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FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tilt studies at FLASH
FEL studies – Autumn 2007People involved: Kirsten Hacker, Christopher Gerth, Eduard PratFEL Beam Dynamics Meeting19th of November of 2007, Hamburg
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Contents
• Overview of the measurements• Orbit response measurements• Beam tilt
– Measurements and simulations of beam tilt and emittance– Measured and simulated dispersion
• C-shape– Simulation of a possible source– Measurements
• Summary and next steps
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Overview of the measurements
y
x
2007-10-29T125554-C-SHAPE-MIRIS-ORBITbadcshape.mat
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10
20
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60y
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2007-10-28T120852-V2GUN-TILT-SCAN.mat
240 260 280 300 320 340 360 380 400 420
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BEAM TILT MEASUREMENTS (23-10-07 & 28-10-07)A vertical offset through ACC1 (running off-crest) tilts the beam at BC2 and generates an emittance increase.Using the gun steerers, we generated different vertical bumps at BPM9ACC1. For each bump we measured:-Dispersion from ACC1-Beam tilt at BC2 using SR camera-Emittance at DBC2 using 4 OTR stations at DBC2
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2007-10-28T105912-V2GUN-TILT-SCAN.mat
280 300 320 340 360 380 400 420
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C-SHAPE MEASUREMENTS (28-10-07 & 29-10-07)Running ACC1 on-crest, beam at BC2 can have a C-shape (for some optics and gun phase)We have analyzed the C-shape for different iris & mirror positions and as a function of the orbit
Complementary measurements- Orbit response for gun steerers (23 & 28-10-07)- Beam energy and energy spread after the gun (29-10-07)
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Orbit response measurements23-10-07
0 2 4 6 8 10 12-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1V1GUN (23-10-07)
#BPM
Orb
it re
spon
se [m
m/m
rad]
1mradmodel
0 2 4 6 8 10 12-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4V3GUN (23-10-07)
#BPM
Orb
it re
spon
se [m
m/m
rad]
1mradmodel
0 2 4 6 8 10 12-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8V2GUN (23-10-07)
#BPM
Orb
it re
spon
se [m
m/m
rad]
1mradmodel
Wrong calibration sign of BPM9ACC1 (changed)Wrong calibration constant of BPM1/2UBC2 (changed)Wrong polarity of V3GUN (changed)
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Orbit response measurements28-10-07
0 2 4 6 8 10 12-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1V2GUN (28-10-07)
#BPM
Orb
it re
spon
se [m
m/m
rad]
0.5mrad0.5mrad1mrad1mradmodel
0 2 4 6 8 10 12-8
-6
-4
-2
0
2
4
6V10ACC1 (28-10-07)
#BPM
Orb
it re
spon
se [m
m/m
rad]
1mrad0.1mrad
After the changes ~ good agreement ☺ ✔
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tilt measurements – 28-10-2007Beam tilt
y
x
2007-10-28T105016-V2GUN-TILT-SCAN.mat
280 300 320 340 360 380 400 420 440
34
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Beam tilt for no bump is not zero(For no bump, orbit at BM9ACC1 was -2.8mm)
-6 -4 -2 0 2 4 6 8-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
Bump amplitude at BPM9ACC1 [mm]
Bum
p de
pend
ent t
ilt a
t D3B
C2
[deg
]
SR Camera BC2: Bunch tilt measurement 28-Oct-2007
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tilt measurements – 28-10-2007Emittance at DBC2 (90% values)
-4 -3 -2 -1 0 1 2 3 4 51
1.5
2
2.5
3
3.5
4
4.5
bump amplitude at BPM9ACC1 [mm]
emitt
ance
mea
sure
d at
DB
C2
[um
]
90% horizontal emittance90% vertical emittancehorizontal mismatchvertical mismatch
ACC1 9 degrees off crest
Emittance is not minimum for no bump(For no bump, orbit at BM9ACC1 was -2.8mm)
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tilt simulations
Steerer currents of the measurements for V1/2/3GUN (& bump artificially closed)
Parameters of initial distribution:Emittance=1.3μmMomentum chirp = -4%Bunch Length=1.7mm,Energy spread = 0.4%
0 5 10-5
0
5
0 5 10-5
0
5
0 5 10-10
0
10
0 5 10-5
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5
0 5 10-5
0
5
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10
0 5 10-10
0
10
simulationmeasurement
Simulated vs measured orbit difference [mm]
105 particlesWakes included (structure and coupler)0.62nC9 degrees off crest at ACC1Optics of the measurements
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tilt simulationsBasic case (zero bump = zero orbit, no wakes)
-6 -4 -2 0 2 4 6-2
-1
0
1
2
bump at BPM9ACC1 [mm]
beam
tilt
at B
C2
[deg
rees
]
-6 -4 -2 0 2 4 60.5
1
1.5
2x 10-6
bump at BPM9ACC1 [mm]
emitt
ance
at D
BC
2 [u
m]
No bump corresponds to no tilt and to optimum emittance
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tilt simulationsReal case (no bump=-2.8mm at BPM9ACC1)
Initial orbit misalignment of 3.5mm reproduces the initial orbit at BPM9ACC1 (-2.8mm)
-8 -6 -4 -2 0 2 4-1
0
1
2
3
orbit at BPM9ACC1
beam
tilt
at B
C2
[deg
rees
]
-8 -6 -4 -2 0 2 42
2.5
3
3.5x 10-6
orbit at BPM9ACC1
emitt
ance
at D
BC
2 [u
m]
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tiltMeasurements vs simulations
Beam tilt: if some initial offset good agreementEmittance: qualitative good agreement
EmittanceBeam tilt
-6 -4 -2 0 2 4 6 81
1.5
2
2.5
3
3.5
4
bump amplitude at BPM9ACC1 [mm]
emitt
ance
mea
sure
d at
DB
C2
[um
]
measured emittancemeasured mismatchsimulated emittance
-6 -4 -2 0 2 4 6 8-1
-0.5
0
0.5
1
1.5
2
2.5
Bump amplitude at BPM9ACC1 [mm]
Bum
p de
pend
ent t
ilt a
t D3B
C2
[deg
]
measurements fitmeasurement pointssimulations
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Beam tilt: Dispersion from ACC1 Measurements and simulations
3 4 5 6 7 8 9 10-30
-20
-10
0
10
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#BPM
Dis
pers
ion
[mm
]MEASURED VERTICAL DISPERSION
-1.9mm-4.9mm+1.6mm+3.2mm+4.3mm+5.9mmref
3 4 5 6 7 8 9 10-15
-10
-5
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5
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#BPM
Dis
pers
ion
[mm
]
MEASURED HORIZONTAL DISPERSION
ref-1.9mm-4.9mm+1.6mm+3.2mm+4.3mm+5.9mmref2
3 4 5 6 7 8 9 10-30
-20
-10
0
10
20
30
#BPM
Dis
pers
ion
[mm
]
SIMULATED VERTICAL DISPERSION
ref-1.9mm-4.9mm+1.6mm+3.2mm+4.3mm+5.9mm
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Comparison between measured and simulated dispersion for each bump
0 5 10-20
0
20
#BPM
Dis
pers
ion
[mm
]meassimulation
0 5 10-50
0
50
#BPM
Dis
pers
ion
[mm
]
0 5 10-20
0
20
#BPM
Dis
pers
ion
[mm
]
0 5 10-50
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50
#BPM
Dis
pers
ion
[mm
]
0 5 10-20
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#BPM
Dis
pers
ion
[mm
]
0 5 10-50
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50
#BPM
Dis
pers
ion
[mm
]
meassimulation
Good agreement ☺
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
C-shape simulations: a possible sourceEnergy chirp coming from the gun + vertical dispersion
-3 -2 -1 0 1 2 3 4 5
x 10-3
-4
-3
-2
-1
0
1
2
3
4x 10
-3
x[m]
y[m
]
Initial kick of 20mrad compensated with V2/3GUN, E=4.5MeVenergy chirp=6%wakes included
What can generate such a kick? Solenoid misalignment?
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Simulations of the C-shapeMoving ACC1 phase
-2 -1 0 1 2 3 4 5 6 7
x 10-3
-4
-3
-2
-1
0
1
2
3
4x 10-3
x[m]
y[m
]
screen 3BC2, tita=14.2196
-2 0 2 4 6 8 10
x 10-3
-4
-3
-2
-1
0
1
2
3x 10-3
x[m]
y[m
]
screen 3BC2, tita=-19.5634
+ 2 degrees - 2 degrees
Same effect observed in measurements
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
C-shape measurements
After adjusting gun phase and optics …
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2007-10-29T121447-C-SHAPE-MIRIS-0.mat
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… C-shape is there
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Moving ACC1 phase
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2007-10-29T125631-C-SHAPE-MIRIS-ORBITbadcshape.mat
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2007-10-29T125554-C-SHAPE-MIRIS-ORBITbadcshape.mat
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2007-10-29T125613-C-SHAPE-MIRIS-ORBITbadcshape.mat
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-Same effect observed during measurements before the shutdown-Same effect predicted by simulations
-1 degree
+ 1 degree reference
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Pseudo solenoid misalignment
Moving both iris and mirror positions the beam is misaligned respect to the gun.
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Moving vertically
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2007-10-29T124226-C-SHAPE-MIRIS-up085.mat
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2007-10-29T124544-C-SHAPE-MIRIS-REF.mat
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2007-10-29T122445-C-SHAPE-MIRIS-down06.mat
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2007-10-29T122739-C-SHAPE-MIRIS-down18.mat
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↑0.85mm reference
↓0.60 mm ↓1.80 mm
C-shape does not change significantly when moving up and down
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Moving horizontally
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2007-10-29T121954-C-SHAPE-MIRIS-right2.mat
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2007-10-29T110620-C-SHAPE-MIRIS-right0875.mat
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2007-10-29T115727-C-SHAPE-MIRIS-000.mat
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2007-10-29T120004-C-SHAPE-MIRIS-left083.mat
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Movement to the right enhances C-shapeMovement to the left reduces the effect
→2.00mm →0.88mm
reference ←0.83mm
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Orbit correction
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x
2007-10-29T121954-C-SHAPE-MIRIS-right2.mat
10 20 30 40 50 60
10
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x
2007-10-29T125554-C-SHAPE-MIRIS-ORBITbadcshape.mat
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x
2007-10-29T120004-C-SHAPE-MIRIS-left083.mat
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→2.00mm
←0.83mm
Orbit as →2.00mm
Correcting the orbit without moving iris and mirror has a similar impact to the C-shape as moving iris and mirror
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2007-10-29T125001-C-SHAPE-MIRIS-ORBITnocshape.mat
10 20 30 40 50 60
10
20
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Orbit as ←0.83mm
FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY
Summary and next steps
SummaryGood agreement between model and measured orbit response for gun steerersBeam tilt:
Measurements of beam tilt, emittance and dispersion are in a good agreement with simulations. Initial conditions (without gun steering) were not optimal.
C-shape:Correcting the orbit has a similar effect as moving iris and mirror positions.Vertical dispersion created upstream ACC1 would generate the C-shape (simulated and ~ confirmed by measurements)
Next stepsAnalyze beam energy measurementDo more precise simulations (using initial distribution from ASTRA, using same way to determine beam tilt for measurements and simulations, etc.)
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