1. Injector Commissioning C
Injector Commissioning C. Limborg-Deprey Injector-Linac & Spectrometers Commissioning Plans Oct. 10, 2006
LCLS

2. Beam Characterization
Introduction
Beamline Layout & 2007 Baseline Parameters
Strategy
Beam Characterization
135 MeV Spectrometer
6 MeV Characterization
Longitudinal : Spectrometer
Transverse : YAGs
Risks Mitigation
Laser pulse shape
Reduced gun voltage
Solenoid alignment
Matching
Conclusion & Discussion

3. LCLS Injector Klystron Gallery Laser Room BC1 compressor DogLeg Gun
2 linacs
135 MeV Spectrometer
6 MeV Spectrometer

4. Baseline Parameters
Injector Design : 1nC , laser pulse 10ps square ,  < 1 mm-mrad
2007 Commissioning baseline parameters
Limits
Q ≤ 500pC
Repetition rate ≤ 30Hz
Gun gradient ≤ 120 MV/m
Risk lower than for the design parameters
0.5 nC requires only QE of 10-5 with laser energy of 250 J
Getting to  < 1 mm-mrad not as challenging
for charges < 0.5 nC laser pulse length of 10 ps ( when radius can be adjusted)
Less sensitivity to parameters variation Q
objective 
Laser Pulse length
Laser Pulse radius
0.2 nC
0.85 mm-rad
10 ps
Variable [0.35 , 1.5 ] mm
0.5 nC
~ 1 mm-rad
Variable [0.55 , 1.5 ] mm

5. Strategy (Reminder) 1st Pass : beam to 135 MeV
Start-up equipment to reach 135 MeV
Software checkout
2nd Pass : first order optics
Steering
Matching
3rd Pass :
Characterization:
Transverse emittance (slice & projected)
Longitudinal phase space (slice energy spread)
Optimization :
Fine tuning of gun-solenoid
Scan of parameters (solenoid fields, phases, voltages …)
135 MeV spectrometer
6 MeV spectrometer
6 MeV transverse

6. Injector Layout RF Gun L0a RF section L0b RF section gun spectrometer
6 MeV
L0b RF section
62 MeV
gun spectrometer
Transverse RF deflector
135 MeV
L1 RF section
(21-1b)
main SLAC Linac
injector spectrometer
sector 20
sector 21

7. Longitudinal Phase Space at TCAV
135 MeV spectrometer
Direct Longitudinal Phase Space measurement
Transverse deflecting cavity  y / time correlation
(with V = 1MV, 0.5mrad over 10ps )
Spectrometer  x / energy correlation
Resolution requirements : 7m
OTRS1 with 11m resolution ok
D = 0.9m ,  = m (1) nominal matching
 = m (2) modified tuning
DL1
Longitudinal Phase Space at TCAV
135 MeV
Spectrometer
Spectrometer Screen

8. resolution 6 keV for nominal optics
resolution 3 keV for modified optics
3keV -> 40 keV will be measurable
rms
Direct Measurement
Projection

9. 6 MeV Spectrometer Energy Correlated Energy Spread
QG02
YAG01
QG03
YAGG1
Energy
Absolute energy
Distinguish rf  Vrf
Correlated Energy Spread
Slice thermal emittance
Relay imaging system from YAG01 to spectrometer YAGG1
Uniformity of line density

10. Horizontal Projection Linear Scaling of Energy atYAG01
High Charge operation
Temporal pulse , … using quadrupoles to project on manageable size screen
Tail
Horizontal Projection
Linear Scaling of Energy atYAG01
8% modulation
on laser pulse
at YAG01 Location
at YAGG1

11. 6 MeV Transverse Measurements
QE (charge to laser energy)
Charge vs Gun RF phase
QE vs x,y position laser on cathode
Building thermal emittance model
Cathode Uniformity
Point-to-Point Imaging
Uniformity of emission disk
Ellipticity + Slope of Edges
Thermal emittance measurement
Infinite-to-Point imaging
Divergence at cathode
Distribution of p
Cross-check Energy meas.
Using Steerer: beam to YAG02
Rotation angle of mask image
YAG01
YAG02
FC01

12. Cathode Imaging Point-to-point imaging of cathode
Cathode Image at DUVFEL
Virtual cathode
Virtual cathode
Direct determination
Uniformity of emission
Ellipticity
Transv. rise/fall slopes
e image : hot spot
electrons image
Getting initial conditions. Use complementary laser image for init distribution. Find image point of ebeam. Measure emitted distribution. Use in simulations.
Courtesy W.Graves

13. Cathode emittance
cathode (with appropriate set of Vrf, rf, Bsolenoid)
Momentum distribution
Assumes cathode = 0.6 mm.mrad
Image of divergence of source
At YAG2 , with Vrf reduced

14. Risk : Laser Pulse shape
Difficult to meet specifications
Rise time 1 ps
Uniformity 10% ptp
Pulse stacker
Pulse with 2-3 gaussians give satisfactory performances
Even better for compression (flatter at 135 MeV )
= 1.7 ps
= 1.15 ps
Dis./  [1nC] p
80
<10,90>
(2) Gaussians
1.41
1.23
0.97
(3) Gaussians
1.24
1.11
0.91
“Square”
1.08
0.84

15. Risk : Gun field
if 120MV/m difficult (breakdowns and large dark current)
110 MV/m gives performances very similar to 120 MV/m
100 MV/m is also gives acceptable performances (see next slide)
( for 0.5 nC, 80 < 0.8 mm-mrad )
Q [nC]
Laser pulse
Gun Field
80 mm-mrad
proj.mm-mrad
z [mm]
0.2
6.5 ps
120 MV/m
0.35
0.44
0.657
110 MV/m
0.37
0.704 1 10
0.91
1.08
0.948
0.95
1.05
0.97 12
0.92
1.02 14
0.88
1.157

16. 100MV/m, 2 Gaussians, 0.5 nC < {10,90} > ~ 0.7 mm-mrad
Parameters improved by using
a 0.6 mm radius beam
80 ~ 0.78 mm-mrad
< {10,90} > ~ 0.6 mm-mrad

17. Risk: Solenoid Alignment
Tolerance : 250 m, 250rad w.r.t to gun electrical axis
Requires beam based alignment
1) Determine center of cathode
2) Determine error in solenoid position with as few steps of solenoid motion
F(X, rf, Vrf, Bsol, Xsol) = Xf
4 unknowns Xsol = (x,x’,y,y’)
Center BPM/Screen cannot be determined with beam
Angle resolution from BPM2-BPM3 > 100 rad
Code
Single Particle tracking in Matlab for on-line modeling
gun to L0a (including misalignment of components + earth magnetic field)
to be extended to DL1 (i.e linacs + quads)
Solenoid
SC0
SC1
SC2
Gun
BPM2
BPM3
L0a
BPM5

18. Risk: Solenoid Alignment
1) Center of cathode
Steer laser centroid on 2D grid
Scan Gun RF phase
Gun
YAG02
Centroid on cathode
Centroid on YAG01, rf [24,36]

19. Risk: Solenoid Alignment
2) Mispositioning Solenoid
(Position, Angle ) does not vary with strength when the Solenoid aligned Vary Solenoid strength
Algorithm
A- Assume center cathode known to better than 50 m
B- Assume axis gun on screen is known within 50 m
C- Requires at least 8 motions of solenoid
Issues:
Too little light on single pulse
when solenoid field small
Only explore small Bz range
Model based needs to use
variation of phase

20. Risk: Optimization Scan parameters : (rf, Vrf , B solenoid)
Large Variation of betatron function while varying Bsolenoid
Rematching necessary for emittance measurements
3 screen emittance : best resolution for perfect parabola
(with 2 = ½ 1 = ½ 3 )

21. Matching performed for each point Tuned to matching of -0.6% case

22. Conclusions 135 MeV spectrometer 6 MeV spectrometer
Thermal emittance model
Risks :
Pulse shaping : stacker with 2-3 gaussians
Gun at 100 MV/m
Optimization : rematching necessary
Solenoid alignment in minimum steps
… ?
Which other risks are we missing ?

23. BACK-UP

24. Imaging source divergence what type of momentum distribution?
Momentum at cathode
Imaging source divergence what type of momentum distribution?

25. Injector Diagnostics YAG screen RF Gun trajectory (BPMs)
emittance (+ slice)
energy spread (+ slice)
bunch length (+ dist.)
charge (+ dark current)
YAG screen
YAG screen
YAG
screen
YAG screen
gun spectrometer
Transverse RF deflector
OTR & wire
Injector Diagnostics
OTR & wire
OTR & wire
OTR & wire
main SLAC Linac
injector spectrometer
YAG
YAG & OTR

26. Verifications on baseline case
Deck updated with all engineering constraints
Lost some margin on the emittance growth budget
Standard quiet start , 100k
With the modified quiet start
beam uniform transversally
but with ring structure weighted to 1
100k
SOL1 had to be increased by +0.5% from above case

27. Modeling Transverse Profile
Apply “quiet start” on square and extract rings
Number of particles per square chosen to match transverse charge density

29. Modeling Transverse Profile
Case of ~ 30% peak-to-peak
Optimization: scan solenoid 1
Minimum SOL at +1% , p ~1.2 mm-mrad , 80 ~1.0 mm-mrad
uses all the error budget
But, <10,90> ~0.92 mm-mrad

30. Modeling Transverse Profile
Case of 60% peak-to peak
80 just hardly meets 1.1 mm-mrad
<  (10,90) > hardly meets 1mm-mrad

31. Modeling Transverse Profile
Case of 20% peak-to peak
80 ~ 0.94 mm-mrad , <  (10,90) > ~ 0.85 mm-mrad

32. Summary Transverse profile
projected
[mm-mrad]
80%
<10,90 >
Ref.
1.04
0.94
0.85
Modified Quiet Start
0.95
0.86
20% ptp
1.15 (1.07)
0.92 (0.97)
0.84 (0.87)
30% ptp
1.23 (1.15)
0.99 (1.04)
0.92 (0.96)
60% ptp
1.23
1.10
1.03

34. More Profile measurement
Standard “Beer Can”
“3D-Ellipsoid”

35. Cathode Imaging Point-to-point imaging of cathode
Cathode Image at DUVFEL
Virtual cathode
Virtual cathode
Direct determination
Uniformity of emission
Ellipticity
Transv. rise/fall slopes
e image : hot spot
electrons image
Result Correlated to
E gun
Solenoid calibration
(from mask image rotation )
Getting initial conditions. Use complementary laser image for init distribution. Find image point of ebeam. Measure emitted distribution. Use in simulations.
Courtesy W.Graves

36. Cathode emittance Direct determination
cathode (with appropriate set of Vrf, rf, Bsolenoid)
Momentum distribution
 Fundamental for initial model + cathode quality
Correlated quantities
E gun
Solenoid calibration
Assumes cathode = 0.6 mm.mrad
Image of divergence of source
At YAG2 , with Vrf reduced

37. Imaging source divergence what type of momentum distribution?
Momentum at cathode
Imaging source divergence what type of momentum distribution?

38. More Profile measurement
Standard “Beer Can”
“3D-Ellipsoid”

39. Alignment Procedure Find cathode center first
(electrical center of gun)
Scan gun phase while scanning laser position
Length and curvature of position at screen give cathode center
Center found to within +/-100um

40. Aligning Solenoid Procedure Constraints
Assumes RF center on screens are known
Scan Bz for different laser pos. on cathode
Constraints
Need to align with few moves of solenoid
4 parameters to be determined in a 2-D space
Many combinations of xs,xs’,ys,ys’ give indistinguishable focus

41. Model-Based Approach
Distinguish overlapping combinations by modeling all possibilities.
In examples below, scanning Bz and cathode x position distinguish different cases.

42. Linearity of Solenoid Misalignment
Linear relationship holds throughout spec region

43. 100MV/m, 2 Gaussians, 0.5 nC < {10,90} > ~ 0.7 mm-mrad
Parameters improved by using
a 0.6 mm radius beam
80 ~ 0.78 mm-mrad
< {10,90} > ~ 0.6 mm-mrad

44. Gun Characterization QE, thermal, Uniformity Emission , Bunch Length
YAG1
YAG2
CR1
YAGG1
CRG1

45. Courtesy J.Schmerge, GTF
QE from Schottky Scan
Direct determination of QE
RF for a given Vrf
Courtesy J.Schmerge, GTF

46. Solenoid = 98 A Data Parmela Solenoid = 104 A Solenoid = 108 A
DUVFEL EXPERIMENT
Good match of Slice Emittance and Twiss Parameters
Parameters: 200 pC
Solenoid = 104 A
Solenoid = 108 A

47. Difficulties of Calibrations
 beam at YAG1 varies with Vrf , rf , Gun field balance, charge, Solenoid calibration
calibrate Vrf , rf (see slide 18-20)
then can possibly detect field unbalanced
Fit of DUVFEL measurements

48. Diagnostics Current Monitors Straight Ahead Spectrometer Wire scanners
Cerenkov Radiator
OTRs
YAGs
Gun
Spectrometer
EO monitor

49. Including Magnets
Treaty Point

50. 1 2 3 4 Linac tunnel ‘Laser Heater’ Straight Ahead Spectrometer
3 screen emittance measurement
‘RF Deflecting cavity’ TCAV1
Emission
thermal
Uniformity QE 2 3 4
Gun Spectrometer

51. 3 screen emittance measurement ‘RF Deflecting cavity’ TCAV1
6 MeV
 = 1.6 m
,un. = 3keV
63 MeV
 = 1.08 m
,un. = 3keV
135 MeV
 = 1.07 m
,un. = 3keV
135 MeV
 = 1.07 m
,un. = 40keV
Linac tunnel
‘Laser Heater’
Gun S1 S2
L0-1
19.8MV/m
L0-2
24 MV/m
DL1
Spectrometer
3 screen emittance measurement
‘RF Deflecting cavity’ TCAV1
Spectrometer
UV Laser 200 J,  = 255 nm, 5-20 ps, r = mm

52. Diagnostics Current Monitors EO monitor Cerenkov Radiator YAGs OTRs
Faraday Cup
EO monitor
Cerenkov Radiator
YAGs
OTRs
Wire scanners
Gun
Spectrometer
Straight Ahead Spectrometer

53. Injector Layout RF Gun L0a RF section L0b RF section gun spectrometer
6 MeV
L0b RF section
62 MeV
135 MeV
gun spectrometer
Transverse RF deflector
injector spectrometer
main SLAC Linac
sector 20
sector 21

54. Risk: Solenoid Alignment
2) Error of solenoid position
F(Xlaser, rf, Vrf, Bsol, Xsol) = Xf
Large systematic errors on Xf (reference 0 cannot be determined)
F(Xlaser, rf, Vrf, Bsol, Xsol) = Xf - Xf0
Determining Xsol is a very non-linear problem
Xsol = (xsol, xp,sol, ysol, yp,sol)
Xf reference (Xf0, Xfp0, Yf0,Yfp0)
 8 unknowns instead of 4

55. Risk: Solenoid Alignment
2) Error of solenoid position
Single Particle tracking in Matlab for on-line modeling ( similar to V-code)
gun to L0a (including misalignment of components + earth magnetic field)
to be extended to DL1 (i.e linacs + quads)
Algorithm to determine, in minimum steps, mis-positioning of the solenoid
F(X, rf, Vrf, Bsol, Xsol) = Xf
Issue :
4 unknowns Xsol = (x,x’,y,y’)
Center BPM/Screen cannot be determined with beam
BPMs too close together for good accuracy on angle
Angle resolution from BPM2-BPM3 > 100 rad
But Indirect evaluation of angle using BPM5
Only solution: model based analysis for complicated non-linear problem
Solenoid
SC0
SC1
SC2
Gun
BPM2
BPM3
L0a
BPM5

56. 100MV/m, 2 Gaussians, 0.5 nC < {10,90} > ~ 0.6 mm-mrad
With 0.6 mm radius beam
80 ~ 0.78 mm-mrad
< {10,90} > ~ 0.6 mm-mrad
Large margin for emittance increase from errors

57. Emittance Projected : containing all particles
 80 : projected for the 80 central slices
<  10,90 > : average of slice emittance for slices from 10 to 90