ted by l o c a l o r automatic manual control .
These de-
- 53 -
XII.
X I I . RESEARCH AREA DESIGN
A. WORK COMPLETED
1. Gas Scattering12
We ca lcu la ted t h e beam loss i n the acce lera tor a r i s i n g from single
s c a t t e r i n g from an exponentially-screened Coulomb f i e l d . We considered
two cases of r a d i a l focusing: none a t a l l , and a very crude version of
r a d i a l focusing. Each case yielded approximately the same answer, namely,
a loss i n beam current of 0.05% at a pressure of lom5 mm Hg. The radia-
t ion-source s t rength a r i s i n g from t h i s beam loss i s about 100 times less
than we usual ly assume i n our shielding calculat ions.
t h e t o t a l beam power absorbed i n the machine as 3% of t h e f i n a l beam
power E I ) . We gave some arguments t h a t ind ica te t h a t multiple scat-
t e r i n g i s unimportant i n the machine because t h e t o t a l amount of Scat-
t e r i n g ma te r i a l i s so s m a l l .
(Usually we take
f f
2. Activation of t he Cooling Water
A t t h e suggestion of W. L. Gallagher we estimated the formation of
chemical a c t i v i t y and rad ioac t iv i ty i n t h e cooling water as it passes
through t h e water jacket next t o the machine,
ac t ive chemical molecules i s about 1 p a r t per mi l l ion per day (assum- ing 1 ac t ive molecule per ion p a i r ) .
l e v e l i s low enough so t h a t we do not plan any fu r the r work.
radioact ive nuclide we considered was O1'.
3 O ; O O O gal lons of water w a s 70 cur ies .
ser ious hazard because of t h e shor t h a l f - l i f e (2 .1 min ) .
t h a t t h e infrequent formation of a nuclide with a long l i fe t ime, e . &. , G I 6 ( 7 , 3p2n) C l l o r a (7 ,n) reac t ion on an impurity, might give r i s e
t o a more important hazard.,
The r a t e of formation of
The ca lcu la t ion i s rough, but t h i s
The only
The sa tura t ion a c t i v i t y i n
This does not seem t o be a
It i s possible
Bo CURRENT INVESTIGATIONS
1. Radial-Shower Development
Equipment i s being constructed by J. Cobb t o measure radial-shower
development a t 1 Bev.
under t h e d i r ec t ion of R. Hofstadter. It i s similar t o a measurement
T h i s work i s being done on the Mark I11 acce lera tor
l2H0 C. DeStaebler, J r . , "Scat ter ing of Beam Electrons by Residual Gas i n t h e Accelerator,' ' M Report No. 281, Project M, Stanford University, Stanford, Cal i fornia , October 1961.
- 54 -
XII.
made a t 187 Mev by Kantz and Hofstadter.13
check of a radial-shower development calculat ion now being done by
C. Zerby a t Oak Ridge.
This w i l l allow a b e t t e r
2. Induced Act ivi ty
We are completing a calculat ion of the radiat ion l e v e l i n the ac-
ce le ra tor tunnel when t h e beam i s of f t h a t a r i s e s from the decay of
nuclides made when t h e e lec t ron beam h i t s the accelerator .
An important experimental check of t h i s calculat ion w i l l be made
through t h e kind cooperation of G. Friedlander of Brookhaven National
Laboratory. During the course of the experiment on radial-shower develop-
ment ( see B.l. above) we w i l l i r r a d i a t e some copper f o i l s at d i f f e r e n t
depths i n t h e shower, and Dr. Friedlander w i l l analyze these radiochemically
for us.
3. Shielding Calculations at Oak Ridge
Shortly (within one month) we expect t o receive the r e s u l t s of the
one-dimensional nuclear-cascade calculat ion from Oak Ridge. The calcula-
'cion gives t h e energy spectrum of nucleons and pions as a function of
depth i n a t h i c k shield.
t ranspor t equations f o r neutrons, pro-tons and charged pions. These four
coupled i n t e g r o - d i f f e r e n t i a l equations are solved numerically on a com-
puter . Then the at tenuat ion calculat ion w i l l be combined w i t h a source
of p a r t i c l e s based on Dedrick's calculat ions of the y i e l d of photo-pions
and photo-nucleons from t h i c k t a r g e t bremsstrahlung, and t h e rad ia t ion
l e v e l outs ide of the e a r t h sh ie ld around the accelerator w i l l be ca l -
culated.
The problem i s formulated i n terms of the
Another ca lcu la t ion at Oak Ridge, which i s j u s t ge t t ing s ta r ted ,
concerns t h e la te ra l development of the electron-photon cascade shower,
and eqpecial ly t h e influence of spec ia l geometrical boundaries on the
shower development.
the design and evaluation of coll imators, posi t ron rad ia tors and energy-
def ining s l i t s .
The r e s u l t s of t h i s ca lcu la t ion w i l l be usefu l i n
13A. D. Kantz, "Electron-Induced Showers," HEPL Report No. 17, W. W. Hansen Laboratories of Physics, Stanford University, Stanford, Cal i fornia , May 1954.
- 55 -
r .
X I I .
4. A t CERN, nuclear emulsions were exposed under different depths of
High-Energy Absorption Mean Free Path
baryte concrete (maximum depth 1750 gcmm2) t o a beam of 21-Bev protons.
Some of the emulsions are being scanned for us by the emulsion group
under Gilbert and Oliver at the Lawrence Radiation Laboratory (Evermore),
and the scanning i s almost completed. This experiment gives a d i r ec t
measurement of the fluxes of par t tc les a t large depths i n th ick shields.
3 - Transverse Shielding
a. We are collecting information on a l l aspects of the shielding
along the accelerator so tha t we can evaluate the requirements more
accurately.
appreciably o m conclusions i n M=-262.14
shield of d i r t 35-ft th ick gave a radiation l eve l a t the surface of the
shield tha t i s about 10'' times radiation-worker tolerance and a l e v e l a t
a distance 500 f t from the machine t h a t i s about .02 times t h e general-
population tolerance.
amounts. For the general-population l eve l we estimated tha t the uncertainty
factor w a s about 50.
So far we have not encountered any information tha t changes
There we found that a uniform
Both of these leve ls are uncertain by large
In our next report we w i l l use t he r e su l t s of the Oak Ridge Monte-
Carlo calculations on the diffusion and absorption of 1-19 Mev neutrons
i n the atmosphere. These calculations, which were completed recently,
give an idea of the e f fec t of the ground on the f lux leve ls at t h e
ground-air interface f a r from the source.
b. Some additional calculations have been made on the neutron f lux
t o be expected on the face of the transverse shield. The neutron-source
f lux considered is taken t o be given by combining the soft-shower photon
spectrum w i t h the deuteron model f o r the nuclear photo-effect as described
previously. l5
of several thicknesses t h a t are constructed e i the r of ear th o r ordinary
concrete.
ly , and t h e r e su l t s give the spectrum of neutrons expected at any point
on the face of the shield. These spectra show a peak i n the neighbor-
hood of 300 Mev and have been integrated t o obtain the t o t a l f lux
The resul t ing photoneutrons are then attenuated i n shields
Oblique and normal attenuation fac tors are considered separate-
14H0 C. DeStaebler, Jr,, M Report Noo 262, " A Review of the Trans- verse Shielding Requirements f o r the Stanford Two-Mile Accelerator," Project M, Stanford University, Stanford, California, April 1961.
M Report No. 227, Project M, Stanford University, Stanford, California, October 1960.
"K. G. Dedrick, "Deuteron Model Calculation of Photonuclear Yields,"
T 1 .
expected a t any point on the shield.
l i t t l e from t h a t reported i n ~ - 2 6 2 , ~ ~ except t h a t a more de ta i led explora-
t i o n of t h e problem has been worked out.
i n an M repor t i n t h e near future .
In general, t h i s work d i f f e r s
The r e s u l t s w i l l be published
6. Skyshine
A repor t i s t o be published soon giving a formulation of t he s ingle-
s ca t t e r ing model for slryshine problems. I n the method used, shielding
h i l l s can be e a s i l y considered. T h i s work is expected t o be usefu l i n
lay ing out designs for the end s t a t i o n i n a rough manner. Eventually,
t he much more accurate (and more expensive) Monte-Carlo techniques must
be applied, but it i s he lpfu l t o ru l e out c e r t a i n p o s s i b i l i t i e s i n i t i a l l y ,
16~-262, op. c i t .
- 57 -
XIII.
X I I I . SITE, BUILDINGS AND UTILITIES
By t h e end of t he calendar year t h e e f f o r t on S i te , Buildings and
U t i l i t i e s design had reached a r a t e of 60 men/day.
t i o n e f f o r t w a s rescheduled t o coincide with the a v a i l a b i l i t y of con-
s t r u c t i o n funds, now estimated a t February 15, 1962.
The f irst construc-
A document e n t i t l e d "Project M--General Development Plan f o r Con-
This plan i s t o be vent iona l F a c i l i t i e s " was d i s t r ibu ted i n November.
used as a general guide i n scope, schedule and budget f o r a l l t he f a c i l i t i e s
t h a t a r e t o be constructed and t h a t a r e not p a r t of the accelerator , i t s auxiliaries, o r p a r t of the research equipment. A s design progresses
t h e p l an w i l l be revised t o r e f l e c t t he l a t e s t planning.
A. MAJOR CONVENTIONAL FACILITIES
The following i s a statement of t he s t a t u s of the major conventional
f a c i l i t i e s now under design.
1. S i t e Improvements
The loca t ion of t he entrance road has been se lec ted along Sand H i l l
Road.
improvements.
on t h e s i t e and i s preparatory t o the f irst bui ld ing construction.
T i t l e I design has been prepared for t h e first increment of s i t e
This increment i s the f irst construct ion work t o be done
2. S i t e U t i l i t i e s
T i t l e I design of the f i r s t increment of s i t e u t i l i t i e s has been
submitted.
system t h a t w i l l be j o i n t l y developed by Stanford University and The
City of Menlo Park.
Aqueduct .
Plans have become f i r m t o obta in high-quality water from 8
The source of water i s the l o c a l Hetch Hetchy
Preliminary negot ia t ions have been held with the AEC and the FG and E
Co. t o supply t h e pro jec t e l e c t r i c power.
of a 60-kv l i n e en ter ing the p ro jec t from Alpine Road appears firm.
This l i n e w i l l have a l imi ted capaci ty of approximately 15 Mva.
major source of power w i l l be a 220-kv l i n e t h a t w i l l e n t e r the project from t h e west end and be d i s t r ibu ted t o the acce lera tor a t 12 kv from a
subs t a t ion loca ted approximately a t the mid-point of t he accelerator .
The high-voltage l i n e w i l l l a te r be extended t o supply l a rge amounts of
power t o the End S ta t ion equipment loca ted a t the e a s t end of t he pro jec t .
Planning f o r t h e 220-kv l i n e has j u s t s t a r t e d .
Location and type of service
The
-. 5a -
Other u t i l i t i e s a r e being handled rout inely.
3. Test Laboratom Building
T i t l e I1 construct ion drawings were f inished. Construction b ids
w i l l be opened i n the middle of February.
bu i ld ing w i l l be f in i shed by t h e end of 1962, It i s an t ic ipa ted t h a t t h i s
4. Administrat ion and Engineering Buildinn
T i t l e I design has been f inished.
5 . Schematic drawings of t h i s complex of bui ldings have been approved
Shop and General Service Buildings
by t h e Board of Trustees of Stanford and are now being developed for T i t l e I submittal . Both t h i s complex of bui ldings and t h e Administra-
t i o n and Engineering Building w i l l be completed e a r l y i n the spr ing of
1963
B. SPECIAL PROBLEMS
Invest igat ion of t h e geology and t h e s t a b i l i t y of t he proposed
bui ld ing s i t e f o r the Accelerator Housing w a s continued.
of a small amount of s o i l movement has been measured near t h e west end
of the s i t e . Although t h e indicated amount of motion i s within t h e
design tolerance o f t h e acce lera tor alignment, t he motion i s ne i ther
wel l understood nor wel l documented. Studies a re proceeding i n t h i s
An indicat ion
area.
Plans were made for more temporary space t o house the pro jec t during
the construct ion period.
25,000 sq f t of warehouse-type space t o be temporarily used as o f f i c e
space. The new bui lding w i l l be i n t h e same general loca t ion as t he
present Project M Building on campus.
Stanford University w i l l supply an addi t iona l
- 59 -
-1 .
X I V . WATER SYSTEM
XIV.
A. PLANT WATER
The plant-water system w i l l be served by the expansion of the City
of Menlo Park 's system. T h i s system w i l l serve, besides Project M, a l l
Stanford lands i n $an Mateo County and a l l of the lands of t he Sharon
Es ta te development.
t o i t s share of the expanded system. 2,000,000 gal lons of water storage
w i l l be provided on Sand H i l l at Elev. approx 485 f t , 1,000,000 gal lons
being reserved for Project M use. Elev. 485 f t i s high enough t o pro-
vide adequate grav i ty f i r e - f i g h t i n g flow pressure. Plans and negotia-
t i o n s a re proceeding toward the i n s t a l l a t i o n of enough of the plant-
water system t o serve the laboratory area a t t h e t i m e t he T e s t Labora-
t o ry Building i s complete.
Project M w i l l pay a connection charge equivalent
B. COOLING WATER
There w i l l be th ree cooling-tower s t a t i o n s serving the p l an t :
one la rge one loca ted about halfway along t h e two-mile acce lera tor t o
serve t h e Klystron Gallery and Accelerator Housing, a second la rge one
located near t h e end s t a t i o n s t o serve them and the beam switchyard,
and a t h i r d and smaller s t a t i o n t o serve the bui ldings i n the laboratory
area. The las t named w i l l be constructed f irst , t o coincide with the
construct ion of the Test Laboratory Building.
The following arrangement w a s recommended i n ABA Report, "Heat
Transfer System Study" (ABA-3), for cooling the two-mile accelerator .
Cooling-tower water would be d i s t r ibu ted t o f i f t e e n i d e n t i c a l heat-
exchanger i n s t a l l a t i o n s spaced about 640 ft apar t along the length of
the acce lera tor . A t these points t h e low-conductivity, c losed-circui t
cooling-water systems serving klystrons, modulators, e t c . , w i l l give up
heat t o the cooling-tower water system. The heat would, i n tu rn , be
given up t o the atmosphere a t the c e n t r a l cooling tower. T h i s recom-
mendation w i l l be reviewed relat ive t o the p o s s i b i l i t y of having only one b i g c e n t r a l heat-exchanger i n s t a l l a t i o n r a the r than t h e f i f t e e n
described above.
In the case of the beam switchyard and end-station area, cooling-
tower water w i l l be d i s t r ibu ted t o heat-exchanger i n s t a l l a t i o n s located
- 60 -
XTV .
adjacent t o the major cooling-load centers where the exchangers w i l l
pick up the heat from the closed-circui t , low-conductivity cooling water.
The laboratory a rea cooling-water system i s i n . the de ta i led design
s tage.
The deionizers w i l l produce water of 500,000 ohms minimum specif ic
res i s tance w i t h an oxygen content of 0 . 1 ppn maximum.
C. BLOW-DOWN WATER
A study w i l l be made of the possible uses of t h e blow-down water
from the cooling towers.
and used for Project M lands i r r i g a t i o n and/or t o augment t h e water
supply t o Lake Lagunita.
There i s a p o s s i b i l i t y t h a t it could be stored
D. RESEARCH AND DEVE;LOR.TENT
See Section 111, Accelerator Structure Studies, f o r research and
development work on cooling t h e accelerator s t ruc ture .
xv. I
XV. HEATING AND VENTILATING
Detailed design of the heat ing and ven t i l a t ing system f o r the Test
Laboratory Building i s complete.
T i t l e I design f o r heating, ven t i l a t ing and a i r conditioning the
Engineering and Administration Buildings has been completed.
T i t l e I design f o r U t i l i t y Building A has been completed and de-
t a i l e d design s t a r t e d .
air-compressor equipment, air-conditioning r e f r ige ra t ion equipment, and
the emergency-power d i e s e l generator. The cen t r a l plant will serve a l l
of t h e bui ld ings i n t h e laboratory area.
T h i s bu i ld ing will house a central-heat ing plant ,
Yard piping i s being prepared i n a separate T i t l e I package.
ABA has completed a report e n t i t l e d , "Humidity i n the Accelerator
Housing" ( ABA-25) out l in ing a couple of a l t e rna t ives i n ven t i l a t ing
the Accelerator Housing.
- 62 -
XVS .
XVI. REVIEW OF CONTRACT WORK
A. EARLY ACCELERATOR WORK AT STANFORD The proposal t h a t led t o Contract AT(04-3)-21, Project Agreement
No. 1, w a s submitted t o the AEC by Stanford i n April 1953. A t t h a t
t i m e t h e Stanford Mark I11 a c ~ e l e r a t o r l ~ h a d been i n operation as a research vehicle f o r about 18 months. Although the operation of Mark IS1 at t h a t t i m e was generally sa t i s f ac to ry , c e r t a i n of i t s components and
systems did not funct ion su f f i c i en t ly w e l l t o produce maximum performance
and r e l i a b i l i t y .
Funding f o r t h e Stanford accelerator work p r i o r t o 1953 had been
provided primarily by Contract N6onr-25116, a j o i n t program of t he
Office of Naval Research and t h e Atomic Energy Commission, and i n 1953 most of these funds were being used t o support t h e program of high-
energy physics research with t h e machine.
p l a t e d a program of research and development a c t i v i t i e s which were in-
tended t o analyze and improve the Mark I11 acce le ra to r ' s operation, and
more broadly t o contribute t o the general area of accelFrator technology.
I n addi t ion , t h e scope of cont rac t work described i n t h e proposa1, and
incorporated i n t h e Contract t h a t began on Ju ly 1, 1953, c a l l e d f o r
"a study of t he f eas ib i l i t y of extending t h e l i n e a r e l ec t ron type of
acce le ra to r i n t o the multi-Bev range,"
t r a c t did not include a c t u a l development of such a l a r g e r macnine, which,
i f eventual ly proposed, was expected t o be funded separately.
The 1953 proposal contem-
The terms of t he o r i g i n a l con-
B. CONTRACT AT(04-3)-21, FROJXCT AGREEMENT' NO. 1
The spec i f i c p ro jec t s described i n t h e o r i g i n a l 1953 proposal were
t h e following :
ln Studies of apparent defec ts i n t h e Mark 111 acce lera tor , which
17 The Mark I11 acce lera tor , now operating at one Bev, i s described i n "Stanford High-Energy Linear Electron Accelerator,' ' by M. Chodorow, E. L. Ginzton, W. W. Hansen, R. L. Q h l , R. B. Neal, W. K. H. Panofsky, and t h e S taf f of the W . W. Hansen Laboratories of Physics, Review of S c i e n t i f i c Instruments, February 1955. b r i e f review of e a r l i e r accelerator work a t Stanford, and an extensive l i s t of references pe r t inen t t o the l i n e a r e l ec t ron accelerator f i e l d .
This paper a l so contains a
- 63 -
included l o s s of a subs tan t ia l f r a c t i o n of the in jec ted Seam current i n
the f i r s t t e n f e e t of the machine, improving the beam-eneqg spectrum,
and development of a more s tab le rf drive system,
2. Improved accelerator performance, which included redesign of
klystrons t o increase peak power output, %est3 of permissible voltage
gradients in the accelerator s t ructure , and s%udies of the propert ies of
acce lera t ing s t r u e t u r e s of d i f f e r e n t configurations
3. More r e l i a b l e compcments, which included development of a kly-
s t ron t h a t could be sealed-off" a f t e r evamation rat,her than continuously
pumped, and improvement of" the couplers tbro~zgh whfch the klystron power
w a s fed i n t o the accelerat ing struct,urc
4, Preliminary design of a lirrear e lec t ron a rce le ra tor f o r higher
energy (approximately 30 Bev)
d e t a i l the s ine, cos t , tolerances, probable charac te r i s t ics , e t c . , of
such a machine."
This l a t t e r st:idy was "t,c show i n some
A s an e a r l y p a r t of the contract program, Stanford constructed a
smalley acce lera tor , the 20-f"t Mark IU mach-fne, f o r use as the program's
primary t e s f , vehi_cle, This machine i s iocated i n t h e yowave Labor=-
t o r y of the W. W, Hansen Laboratorlea o f Physfcso
Many a s p c t s of 1 i n e a . r e l e y t r o n accelerator technology have been
invest tgated diuring the eight-year t e r m of t,iw con1,ract In thla b r i e f
summary, we shal-1 not attempt t o describe the s p x i f i c projects, since
this i s done in khe Status EeporfJs of t ,hc crotrraTt and i n t h ~ Technical
Reports and papers l ist ,ed i n Sec1,iori XdlT of r,ii;s F i n a l Report .
In b r x f , t=1e cont,iming work oi" %he rrorr;ract hhs l e d t o sii"itari%ial
imp~ovement i n the operat,ior! of the pr~ser ,s ai ,fnrd azceicraiors , i o
thy developmpnt of a large number of c~npo~!? F m d systems of" irnyroved
perfolqance and r e l i a b i l i t y , and to thr general tochnelugical experience
that, has been and w i l l eontirrue t o be n e c e 5 s a ~ j for %he design and con-
s t r u c t i o n of the fwo-mile accelerator ,
By 1953 it had hecome apparent %kat, the Mark 11-1 machine was proving
t o be a useful instrument for high-energy physlcs research, and during
1954 and 2-93? there w a s a ser tes of disciAsssons abo-;t and preliminary
s tudies of a multi-Rev machine based on the same pr inc ip les of" opexatlon.
A formal study group w a s created i n 1956, consis t ing ch ief ly of members
of t h e staffs of the Microwave ar,d High Energy ,Fhysics Laboratories.
A y e a r ' s work by t h i s group resu l ted i n submission t o t h e government
of a d e t a i l e d proposal for a two-mile-long accelerator i n April1957,
and a f t e r extensive review and some minor modifications the proposed
"Project M" w a s authorized by the Congress i n September 1961. t i o n i s expected t o begin ear ly i n 1962,
Construc-
The work of Contract AT(04-3)-21, PoA, 1, made the proposal f o r t h i s
l a r g e machine possible , In recognition of the changing character of the
Stanford accelerator group's a c t i v i t i e s a f t e r the proposal had been sub-
mitted, the scope of work of P.A. 1 w a s broadened, on August 31, 1960, t o include s p e c i f i c a l l y "s tudies and research relevant t o and/or useful
i n connection with the Multi-Bev Electron Accelerator project proposed
by the University t o the AEE f o r future construction."
f i c a t i o n , the work of the contract became f u r t h e r divers i f ied, as in-
dicated by Sections I1 through XV of t h i s Report, t o include many of
the aspects of design and development preliminary t o construction of
t h e la rge accelerator laboratoryo
With t h i s modi-
The Project M a c t i v i t i e s have a l so been supported, since September 1,
1960, by a second contract , AT(04-3)-363, which w i l l continue i n e f f e c t
through p a r t of 1962, will be funded by a new contract, AT(04-3)-400: which i s expected t o
begin e a r l y i n 1962+
Construction of the two-mile accelerator laboratory
- 65 -
XVII. REPORTS AND PAPERS
Below i s a l i s t of the Technical Reports and papers t h a t describe
the work supported by Contract AT(04-3)-21, Project Agreement No. 1.
The Abstracts of these documents a re given, when available, i n the f o l -
lowing pages.
i n the quarter ly Status Reports, which were issued by the Microwave
Laboratory, W. W. Hansen Laboratories of Physics, Stanford University,
Stanford, California, up u n t i l June 30, 1960. From July 1, 1960, through
t h e end of the contract , November 30, 1961, these S ta tus Reports have
been issued j o i n t l y by the Microwave Laboratory and by b o j e c t M, Stan-
f o r d University, Stanford, California.
Much of the technical work of the contract i s described
A. LIST OF TECHNICAL REPORTS AND PAFERS
Issued by t h e Microwave Laboratory :
R. L. Kyhl, " A Study of Multi-Bev Linear Electron Accelerators,"
M. L. Report No. 240, June 1954 (no a b s t r a c t ) .
E. A. Sm&rs, "Electron Orbits i n the Buncher of a Linear Accelerator,"
M. L. Report No. 252, April 1955 (abs t rac t on page 69 ) .
J. M. Ponce de Leon, "Design of the Bunching Section of the Stanford
Mark IV Linear Accelerator," M. L o Report Noo 265, June 1955 (abs t rac t
on page 70) .
R. L. Kyhl, "The Use of Non-Euclfdean Geometry i n Measurements of
Per iodical ly Loaded Transmission Lines," M. L. Feport No. 282, October
1955 ( a b s t r a c t on page 71 )
C. B. Jones and R. B. Neal, "Development of High-Power Modulators
With Low-Voltage Components," M. L. Report No, 288, December 1955 ( a b s t r a c t on page 72 ) e
E. A. Smgrs, "Prebunching by Velocity Modulation i n Linear Ac-
ce le ra tors , " M. L. Report No , 303, April 1956 (abs t rac t on page 73).
- 66 -
XVII.
R. B. Neal and W.K.H. Panofslry, "The Stanford Mark I11 Linear Ac-
ce l e ra to r and Speculations Concerning the Multi-Bev Applications of Electron Linear Accelerators," CERN Symposium, 1956 (no abs t r ac t ) .
R. B. Neal, "Design of Linear Electron Accelerators with Beam Load-
ing," M. L. Report No. 379, March 1957 (abs t r ac t on page 74).
R. B. Neal, "Transient Beam Loading i n Linear Electron Accelerators,"
M. L. Report No. 388, May 1957 (no abs t r ac t ) .
R. B. Neal, "Design of Linear Electron Accelerators With Beam Load-
ing," Journal of Applied Physics, Vol. 29, No. 7, 1019-1024, July 1958 (no a b s t r a c t ) e
K. G. Dedrick, " A Theoretical Analysis of Linear Accelerators Using
Equivalent C i rcu i t s and Cavity Normal Modes," M. L. Report No. 439, March 1958 ( a b s t r a c t on page 75)-
R. Bo Neal, "Theory of the Constant Gradient Linear Electron Ac-
ce le ra tor , " M. L. Report No. 513? May 1958 (abs t r ac t on page 76).
J. Jasberg and J. V. Lebacqz, '9Problems Related t o Very High Power
Windows a t Microwave Frequencies," M. L o Report No. 519 (abs t rac t on
page 78).
J. V. Lebacqz, J. Jasberg, H. J, Shaw, and S . Sonkin, "High-Power
Windows a t Mfcrowave Frequencies," Proceedings of the I n s t i t u t i o n of
E l e c t r i c a l Engineers, Vol. 105, Part B Supplement No. 11, 1958 (abs t r ac t
on page 79). A l s o M. L. Report No. 620.
. G. A. Loew, "Non-Synchronous Beam Loading i n Linear Electron Ac-
ce le ra tors , " M. L. Report No. 740, August 1960 ( abs t r ac t on page 80) .
Issued bv Project M:
R. B. Neal, "Stanford Two-Mile Linear Electron Accelerator, I' Pro-
ceedings of the In t e rna t iona l Conference on High-Energy Accelerators
and Instrumentation, CERN, 1959 (no abs t r ac t )
- 67 -
XVII.
W.K.H. Panofsw, "The Future of High Energy Accelerators i n Physics,11
Proceedings of t he In te rna t iona l Conference on High-Energy Accelerators
and Instrumentation, CERN, 1959 (no abs t r ac t ) .
W. J. Gallagher, "Measurement Techniques f o r Periodic Structures,"
M Report No. M-205, November 1960 (no abs t r ac t ) .
D. J. Goerz, "A Molecular Sieve Trap f o r Use at lo-' Torr," October
1960, M Report No. M-219 (abs t rac t on page 81).
D. J. Goerz, " U l t r a High Vacuum Components for the Proposed Stanford
Two Mile Linear Electron Accelerator," M Report No. M-220, October 1960, ( abs t r ac t on page 82)
G. D%e, "Electron Bunching by Uniform Sections of Disk-Loaded
Waveguide.
( abs t r ac t on page 83). Par t A: General Study," M Report No. M-242-A, December 1960
M. Michael Brady, "350 Kilovolt Pulse Voltage Divider," M Report
No. M-247, January 1961 (no a b s t r a c t ) .
R. H. Helm, "Transient Beam Loading Calculations f o r Linear Electron
Accelerators e Part I: Uniform Structures; Phase Modulation," M Report
No. M-266, May 1961 ( abs t r ac t on page 84) .
B. ABSTRACTS OF TECKNICAL REPORTS AND PAEIERS
The following pages contain the Abstracts ( i f they e x i s t ) of the
Technical Reports and papers l i s t e d i n Section m 1 . A of t h i s Final Report.
- 68 -
t
Electron Orbits i n the Buncher of a Linear Accelerator
by E. A . s&rs
M. L. Report No. 252
April , 1955
ABSTFACT
The expressions f o r t he f i e l d s i n a traveling-wave l i n e a r accelera-
t o r and t h e equations of motion f o r an electron are given f o r small
radial amplitudes so t h a t t he axial motion i s independent of t h e t rans-
verse motion.
f i e l d a t t h e cathode surface f o r negl igible defocusing e f f ec t due t o the
remaining angular momentum of the electrons when leaving t h e focusing
dc magnetic f i e l d .
s t rength a t t h e input and i n the buncher on t h e focusing of t h e pa r t i c l e s
i s discussed.
t o r , and by numerical in tegra t ion of t h e equations of motion, phase-
curves and ac tua l o r b i t s are calculated f o r e ight d i f f e ren t phase en-
t rance angles.
cent of a beam in jec ted p a r a l l e l t o t h e axis and f i l l i n g t h e in jec t ion
h o l e can be accelerated t o the end of t he 220-ft acce le ra tor with EL
focusing dc magnetic f i e l d applied only t o t h e f i r s t 3 f t of t he wave-
guide.
An estimate i s made of the maximum permissible dc magnetic
The e f f ec t of t h e increasing accelerat ing f i e l d
By use of t he parameters of t he Stanford Mark I11 accelera-
From these curves it i s concluded t h a t as much as 75 per
- 69 -
I .
XVII.
Design of the Bunching Section of the Stanford Mark IV Linear Accelerator
by J. M. Ponce de Leon
M. L. Report No. 265 June, 1955
SUMMARY
During the scholastic year 1954-1955, the author had the privilege of working at the Stanford University Microwave Laboratory, assisting
in the design and construction of the 20-ft Mark IV linear electron accelerator, in anticipation of the construction of a similar machine
for the Junta de Fisica Nuclear of Spain.
The fourth in the series of this type of machine developed at
Stanford University, the new accelerator is designed for eventual use
in physical and medical research in the nominal range of 70-100 Mev.
The construction was begun with a view to providing a vehicle for the
study of the operation of linear electron accelerators themselves.
This report constitutes a contribution to this end.
A study of the bunching characteristics of the nonperiodic part of the disk-loaded structure is made by trying different combinations
of the parametric functions that determine those characteristics.
best case is chosen.
effect are introduced and the final dimensions are corrected by cold-
test microwave measurement.
The Corrections for ohmic losses and beam-loading
- 70 -
The Use of Non-Euclidean Geometry in Measurements of Periodically Loaded Transmission Lines
bY R. L. Kyhl
M. L. Report No. 282 October, 1955
SUMMARY
The propagation characteristics of periodically loaded transmission lines can be deduced from impedance measurements taken with a series of different terminating configurations in a manner analogous to the "nodal
shift" method of measuring miorwave junction characteristics.
non-Euclidean properties of impedance transformations form a particular-
ly simple approach for analyzing measurements in the case of the loaded
line.
The
- 71 -
XVII 9
Development of High-Power Modulators With Low-Voltage Components
C . B. Jones and R . B. Neal
M. L. Report No. 288
December, 1955
ABSTRACT
I n t h e work with l i n e a r e lec t ron acce lera tors a t Stanford, it has
been necessary t o develop modulators capable of producing pulses i n t h e
range of 100 megawatts and with pulse lengths from 1 t o 3 microseconds
t o provide power f o r l a rge klystron amplif iers .
are beyond the capab i l i t i e s of commercially ava i lab le switch tubes of
t h e thyratron type unless many of these tubes a r e placed i n series-
p a r a l l e l combinations which tend t o make the cos t prohibi t ive.
fo re , t h e use of switches of t he f ixed spark-gap type with provisions
f o r ex terna l t r igger ing has been found expedient.
over which the device must operate i s considerable, t he switch functions
can be accomplished by using a multi-electrode switch. A switch capable
of operating over a 9:l range i n voltage has been developed by Pearson.
This switch u t i l i z e s s i x spheres i n tandem cons t i tu t ing f i v e gaps, with
a voltage divider t o give t h e des i red voltage across each gap. A posi-
t i v e b i a s voltage of 65 kv i s put or1 the t h i r d electrode. This voltage
i s e s s e n t i a l f o r wide-range voltage operation. A t r i g g e r voltage of
about 60 kv i s applied t o the second electrode.
These requirements
There-
If t h e voltage range
This spark gap was designed t o work with a maximum charging
vol tage of 132 kv.
forming network capaci tors must be r a t ed f o r t h i s volta'ge.
transformer having a 6 : 1 step-up r a t i o i s used t o make a maximum voltage
of 396 kv ava i lab le as beam voltage f o r a high-power klystron amplifier.
The perveance of t h e klystron i s such t h a t t he peak current i n the tube
is 250 amp. The peak r-f power output from t h i s tube i s i n excess of
30 Mw.
Thus, t h e power-supply components and the pulse-
A pulse
- 72 -
Prebunching by Velocity Modulation in Linear Accelerators
bY E. A. Sm&s
M.L. Report No. 303 April, 1956
ABSTRACT
Methods of prebunching the electron beam by velocity-modulation
techniques prior to injection into a linear accelerator are discussed.
A particular method (i.e., bunching at the injection energy) is analyzed in detail for one- and two-cavity bunching.
The physical design of a single-cavity prebuncher is given for a
modulation voltage 10 percent of the injection voltage and a drift space of 40 em.
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Design of Linear Electron Accelerators with Beam Loading
by Richard B. Neal
M.L. Report No. 379 March 1937
ABSTRACT
In this report the design of linear electron accelerators under beam
loading conditions will be considered.
be confined to the traveling-wave type of accelerator of uniform modular
dimensions.
is established after the electron beam has been on steadily for a period
equal to the filling time of the accelerator structure).
For simplicity, this study will
Only the equilibrium case will be discussed (equilibrium
In general, the basic specifications of a linear accelerator are
its beam energy and average beam power.
in many ways.
be specified.
The two factors may be qualified
For example, pulse length and pulse repetition rate may
In any case these quantities must be commensurate with
the maximum duty cycle of the available r-f power source.
fall times of the pulses and their stability in time and amplitude may
also be specified.
within the scope of this report.
The rise and
These are primarily circuit problems and do not fall
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XVJI.
A Theoretical Analysis of Linear Accelerators Using Equivalent Circuits and Cavity Normal Modes
by Kent G. Dedrick
M. L. Report No. 439 March, 1958
ABSTRACT
It can be shown that a linear accelerator can be described as a
periodic inductively loaded transmission line. The inductive loading
is necessary to reduce the phase velocity of the accelerator to the
velocity of the electrons being accelerated, that is; the phase velocity
of light.
In this report, the beam hole region of the accelerator is treated
as the transmission line and the remainder of the structure as reactive
loading.
expanding the fields in these regions in terms of Slater's cavity modes.
The equivalent circuit method is of' use in analyzing the effect of coup-
ling between cavities and of other gross effects.
pansion is useful in obtaining more detailed information on the proper-
ties of an accelerator.
linear accelerator structure is given to within 30 per cent by consider- ing the contribution due to only one cavity mode, viz; the lowesl, fre-
quency mode. This is a result from the operating frequency bPing very
near the frequency eigenvalue of this lowest mode. The overali loading
must be inductive, but if there is In addition a great; deal of capacity as well, considerably more energy must be stored in the acceleraior
than is needed fop purely inductive loading. In the presently used structure, the presence of considerable capacity is betrayed in the
fact that the operating frequency is indeed very close to the lowest eigenvalue. Thus, one of the problems in designing more efficient
accelerators is that of designing a more nearly perfect inductance at microwave frequencies.
The loading is treated as equivalent circuits and also by
The cavity mode ex-
In fact, the group velocity of the Stanford
The calculations have been carried through assuming no losses,
either through beam loading or resistive wall loss.
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X V I I .
Theory of t he Constant Gradient Linear Electron Accelerator
by R . B. Neal
M. L. Report Bo. 513 May, 1958
ABSTRACT
The l i n e a r e lec t ron accelerator with t h e usual uniform modular
dimensions has t h e property t h a t t h e f r ac t iona l d i s s ipa t ive loss i n r-f
power per u n i t length i n the conducting w a l l s o f t he s t ruc tu re i s con-
s t a n t over t h e e n t i r e length.
power and t h e e l e c t r i c f i e l d s t rength i n t h e s t ruc tu re decrease expo-
nen t i a l ly wi th length. Thus, t he peak f i e l d i s higher than the average
f i e l d i n t h e s t ruc ture . I n an acce lera tor of optimum design, it may be
shown t h a t t h e r a t i o of peak t o average f i e l d s i s approximately 1.75 (negl ig ib le beam loading case) .
This means t h a t t h e magnitude of the r-f
The m a x i m u m e lec t ron energy which may be achieved i n a given
length i s l imi t ed by t h e peak f i e l d s which may be produced i n the
acce lera tor s t ruc tu re without arcing, excessive f i e l d emission, or
gassing. It i s c l e a r t h a t a s t ruc tu re designed t o have a constant
f i e l d throughout can produce e lec t ron energies about 1.75 t i m e s a s high
as an optimized uniform s t ruc tu re when both are operating a t the l i m i t
o f e l e c t r i c f i e l d strength. O f course, a l a rge r amount of r-f power i s
needed t o obtain t h e increased electron energies but even with the same
power input t h e constant gradient s t ruc tu re produces s l i g h t l y higher
e lec t ron energies than the uniform s t ruc ture . The increased acceiera-
t i o n i s not large enough t o warrant t he more complicated d-esign of the
constant gradient s t ruc ture . Such a design i s indicated however where
the e l e c t r i c f i e l d s expected i n t h e s t ruc tu re a r e near t h e c r i t i c a l
value a t t h e operating frequency.
The cons tan t gradient l i nea r e l e c t r o n accelerator has previously
been s tudied under t h e simplifying assumption of zero beam loading. I n
t h i s repor t , t h e e f f e c t of beam loading upon t h e design and performnce
of t he acce lera tor will be examined. I n addi t ion , t h e r e s u l t s w i l l be
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given i n dimensionless form s o t h a t t h e various equations and graphs can
'be used a t any operating frequency.
Another advantage of' t h e constant gradient accelerator which w i l l
be shown i n t h i s study i s t h a t it i s somewhat less subject t o beam
loading than t h e uniform accelerator s t ruc tu re . Thus, f o r an accelera-
t o r of given f i l l i n g time and length, it should be possible t o obtain
approximte ly 5 t o 20 per cent more beam power with t h e constant gradient
machine.
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I
Problems Related t o Very High Power Windows a t Microwave Frequencies
by J. Jasberg and J. V. Lebacqz
ML>L. Report No. 519 March, 1958
ABSTRACT
A discussion i s given of the types of windows used on the 20 MW
klystrons which serve as sources of radiofrequency power f o r the high-
energy l i n e a r e lec t ron accelerator a t Stanford University. Both cera-
mic d isk windows and ceramic cone windows have been used f o r t h i s purpose,
and several methods of mounting the window i n the output waveguide of
the tube have been t r i e d . The choice of both physical and e l e c t r i c a l
cha rac t e r i s t i c s of the windows are d ic ta ted by considerations of s i z e ,
power l eve l , i r r a d i a t i o n by electrons and X-rays, vacuum requirements
and the l i k e . The s ingle most important requirement of these windows
i s t h a t they should have long l i f e , s ince window l i f e i s now the major
f ac to r i n l i f e of the tubes. Results a re presented on average l i f e of
the windows over the period of the l as t few years. The causes of
f a i l u r e are not completely understood a t the present t i m e , but a d i s -
cussion i s given of the typ ica l kinds of f a i l u r e and the fac tors which
influence window l i f e . The goal of window research a t Stanford i s t o
increase the r e l i a b l e operation l i f e of windows from the present value
of approximately 1900 hours t o perhaps 5000 hours.
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High-Power Windows at Microwave Frequencies
by J. V. Lebacqz, J. Jasberg, H. J. Shaw, and S. Sonkin
M.L. Report No. 620 March, 1958
SUMMARY
During the past ten years the Microwave Laboratory at Stanford
University has been engaged in development work on high-power klystrons.
One of these is used in the linear accelerator and is operated at 20 MW
(peak) and a few kilowatts average.
operate between 1 and 3 MW (peak) in the X-, S- and L-bands. teristics of the output windows of these tubes are briefly reviewed, and
the information obtained on life and the mechanism of failure of the windows used for the linear-accelerator klystron is considered in detail.
The others, now produced commercially,
The charac-
From the operation of approximately 120 windows used with the ac- celerator tubes, an average window life of nearly 2000 hours has been
observed. Most of the windows used with the accelerator consist of a
ceraxic disc in a circular waveguide.
a series of small holes in the ceramic, one of which eventually punctures the disc.
tion of the E-field in the guide. The reasons for these failures are
not yet clearly understood,
are continuing on the effects of the impurities of the material, particle
bombardment, X-ray bombardment, and geometry of the window. We expect,
when a better understanding of the mechanism of failure has been achieved,
that the average window life can be increased to a minimum of 5000 hours.
Most failures appear to start as
The general direction of the puncture is normal to the direc-
Experimental and theoretical investigations
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X E I .
Non-Synchronous Beam Loading in Linear Electron Accelerators
bY G. A. L o w
M. L. Report No. 740 August 1960
ABSTRACT
The purpose of this report is to discuss the steady-state behavior
of the electrons in a linear accelerator where the rf wave is not in
perfect synchronism with the beam.
The problem of beam loading in linear electron accelerators has been examined by a number of authors.
mum case where the electrons start on the crest of the wave and remain
in synchronism with it along the accelerator. More recently, the prob-
lem of imperfect initial phasing has been investigated where the elec-
trons do not ride the crest of the wave. Some attention has also been
given to the case where the rf phase velocity and the electron velocity
are not exactly equal.
state beam-loading theory which simultaneously takes into account the
effects of imperfect initial phasing and non-synchronism. By non- synchronism is meant that the rf phase velocity differs slightly from
the velocity of the electrons, which is taken to be e, the velocity of
light. Some practical observations are drawn from this study concerning
initial phasing, excitation by the beam, and the energy reduction due to
beam loading.
Early studies considered the opti-
This report presents an extension of the steady-
- 80 -
A Molecular Sieve Trap fo r U s e a t lo-’ Torr
bY David J. Goerz Jr-
M Report No. 219
October, 1960
ABSTRACT
A molecular s ieve t r a p can 5e made which w i l l operate i n range of
t o lo-’ Torr over a period of several months without processing. -8 10
It i s easy and e.conomica1 t o use with an i n t e r n a l heater and se l f -
contained water ba f f l e .
- 81 -
. . 1
mr I.
Ultra High Vacuum Components f o r the Proposed Stanford Two Mile Linear Electron Accelerator
by David J. Goerz Jr.
M Report No. 220
October, 1960
ABSTFACT
A number of a l l metal components have been developed a t Stanford
University f o r the proposed two mile l i n e a r e lec t ron accelerator .
include a vacuum s e a l f o r waveguide, a one inch bakeable u l t r a high
vacuum valve and an a l l metal bakeable waveguide valve, su i tab le f o r
highpower S-band (10 em) radiofrequency transmission. A l l components
have a leak r a t e l e s s than 10-l' standard cc/sec. of Helium.
These
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1
Electron Bunching by Uniform Sections of Disk-Loaded Waveguide Part A: General Study
by Georges Dame
M.L. Report No. 780-~ M Report No. 242-A December, 1960
S W A R Y
Rather than dealing with nonperiodic disk-loaded structures, an
exhaustive study is made of the properties of a uniform waveguide sec-
tion, i.e., a section where the electric-field strength and the phase
velocity of the traveling wave are constant along the axis.
appears that if the phase velocity of the wave in a waveguide section
is equal to the injection velocity of the unmodulated electrons, this waveguide section can f’unction effectively as a prebuncheS and would
not require more than a hundred of watts of rf power for this purpose.
This type of buncher is compared with a velocity-modulating
It
cavity followed by a drift space. It is shown that it can achieve better bunching than is obtained by velocity modulatiw, and is also
less sensitive to small fluctuations of the rf power level.
- 83 -
XVII .
Transient Beam Loading Calculations for Linear Electron Accelerators Part I: Uniform Structures; Phase Modulation
by R. H. Helm
M Report No. 266 May, 1961.
ABSTRACT
This report contains a summary of results on calculations of the
transient beam loading in axially uniform linear electron accelerators.
The effects’of transient phase modulations in the rf field and in the
bean current are includedo Formulae and numerical results are given for several special examples.
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1