rf-gun beam based alignment at pitz/flash
DESCRIPTION
RF-Gun beam based alignment at PITZ/FLASH. M.Krasilnikov, DESY Zeuthen LCLS Injector Commissioning Workshop (ICW) October 9-11, 2006. Outline. Beam-Based Alignment ( BBA ) of RF gun: Fields and geometry BBA motivation Cathode laser BBA : PITZ FLASH Limitations of laser BBA - PowerPoint PPT PresentationTRANSCRIPT
RF-Gun beam based alignment at PITZ/FLASH
M.Krasilnikov, DESY Zeuthen
LCLS Injector Commissioning Workshop (ICW)
October 9-11, 2006
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 2
Outline
• Beam-Based Alignment (BBA) of RF gun:– Fields and geometry– BBA motivation
• Cathode laser BBA:– PITZ– FLASH– Limitations of laser BBA
• Main solenoid BBA:– Solenoid micromover system– Main problems and possible solutions– Limitations of solenoid BBA
• Conclusions
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 3
PITZ Solenoides for L=276 mm with cathode at z=0 - 16 Jun 05 - MK -
N:\4GROUPS\ZN_PITZ\SIM\KRAS\FIELDS\SOL_PITZ\SF\SOLENOID1.AM 3-09-2006 17:14:04
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RF-Gun: fields and geometry (PITZ and FLASH)
•sol.mech.axis ≠mag.axis•sol.mech.axis ≠cavity el.axis•solenoid tilt angles•fields overlapping
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 4
Solenoid tilt effect
For Ecath=25MV/m solenoid tilt angle of ~3mrad is equivalent to
1 mm transverse offset
RF-Gun Alignment Motivation
Emittance growth (@z=15m) due to RF -gun misalignment
1
1.1
1.2
1.3
1.4
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1.9
0 0.5 1 1.5 2x-offset,mm
norm
.em
it.,
mm
mra
d
-10
0
10
20
30
40
50
60
70
emit.
grow
th,
%
EmX (vs.las.offset)EmY (vs.las.offset)EmX (vs.sol.offset)EmY (vs.sol.offset)EmTr (vs.las.offset)EmTr (vs.sol.offset)
-4
-3
-2
-1
0
1
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-3 -2 -1 0 1 2 3 4 5X,mm
Y,mm
solenoidoffsetX=1mm
solenoidangleX=3mrad
Imain=0A Imain=400A
Imain=400A
5% emittance growth (lower limit estimations):laser R<800um or solenoid R<500um or solenoid angle<1.5mrad (0.086deg)
No effect in the matching section has been considered!
ASTRA Simulations of FLASH (VUV-FEL) Injector (150MeV)
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 5
Cathode Laser Alignment (FLASH)
Laser spot positioning at the photo cathode:
+Transverse displacement and angle of the laser beam can be independently changed
-•Iris position has to be adjusted for every mirror movement•No VC and e-beam simultaneously
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 6
Cathode Laser Alignment (PITZ)
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 7
BBA of Laser on Cathodez=0 z=0.276m
z=0.935m
z=0.778m
Basic measurement:Mean position of electron beam at
LOW.Screen1 (DoubleDiagCross at z=0.778m)
vs.
RF gun launch phase (SP Phase)
Conditions:•Main and bucking solenoids off•All steerers off•Dipole (even it is ~0.2m after the screen) degaussed and off•Bunch charge ~10pC, pulse train 10-50 laser pulses•Moderate RF power in the gun: 0.8-1.5MW (exclude dark current)→Pz~2.6-3.3MeV/c
Preliminay (rough) laser alignment:•Using scintillating cathode•Centering in dark current images
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 8
Beam spot at Diag.Cross
screen(z=0.78m)
“Normal” phases
“Low” phases,rf focused beam
Measurements&SimulationsSimulations
-4
-2
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-40 -20 0 20 40 60 80 100 120RF Phase,deg
Xoff (mm)
Yoff (mm)
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-40 -20 0 20 40 60 80 100 120RF Phase,deg0
0.5
1
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Me
V/c
Charge (simulated) XYrms (simulated), mm
Pmean, MeV/c
0
2
4
6
8
-40 -20 0 20 40 60 80 100 120RF Phase,deg
Be
am
ch
arg
e, p
C
Charge (measured)
Charge (simulated)
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-40 -20 0 20 40 60 80 100 120RF Phase, deg
rms
size
, mm
Xrms (measured) Yrms (measured)
Xrms (simulated) Yrms (simulated)
Beam charge, Transverse rms Size,Mean Momentum Vs. RF Phase
Beam Offset at z=0.78m Vs. RF Phase (0.5 mm vertical laser offset on the cathode has been assumed)
Measured and Simulated beam charge at z=0.78m Vs. RF Phase
Measured and Simulated beam rms size at z=0.78m Vs. RF Phase
BBA of Laser on Cathode
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 9
Cathode Laser BBA. Test Movement
yxlaser ;
Step 1: Laser test movement
One of results:(X0,Y0) – preliminary coordinates of the center at the screen
Measurement: Beam offset vs. rf phase
111 cybxa
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21 22 23 24 25 26 27 28x_screen1, mm
y_sc
ree
n1
, mm
SPPhase=121deg
SPPhase=147deg
222 cybxa Measurement: Beam offset vs. rf phase
19
20
21
22
23
24
25
21 22 23 24 25 26 27 28x_screen1, mm
y_sc
ree
n1
, mm
before
after laser test movement
SPPhase=121deg
SPPhase=147deg
1221
112
1221
112
2
2
1221
11
baba
baaV
baba
babV
a
b
baba
ba
V
VV
yxy
yxx
yx
y
x
Step 2: Laser alignment
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21 22 23 24 25 26 27 28x_screen1, mm
y_sc
ree
n1
, mm
beforeafter laser test movementafter laser alignment
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21.5
22
22.5
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20 21 22 23 24 25 26 27 28x_screen1, mm
y_sc
reen
1, m
m
before
after laser testmovement
after laseralignment
SPPhase=121deg
SPPhase=147deg
calcuated initial laser
positioncalcuated laser position
after x=-1mm
electrical axis
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 10
Cathode Laser BBA. Difficulties
•Laser intensity non-homogeneity
•Laser position jitter
•Possible damage of YAG screen homogeneity
•Earth magnetic field (x,y,z)~(0.02mT,-0.03mT,-0.009mT)
Laser position jitter
3.15
3.2
3.25
3.3
3.35
0 50 100 150 200 250 300time, sec
<X
>, m
m
1.8
1.85
1.9
1.95
2
<Y
>, m
m
X_Mean
Y_Mean
stdev<X>=13um
stdev<Y>=11um
Extreme example of a damaged screen
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 11
Main Solenoid BBA. Micromover systemmain solenoid
beam axis
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 12
Main Solenoid BBAz=0 z=0.276m
z=0.935m
z=0.778m
Basic measurement:Mean position of electron beam at
LOW.Screen1 (DoubleDiagCross at z=0.778m)
vs.
Main solenoid current
Conditions:•Bucking solenoid off•All steerers off (or consider in simulations)•Dipole (even it is ~0.2m after the screen) degaussed and off•Bunch charge ~10pC, pulse train 10-50 laser pulses – to be tuned for Imain•Moderate RF power in the gun: 0.8-1.5MW (exclude dark current )→Pz~2.6-3.3MeV/c•RF launch phase*•Laser spot size possibly small
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 13
Main Solenoid BBABeam position (<X>,<Y>) at
LOW.Scr1(z=0.778m) as a function Imain E-beam displacement with a main solenoid
sweep. Possible reasons:
•Solenoid transverse offset (Xsol,Ysol)
•Solenoid tilt angles (AngleX, AngleY)
•Laser (small) offset (Xlas,Ylas) from the center
Other factors to be considered:
•RF gun launch phase and gradient
•Small offset (from X0,Y0 obtained after laser BBA)
•Solenoid calibrationFrom the laser BBA:X0=13.0mm Y0=14.8mm
Imain=0A
Imain=320A
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 14
Main Solenoid BBA. RF-gun launch phase and gradient
(21.4MV/m;22deg)
2
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0 10 20 30 40 50 60 70F0-Gun SPPhase, deg
Pm
ean,
MeV
/c
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80
Prm
s, k
eV/c
Pzmean, MeV/c
PZrms, keV/c
Cathode laser temporal profile
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inte
nsi
ty, a
.u.
streak-camera measurement
Bunch charge (LOW.FC1) vs. gun SPPhase
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bu
nch
ch
arg
e, p
C
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<Pz>
, MeV
/c
Charge, pC
PZmean
Bunch charge (LOW.FC1) vs. gun SPPhase
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bu
nch
ch
arg
e, p
C
Integr(Prof), shif ted
Charge, pC
F0=-18deg
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 15
Simulation ToolAlignment Utility of the V-code - fast tracking code based on the
method of moments of particle distribution function
min,,,,,,,,, ** F offoffrfcathsolsolsolsollaslas YXEAngleYAngleXYXYX
,...,...,
,...,...,
320
0
22
320
0
22
YsolsolXsolsol
A
AIoff
measn
simulnynoff
measn
simulnxn
solsol
A
AIoff
measn
simulnynoff
measn
simulnxn
YXYYYwXXXw
YXYYYwXXXw
main
main
F
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 16
Main Solenoid BBA. Test movementSimultaneous simulations of beam position before
and after test movement (Xsol=0.4mm)Advantages:
•Same RF gun launch phase and gradient
•Same offset X0*,Y0*
•Same solenoid calibration
Laser_Beam_CenterX 0.20 mm
Laser_Beam_CenterY -0.26 mm
XSolMainCenter 0.85 mm
YSolMainCenter 1.12 mm
AngleXSolMain -0.0808 deg
AngleYSolMain 0.0580 deg
Ez_Field_At_Cathode 22.2 MV/m
Initial_Phase -147.2 deg
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1
2
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X, mm
Y, m
m
measured before TM
measured after TM
simulated
simulated
MainSol test movement
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 17
Main Solenoid BBA
Before BBA After BBA
Laser_Beam_CenterX 0.20 mm 0.11 mm
Laser_Beam_CenterY -0.26 mm -0.27 mm
XSolMainCenter 0.85 mm 0.041 mm
YSolMainCenter 1.12mm 0.063 mm
AngleXSolMain -0.0808 deg -0.0158 deg
AngleYSolMain 0.0580 deg 0.0057 deg
Ez_Field_At_Cathode 22.2 MV/m 22.4 MV/m
Initial_Phase -147.2deg -148.5 deg
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-101234 x, mm
y, m
m
Before BBA
After BBA
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 18
Main Solenoid BBA. Difficulties
•Laser BBA difficulties:
•Laser intensity non-homogeneity
•Laser position jitter
•Damaged YAG screen
+
•RF phase and gradient jitter
•Some uncertainty in the solenoid micromover (especially angles), z-position
Laser position jitter
3.15
3.2
3.25
3.3
3.35
0 50 100 150 200 250 300time, sec
<X
>, m
m
1.8
1.85
1.9
1.95
2
<Y
>, m
m
X_Mean
Y_Mean
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 19
RF-Gun BBA. Conclusions• BBA of Laser on Cathode:
– routine procedure at PITZ (FLASH)– based on a measurement of beam position vs. gun launch phase– test movement of the laser beam allows to determine a displacement vector
for the laser beam centering
• Main solenoid BBA:– multi-parameter task– based on beam position simulation vs. main solenoid current– test movements of the main solenoid and/or cathode laser allows to reduce
uncertainty in main solenoid misalignment
• Possible improvements:– implement earth magnetic field in BBA procedures– use BPM (LOW.BPM1) for solenoid BBA – more details on RF field profile– solenoid relative displacement online measurement
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 20
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 21
Reference RF Phase. Beam Size measurements
Transverse Beam Size at Screen 3 as a Function of RF Launch Phase for Various Main Solenoid Currents
0
2
4
6
8
10
12
14
-130 -110 -90 -70 -50 -30
SP Phase / deg
mm
Rrms(240A) / mm
Rrms(250A) / mm
Rrms(260A) / mm
Rrms(270A) / mm
Rrms(280A) / mm
Rrms(290A) / mm
Rrms(300A) / mm
Pmean (a.u)
Fmax
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 22
PITZ1 Benchmark Problem: Fields
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
-0.2 0 0.2 0.4 0.6 0.8
z, m
Bz,
T
-50
-40
-30
-20
-10
0
10
20
30
40
50
Ez,
MV
/m
Main solenoid (Imain=320A)
Bucking solenoid (Ibuck=24A)
Ez (balanced)
cathode plane
Main Solenoid Calibration
0
0.05
0.1
0.15
0.2
0.25
0.3
0 100 200 300 400 500Imain, A
|Bz_
pe
ak|
me
asu
red
, T
|Bz_peak(mT)| = 0.5871*Imain(A) + 0.3641
• Field balance in the rf gun cavity
• Solenoid calibration
• MF compensation
Ibuck=0.074847*Imain
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 23
Rough laser alignment using dark current symmetry. TTF
Dark current at TTF at screen Gun3 (z = 1.27m)
Without beam With beam
• Dark current rings originate from the edge of the Cs2Te coating and plug spring region
• A laser spot being aligned on the cathode center results in an electron beam centered with dark current rings
BBA: Step 0 – Rough Laser Alignment on the Cathode
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 24
Rough laser alignment using dark current symmetry. PITZ
Without beam With beam
Screen Diag. Cross (z = 0.87m)
Screen_PP(z = 2.62m)
BBA: Step 0 – Rough Laser Alignment on the Cathode
RF Gun Alignment: Satellites observation
@PP Screen @Dispersive Arm
@Diag.Cross, “low phase”
xy
xPz
@Diag.Cross
xy
Vacuummirror
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 26
SP phase = -130SP phase = -125SP phase = -120SP phase = -116SP phase = -114SP phase = -112SP phase = -110SP phase = -106SP phase = -100SP phase = -90SP phase = -70SP phase = -50SP phase = -30
BBA of laser on cathode
SP phase = -20SP phase = -16precision of mirror adjustment:better than 20 µm
M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 27
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mm
mra
d
EmitX(aligned)
EmitY(aligned)
EmitX (laser X-offset=1mm)
EmitY(laser X-offset=1mm)
EmitX (solenoid X-offset=1mm)
EmitY (solenoid X-offset=1mm)
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0 2 4 6 8 10 12 14 16 18z, mmm
<x> (aligned) <y> (aligned)<x> (laser X-offset=1mm) <y> (laser X-offset=1mm)<x> (solenoid X-offset=1mm) <y> (solenoid X-offset=1mm)
RF-Gun Alignment MotivationASTRA Simulations of FLASH (VUV-FEL) Injector (150MeV)
trajectory
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1.4
1.6
1.8
2
2.2
2.4
12 12.5 13 13.5 14 14.5 z, m
mm
mra
d
1
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2.5
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3.5
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4.5
5
0 1 2 3 4z, m
mm
mra
d
emittance
Emittance degradation in the matching section is not included