new type of a bunch compressor and generation of a short wave length coherent radiation
DESCRIPTION
New type of a bunch compressor and generation of a short wave length coherent radiation. A. Zholents (ANL) and M. Zolotorev (LBNL). LBNL, August 06, 2010. “Any fool with four dipoles can compress a bunch” - anonymous. OK, but there may be a few details to consider…. - PowerPoint PPT PresentationTRANSCRIPT
New type of a bunch compressor and generation of a short wave length coherent radiationA. Zholents (ANL) and M. Zolotorev (LBNL)
LBNL, August 06, 2010
LBNL, 08-06-2010
“Any fool with four dipoles can compress a bunch”
- anonymous
OK, but there may be a few details to consider…
P. Emma, ICFA Workshop, Sardinia, 2002
LBNL, 08-06-2010
sz0
DE/E
z
sz
under-compression
V = V0sin(wt)
RF AcceleratingVoltage
Dz = R56DE/E
Path Length-EnergyDependent Beamline
DE/E
z
sE/E
DE/E
z
‘chirp’
Courtesy P. Emma
RF Chicane
Magnetic Bunch Compression
LBNL, 08-06-2010
Some issuesDE/E
zsz
under-compression
Needs:de-chirping
De-chirping istypically done by using wake fields and/or off-crest acceleration
DE/E
zsz
under-compression
Full compression
Full compression is not good because of emittance growth due to CSR
LCLS
K. Bane et al., PRST AB, 12, 030704 (2009)
LBNL, 08-06-2010
References
P. Emma, Z. Huang, K.-J. Kim, P. Piot, “Transverse-to-Longitudinal Emittance Exchange to Improve Performance of High-Gain Free-Electron Lasers”, Phys. Rev. ST Accel. Beams 9, 100702 (2006).
M. Cornacchia, P. Emma, “Transverse to longitudinal emittance exchange”, Phys. Rev. ST Accel. Beams 5, 084001 (2002)
R.P. Fliller, D.A. Edwards, H.T. Edwards, T. Koeth, K.T. Harkay, K.-J. Kim, “Transverse to longitudinal emittance exchange beamline at the A0 Photoinjector”, Part. Acc. Conf., PAC07, (2007).
Results presented here use the idea of transverse to longitudinal emittance exchange
LBNL, 08-06-2010
A schematic of the bunch compressor
BQD
QF BQD
QF B
QDQF
B B
B
QDQF
QF QFQD QD QD QF
QFQD
M+ M+D+ M- M-D-T
B
B
Variant 1
TM110 TM010TM010
Deflecting cavity
BQD
QF BQD
QF B
QDQF
B B
B
QDQF
QF QFQD QD QD QF
QFQD
I T
B
B
I I I
Focusing properties of individual sections
z →x emit. exch. x → z emit. exch.Telescope
(manipulate longitudinal phase space with ease of a transverse phase space)
LBNL, 08-06-2010
A schematic of the bunch compressor: alternative variant
QF QFQD QD QF
BQD
QF BQD
QFQD
M+ M+D+
M+ M+D+ T
BQD
QF BQD
QFQD
B
B
BVariant 2
B
TM110 TM010TM010
Deflecting cavity
LBNL, 08-06-2010
xkxEaeV
taxJEeV
rf 01
0 )cos()/(2
w
zkctEaeV
taxaxJ
EeV
x rf D 010 )sin(/
)/(2w
B B
Deflecting cavity
Courtesy: Li, Corlett
Thin cavity approximation:
In agreement withPanofsky-Wentzeltheorem
LBNL, 08-06-2010
TM110
TM110 TM010TM010
zxx
dkkdk
kkdd
16/2/010001002/1
12
1
11
d1
One can cancel unwanted energy gain using two TM010 mode side cavities
102/010001002/1
kdk
kkdd
2011
12
EeV
ad
EeV
Required energy gain in each TM010 cavity
Thick deflecting cavity:
d
LBNL, 08-06-2010
FNAL: SRF five cell prototypeEbeam = 250 MeVfRF = 3.9 GHzV0 = 4 MV (1m, 3x7 cells: Li, Corlett)V1 = 0.4 MVk = 0.013 cm-1
SLAC: copper X-band LOLAEbeam = 250 MeVfRF = 11.4 GHzV0 = 22 MV ( 0.5 m)V1 = 6.6 MVk = 0.21 cm-1
LBNL, 08-06-2010
BQD
QF B
BQD
QF BQD
QFQD
B
100010
001001
L
M
E
kk
kkMDM
00000
00000
The following constrains were used:
12/
kdL
56R
First leg of emittance exchange scheme
Complete emittance exchange scheme
zpx
x
LBNL, 08-06-2010
QF QFQD QD QFQD
T
1000010000/10000
mm
T
Telescope
Total transformation
m
mmm
kETE
000
)1(100
0010001
2
BQD
QF BQD
QF B
QDQF
B B
B
QDQF
QF QFQD QD QD QF
QFQD
I T
B
B
I I I
z →x emit. exch. x → z emit. exch.Telescope
LBNL, 08-06-2010
222
22222
)1()1(1
iif
iif
z
zz
hm
mm
mm
hm
sss
sss
Bunch length and energy spread at the end of the schemeDefine: - bunch length before compression, - uncorrelated relative energy spread before compression, and - energy chirp before compression
izs
dzEdh /)(lni
s
- bunch length after compression, - uncorrelated relative energy spread after compression
fzs
fs
Using entire mapping one obtains :
LBNL, 08-06-2010
mif zz /ss
No chirp case, e.g., h = 0
if
i
i
f
m
mmm
zz
ss
ss
s
2222
2
)1(
Case 1
mm
mi
i
zss )1( then
Case 2
mm
mi
i
zss )1( Then the compression is not yet finished
LBNL, 08-06-2010
The last element of proposed BC is the chicane/dogleg with its R56 used to cancel the R56 accumulated upstream
)/11( 256 mR
mm
k
000
0100
0010001
2
if
if
mm zz
ss
ss
1
Then, the entire mapping takes the following form:
… and we obtain for the final bunch length and relative energy spread:
LBNL, 08-06-2010
… or one may prefer to wait until the electron beam gains energy from E1 to E2 and do the final compression at E2
Then R56 for the final step should be:
1
2256 )/11(
EEmR
2
1
1
EEm
m
if
if zz
ss
ss
… and we obtain for the final bunch length and relative energy spread:
Possible advantage of a Deferred Compression is reduction of the gain of the microbunching instability and impact of other collective forces:
a) electron bunch is not yet compressed to the shortest sizeb) energy spread has already grown up to the final value
LBNL, 08-06-2010
Because there is no need in energy chirp for compression: a) one can use BC even after the linac and obtain final
compression in a “spreader”/ “dogleg” part of the lattice leading to FEL
BCGun L1 L2 Spreader
)/11( 256 mR
Possible advantages
b) or use two BCs, one in usual location and one after the linac
BC
Possible advantages (2)
Accelerate a relatively long bunch in the re-circulating linac without a chirp and compress it in the final arc.
New type of a bunch compressor
Possible cost saving
FEL
LBNL, 08-06-2010
Jitter studies
No adverse jitter effects are found:Timing jitter is compressed by a compression factor and energy jitter is increased by a compression factor:
mEEmttDD
DD /
LBNL, 08-06-2010
In the following numerical example we use: fRF = 2.85 GHz k=0.05 cm-1
cavity length = 1 m
At Eb = 250 MeV this corresponds to:V0 = 21 MVV1 = -8.7 MV
Illustration
LBNL, 08-06-2010
Lattice functions for a bunch compressor with a telescopic factor m=15.Note, matching of the vertical beta-function was not pursued.
Illustration: compression by a factor of 15-I -I -I -IT
tcav tcav B2B2B1B2B2B1
Magnets:jB1= 0.10jB2= 0.0445Length=0.3 m
bx=56 mbx=0.25 m
LBNL, 08-06-2010
BQD
QF BQD
QF B
QDQF
B B
B
QDQF
QF QFQD QD QD QF
QFQD
B
B
1
2 34 5
6 7
8
Numerical values of beam sizes at key locations
m=15
Eb=250 MeVex=0.5 mms0=10-4
sE0=25 keVsz0= 160 mm
Deferred compression 42 mm -> 10 mm
Input parameters
LBNL, 08-06-2010
Eb=100 MeVex=0.5 mms0=5x10-5
sE0=5 keVsz0= 160 mm
m=15
Same as before, but with a reduced beam energy to 100 MeVThis may eliminate a need in the laser heater
LBNL, 08-06-2010
Compression of the laser induced energy modulation for microbunching at a shorter wave length
Laser e-beam interaction
BC
Plots of longitudinal phase space at various locations
z/l
DE/s
E
Initial modulation
DE/s
E
DE/s
E
z/l
z/l
Compression factor, m=20
Compressed modulation
Bunching efficiency at m-th harmonic of modulating frequency:
laser
HGHG:EEHG:
This method: 0
3/1
21 2
mbE
mb
eb
m
Em
Em
m
E
D
D
s
s
LBNL, 08-06-2010
Compression of the laser induced energy modulation can also be made at the end of the linac
z/l
DE/s
E
Laser e-beam interaction
BCLinac
Laser e-beam interaction
BCLinac
Spreader
… or be deferred to a “spreader”/“dogleg”
LBNL, 08-06-2010
Compression of the Echo induced microbunching
BC
z/l
DE/s
E
z/l
Compression factor, m=5
LBNL, 08-06-2010
0.2
Compression of the Echo induced microbunching (2)
Peak current after compression, kA
z/l
z/l
zoom on one peak1
0.8
0.6
0.4
LBNL, 08-06-2010
BCGun L1 L2
SpreaderBCtraditional BC new type BC, m=10
Echo:harmonic number = 20
Producing 1 nm seeding beginning from 200 nm laser modulation
Ipeak=100 A Ipeak=1 kA
Total harmonic number = 20x10 = 200 !
Echo
LBNL, 08-06-2010
Other uses
BQD
QF BQD
QF B
QDQF
B B
B
QDQF
QF QFQD QD QDQF
QFQD
B
B
z →x emit. exch. x → z emit. exch.FODO
collimator
It is often desirable to get rid off the tails in longitudinal distribution and proposed scheme can be used as efficient tail cutter
SLAC, 06-29-2010
Other uses (2)
BQD
QF BQD
QF B
QDQF
B B
B
QDQF
QF QFQD QD QDQF
QFQD
B
B
z →x emit. exch. x → z emit. exch.Telescope
Collimator with slits
It is possible to create a sequence of a tightly spaced microbunches using a sequence of slits
Using demagnification of the beam size before slits and magnification after the slits can help to obtain a real tight spacing of microbunches
LBNL, 08-06-2010
Other uses (3)
BQD
QF BQD
QF B
QDQF
B B
B
QDQF
QF QFQD QD QDQF
QFQD
B
B
z →x emit. exch. x → z emit. exch.Telescope
x- px tomography here
Longitudinal phase space tomography
is - z tomography there
LBNL, 08-06-2010
Summary
1. Efficient electron bunch manipulation in the longitudinal phase space can be accomplished by first exchanging longitudinal and transverse emittances, manipulating electrons in the transverse phase space and finally exchanging emittances back to their original state.
2. One application is bunch compressor that does not need energy chirp• This can also be used for a compression of any features
introduced to the electron bunch, like, for example energy modulation produced in interaction with the laser.
3. Proposed techniques for a bunch compression allows deferred compression that might be useful to mitigate possible adverse effects caused by collective forces.