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

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

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

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

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

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

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

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

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

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

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

Benchmarking Parmela GTF data are well reproduced by Parmela Parameters Cathode Field = 110MV/m gun  40 r = 1mm Bsolenoid  2kG Linac Gradient = 8.55 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

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

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