p. emma, slacicfa xfel 2004 - july 29, 2004 electron bunch measurements with a transverse rf...
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P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Electron Bunch Measurements Electron Bunch Measurements with a Transverse RF Deflectorwith a Transverse RF Deflector
P. EmmaP. Emma ICFA XFEL 2004 WorkshopICFA XFEL 2004 Workshop
July 29, 2004July 29, 2004
ICFA Future Light Sources Sub-panel ICFA Future Light Sources Sub-panel Mini-workshop on XFEL Short Bunch Measurement and Timing Mini-workshop on XFEL Short Bunch Measurement and Timing
Stanford Linear Accelerator CenterStanford Linear Accelerator Center, July 26 - 30, 2004, July 26 - 30, 2004
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Previous Talks/PublicationsPrevious Talks/Publications
R. Miller, IEEE Trans. Nucl. Sci., June 1965.R. Miller, IEEE Trans. Nucl. Sci., June 1965.
X.-J. Wang, PAC’99, March 1999.X.-J. Wang, PAC’99, March 1999.
J. Frisch, BNL/LCLS Diag. Workshop, March 2000.J. Frisch, BNL/LCLS Diag. Workshop, March 2000.
P. Emma et al., LCLS-TN-00-12, Aug. 2000.P. Emma et al., LCLS-TN-00-12, Aug. 2000.
R. Akre et al., PAC’01, June 2001.R. Akre et al., PAC’01, June 2001.
R. Akre et al., EPAC’02, June 2002.R. Akre et al., EPAC’02, June 2002.
H. Schlarb: H. Schlarb: http://www.desy.de/s2e/ (Aug. 2003).
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Transverse RF Deflector in the SLAC LinacTransverse RF Deflector in the SLAC Linac
VV00 20 MV 20 MVzz 50 50 m, m, EE 28 GeV 28 GeV
ee
zz
2.44 m2.44 m
cc pp
90°90°
VV((tt))yy
RFRF‘‘streak’streak’
SS-band-band
RF InputCoupler
BeamDeflection
Irises withmode-lockingholes
RF InputCoupler
BeamDeflection
Irises withmode-lockingholes
built in 1960’s built in 1960’s (G. Loew…)(G. Loew…)
built in 1960’s built in 1960’s (G. Loew…)(G. Loew…)
ffrfrf = 2856 MHz = 2856 MHz
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Short Bunch Generation in the Short Bunch Generation in the SLACSLAC Linac Linac
1-GeV Damping Ring1-GeV Damping Ring
z z 1.1 mm1.1 mm zz 50 50 mm zz 12 12 mm
zz 6 mm 6 mmSLAC LinacSLAC Linac
30 GeV30 GeV
FFTBFFTB
Existing bends compress to 80 fsecExisting bends compress to 80 fsec
1.5 Å1.5 Å
compression by factor of compression by factor of 500500
1.5%1.5%
28.5 GeV28.5 GeV
80 fs 80 fs FWHMFWHM
30 kA30 kA
RF DeflectorRF Deflector
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Linac InstallationLinac Installation
SPPSSPPS::LL = 2.4 m = 2.4 mff = 2856 MHz = 2856 MHz
TTF-2TTF-2::LL = 3.6 m = 3.6 mff = 2856 MHz = 2856 MHz
LCLSLCLS::L L = 0.5 & 2.4 m= 0.5 & 2.4 mff = 2856 MHz = 2856 MHz
P. KrejcikP. Krejcik
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
MeasurementsMeasurements
RF Deflector RF Deflector OFFOFF
RF Deflector RF Deflector ONON
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
3-Point Bunch Length Measurement3-Point Bunch Length Measurement
Asymmetric parabola indicates Asymmetric parabola indicates incoming beamincoming beam tilttilt
Bunch length Bunch length reconstruction:reconstruction:
measure streak at 3 measure streak at 3 different RF phasesdifferent RF phases
Y = A * (X - B)**2 + CA = 1.6696E-02 STD DEV = 1.3536E-03B = 28.23 STD DEV = 3.084C = 1328. STD DEV = 8.235RMS FIT ERROR = 23.63
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
****
***
**
**
*
****
********
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
E
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
-80 -40 0 40 80
SBST LI29 1 PDES (S-29-1)
1.7
1.6
1.5
1.4
1.3
X103
E
MANUAL STEPPING. STEPS = 30
1-APR-03 20:21:16
Cavity on+180°
Cavity off
Cavity on180°
zz = 90 = 90 mm
yy22
RF deflector phase (deg)RF deflector phase (deg)
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Practical IssuesPractical Issues
Extracting rms beam size from non-Gaussian, Extracting rms beam size from non-Gaussian, noisy screen imagenoisy screen image
Screen calibrationScreen calibration
Limited field of view on screenLimited field of view on screen
RF phase drift during measurementRF phase drift during measurement
Inadequate RF voltageInadequate RF voltage
Clumsy softwareClumsy software
Data acquisition time vs. beam drift timeData acquisition time vs. beam drift time
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Voltage/Screen CalibrationVoltage/Screen CalibrationB
PM
B
PM
yy-p
ositi
on a
fter
def
lect
or (
mm
)-p
ositi
on a
fter
def
lect
or (
mm
)
RF deflector phase (deg)RF deflector phase (deg)
BPM calibration is only BPM calibration is only accurate to ~10% level: accurate to ~10% level:
……better to calibrate better to calibrate amplitude on screen and amplitude on screen and get pixels/deg (P. Krejcik)get pixels/deg (P. Krejcik)
RF phase setting is RF phase setting is highly accuratehighly accurate
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Screen Pixel Calibration ErrorsScreen Pixel Calibration Errors
Errors on Errors on xx-axis produce bias in standard linear regression techniques…-axis produce bias in standard linear regression techniques…
T. Lohse, P. Emma, SLAC-CN-371, Feb 1989.T. Lohse, P. Emma, SLAC-CN-371, Feb 1989.
nono noise on noise on xx-axis:-axis:slopeslope = = 3.5 exactly3.5 exactly
SimulatedSimulated
beam
pos
ition
beam
pos
ition
RF phaseRF phase
noise on x-axis:fitted-slope = 2.6 (true = 3.5)
SimulatedSimulated
beam
pos
ition
beam
pos
ition
RF phaseRF phase
(from H. Schlarb’s 2003 talk)(from H. Schlarb’s 2003 talk)
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Screen Pixel CalibrationScreen Pixel Calibration(from H. Schlarb’s 2003 talk)(from H. Schlarb’s 2003 talk)
100% klys. drive:100% klys. drive:0.427 mm/deg0.427 mm/deg
50% klys. drive:50% klys. drive:0.0415 mm/deg0.0415 mm/deg
50% klys. drive:50% klys. drive:4.92 pix/deg4.92 pix/deg
less sensitive to timing jitterless sensitive to timing jitter
scre
en
scre
en yy
-pos
ition
(pi
x)-p
ositi
on (
pix)
BP
M
BP
M yy
-pos
ition
(m
m)
-pos
ition
(m
m)
BP
M
BP
M yy
-pos
ition
(m
m)
-pos
ition
(m
m)
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
RF Deflector as Arrival Time MonitorRF Deflector as Arrival Time Monitor
At 14 GeV, a 10-At 14 GeV, a 10-m BPM resolution can m BPM resolution can resolve resolve <10 fsec<10 fsec timing error – but must timing error – but must also consider RF phase jitter.also consider RF phase jitter.
EE00 28 GeV, 28 GeV, VV00 24 MV, 24 MV, yy 50 m 50 m
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Location of Main Linac DiagnosticsLocation of Main Linac Diagnostics
5+ energy spread meas. stations (optimized with small )5+ energy spread meas. stations (optimized with small )
...existing linac...existing linac
L0L0
rfrfgungun
L3L3L1L1 XX L2L2
xx,,yy xx,,yy xx,,yy xx,,yy
xx,,yy
EE EE EEEE
5+ emittance meas. stations designed into optics (x,y)
slice measurements possible with transverse RF (L0 & L3)BPMs at or near most quadrupoles and in each bend syst.
RF deflectors for slice and E measurements
EE
EE EEEEEE EE
T-cav.T-cav.
T-cav.T-cav.
xx,,yy??
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Slice-Emittance Measurement SimulationSlice-Emittance Measurement SimulationRF-deflector at 1 MVRF-deflector at 1 MV
slice OTR 10 timesslice OTR 10 times
yy bunch length bunch length
scannedscanned quadquad
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Slice-Emittance Measurement SimulationSlice-Emittance Measurement Simulation
slice-5slice-5
Injector at 135 MeV with Injector at 135 MeV with S-band RF-deflector at 1 MVS-band RF-deflector at 1 MV = meas. sim.
= calc.= y distribution= actual
(same SLAC slice-(same SLAC slice- code used at BNL/SDL) code used at BNL/SDL)
(slice-y-emittance also simulated in BC1-center)
P. Emma, P. Emma, SLACSLAC ICFA XFEL 2004 - July 29, 2004ICFA XFEL 2004 - July 29, 2004
Slice Energy Spread Measurements in LTUSlice Energy Spread Measurements in LTU
LTU at 14 GeV with S-band LTU at 14 GeV with S-band RF-deflector at 24 MVRF-deflector at 24 MV
FEL goalFEL goal
EE//E E 104
x 12 m