1. Simulations for the LCLS Photo-Injector C
Simulations for the LCLS Photo-Injector C.Limborg, SSRL / SLAC April 24, 2002
LCLS Photo-injector Simulations
Nominal tuning
Sensitivity study
Benchmarking Parmela
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

2. projected < 1.2 mm.mrad slice < 1.0 mm.mrad
RF Gun : 
E(MV)
Balance
 th
Goal:
projected < 1.2 mm.mrad
slice < 1.0 mm.mrad
for 80 slices out of 100
at 150MeV, for 1nC, 10ps pulse, and “jitter” errors
Optimization in 19 D
parameter space
Laser Beam:
Longitudinal
(length, rise time, flatness)
Transverse
(r, uniformity)
Energy  charge
Linac Solenoid :
Position
Length
Field
Linacs :
Position
Field
Spacing
Gun Solenoid :
Position
Length
Field
Matching
Section
Linac Center
Line
Sector 20 Linacs
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

3. Optimization of LCLS photo-injector
Preliminary tuning with Homdyn
then refined optimization with PARMELA-LANL
1nC, 10ps flat top (0.7 ps rise time), transverse uniform, th = 0.3 mm.mrad
For all above cases, projected less than 1 mm.mrad
Good margin for errors
Very similar projected values for 140MV/m gun
E (MV/m)
rspot size (mm)
laser / 0-cross.
Bsolenoid1 (kG)
L2-0 (MV/m)
Bsolenoid2(kG)
120
1.2
27.8
2.71
18.5
0.8
p = projected
10k, 0.7 ps rise
> 100k, 0.7 ps
>100k, 0.35ps
th = 0.3 mm.mrad
p = 0.93 mm.mrad
p = 0.92 mm.mrad
p = 0.80 mm.mrad
th = 0.5 mm.mrad
p = 0.96 mm.mrad
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

4. Units as indicated with colors
Nicely converging beam
No emittance growth in Matching Section due to space charge
when aspect ratio of beam is 10:1 ; checked with 3D Parmela-LANL computation
Units as indicated with colors
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

5. slice rad for 100 slices  slice for 99 slices
97% part. i < 1 mm.mrad
95% part. i < 0.9 mm.mrad
71% part. i < 0.8 mm.mrad
Much better than
slice goal
slice rad for 100 slices
(ps) 
(ps)
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

6. Sensitivity study : Effect of individual parameters
Balance
3% is ok
Charge
 of 10% ok
Gun field
 < 0.5MV/m
Bsolenoid
 < 0.4% ok
Phase
3 ok
rspot size
0.1 mm ok
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

7. Sensitivity study: Combination of errors
Individual parameters increase emittance from 0.92 mm.mrad to 1.0 mm.mrad
E(MV/m)
120
Balance 1
o (S-band)
27.8
B (kG)
2.7079
r (mm)
1.2
Q(nC)
 0.5
 1.25 %
 3
 0.4%
 0.1
 5%
proj = 2.51 mm.mrad for worst combination
slice mm.mrad for 100 slices
(ps)
Run Number
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

8. Sensitivity study - Combination of errors (“jitter” type)
Variations included in simulations are larger than specifications
E(MV/m)
120
Balance 1
o (S-band)
27.8
B (kG)
2.7079
r (mm)
1.2
Q(nC)
 0.3
 3%
 0.5
 0.01%
 0.1
 2%
 = 1.25 mm.mrad for worst combination
slice mm.mrad for 100 slices ps
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

9. Sensitivity: Various Thermal emittances
slice (mm.mrad)
slice (mm.mrad)
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

10. Sensitivity: Rise time of pulse
Distribution density (a.u)
(mm.mrad)
Distributions are built from stack of Gaussians; rise time is rms of Gaussians
(th = 0.6 mm.mrad)
(ps)
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

11. Sensitivity: Transverse uniformity
Radial modulation of emission intensity on cathode spot
Rectangular grid (“checker”) to be studied with 3D
Reference deck includes longitudinal modulation,
r = 1mm; with uniform spot proj = 0.98 mm.mrad
proj increases by 10% when radial modulation is 40% peak-to-peak
Measurements on GTF cathode indicate less than 20% variation peak-to-peak in emission (See J.Schmerge “Experimental results”)
Laser Non-uniformity will be less than 20% (See P.Bolton “Laser”)
Emission Spot on
Cathode
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

12. Benchmarking Parmela GTF data are well reproduced by Parmela
Parameters
Cathode Field = 110MV/m
gun  40
r = 1mm
Bsolenoid  2kG
Linac Gradient = MV/m
Cathode-to-Linac Dist. = 90 cm
Gaussian Pulses
PARMELA 
Experiment 
Quad Scan with Parmela gives 20% smaller emittance with 5% truncation of tails
(similar truncation used in experiment)
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

13. Benchmarking Parmela Parmela in good agreements with experiments
Parmela explains results for 2ps and 4ps pulses
Booster mismatch worse for the 4 ps than for the 2ps
With 5.5 MV/m instead of 8.5 M/m => emittances reduce to 1.3 mm.mrad and 1.0 mm.mrad respectively for the 2ps and 4 ps cases at 300pC
Work under way
Systematic quad scan (computing contribution from space charge- See also J.Schmerge “Experimental results”)
Longitudinal booster phase scan (Longitudinal measurements)
Slice experiments analysis (both SLAC and BNL)
PIC codes
Good agreement Magic2D , Maxwell-T, PARMELA-LANL, PARMELA-UCLA
for test problem of first 40 ps leaving cathode
Full simulation of gun in collaboration with NLC team
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL

14. Conclusions LCLS Requirements are met for a 1nC, 10 ps pulse
Goal of  projected < 1.2 mm.mrad, slice < 1.0 mm.mrad is met with present design
With thermal = 0.5 mm.mrad
With combined errors meeting tolerance specifications
For non-uniformity of transverse spot size up to 40%
For longitudinal pulse with rise time < 0.7 ps
Confidence in Parmela
From good agreement with experimental results
From comparison with PIC codes
Plans for year
Finalize sensitivity study
Finalize comparison with PIC codes
Perform more comparisons with experiments
April 24, 2002, LCLS DOE Review,
C.Limborg SSRL