Linac Design Update P Emma LCLS DOE Review

Linac Design Update P. Emma LCLS DOE Review May 11, 2005 LCLS 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Linac Design is Mature and Stable Single bunch, 1 -n. C charge, 1. 2 -mm slice emittance, 120 -Hz repetition rate… 6 Me. V z 0. 83 mm 0. 05 % 250 Me. V 4. 30 Ge. V z 0. 19 mm z 0. 022 mm 1. 6 % 0. 71 % Linac-X L =0. 6 m rf= -160 Linac-1 Linac-2 Linac-3 L 9 m L 330 m L 550 m rf -25° rf -41° rf -10° 135 Me. V z 0. 83 mm 0. 10 % rf gun w ne Linac-0 L =6 m . . . existing linac DL-1 L 12 m R 56 0 21 -1 b 21 -1 d X BC-1 L 6 m R 56 -39 mm 21 -3 b 24 -6 d SLAC linac tunnel BC-2 L 22 m R 56 -25 mm 13. 6 Ge. V z 0. 022 mm 0. 01 % undulator L =130 m 25 -1 a 30 -8 c LTU L =275 m R 56 0 research yard (RF phase: frf = 0 is at accelerating crest) 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

New Since Last Review Optional low-charge operating point (0. 2 n. C) Laser-heater low FEL gain “lock-in” detection Bunch length & energy feedback simulations Dark current, beam loss, and collimation study complete Detailed linac tuning simulations done Engineering constraints worked into design 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Low Charge Operating Point (1) Motivation: Less charge less wake Same compression factor ~same jitter Lower gun current lower emittance Chosen Scaling: Charge: 1 n. C 0. 2 n. C Gun Current: 100 30 A (10 ps 6. 5 ps) Sliced gun emittance: 1 mm 0. 8 mm Final current: 3 k. A 2 k. A (same Lsat) 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

gex, y (mm) Low Charge Operating Point (2) gex, y (mm) rms errors: 300 -mm struct. 200 -mm quad 200 -mm BPM steer 10 seeds 1. 0 n. C 0. 2 n. C Linac Alignment Eased 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Low Charge Operating Point (3) 0. 2 n. C 1 n. C Bane/Stupakov AC-conductivity model 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Low Charge Operating Point (4) 1012 photons B. Fawley, S. Reiche 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Low Charge Operating Point - Summary BC 2 CSR De 1/5 Linac quad/BPM align. tol. ’s 2 L 2 transverse wake De 1/16 Peak current jitter ½ X-ray pulse 80 fs (was 200 fs) Weak undulator RW-wake FEL power: 20 GW & ~1012 photons 1 -n. C operation still fully supported 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Low FEL Gain ‘Lock-in’ Detection* (1) Simulate LCLS (Linac + M. Xie) with: Linac jitter (DQ, t 0, f, V, etc. ) Large emittance (3 mm) low gain Spontaneous radiation background Laser-heater modulated at 7 Hz Use FFT to ‘lock-in’ on very weak FEL signal in spont. background * Idea from K. Robinson and comments by J. Rossbach (FAC, April 2004) 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Low FEL Gain ‘Lock-in’ Detection (2) E PFEL at 13. 6 Ge. V 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Low FEL Gain ‘Lock-in’ Detection (3) total signal Gain of ~25 detectable spontaneous signal FEL signal FFT of total signal PAC’ 05 paper: (P. E. , Z. Huang, J. Wu) 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Bunch Length and Energy Feedback OFF Feedback ON Juhao Wu (SLAC) 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Dark Current, Beam Loss, Collimation (1) Model cathode dark current (Fowler-Nordheim and Parmela), scaling charge from GTF measurements Add dark current in critical RF structures along linac, based on K. Bane work in NLC (a non-issue) Track dark current through linac and through und. Include aperture restrictions and collimators Assess collimation scheme in terms of undulator protection and average power loss on collimators Evaluate wakefield effect of each collimator PE, J. Wu 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Dark Current, Beam Loss, Collimation (2) 1 new BC 2 E-coll. 36 -mm ( = 10%) BC 1 2 new E-coll. 2. 5 mm ( = 2%) BC 2 1 new BC 1 E-coll. 45 -mm ( = 20%) undulator 4 existing x-coll. ’s 4 existing y-coll. ’s 1. 6 & 1. 8 mm 2. 4 p. C/pulse 3. 3 W (120 Hz, 11. 3 Ge. V) 3 new x-coll. ’s 3 new y-coll. ’s 2. 2 mm… 1. 0 p. C/pulse 0. 2 p. C/pulse 1. 6 W (120 Hz, 0. 3 W (120 Hz, 13. 6 Ge. V) DE/E of 1 dropped klystron = -1. 7% 11 May 2005 LCLS DOE Review under ground P. Emma@SLAC. Stanford. edu

Dark Current, Beam Loss, Collimation - Summary Undulator is protected from gun and structure dark current Maximum collimated beam power in ‘aboveground’ section is 0. 3 W (well below safe level) Results still look safe even for 10 -times more dark current (but already used worst-case GTF) Collimator wakefields should not be an issue (~0. 5 -mm alignment tolerances) Shower calculations were done (20 W/coll. was assumed, now ~70 -times smaller) 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Linac Tuning Simulations (1) Start with low-charge (0. 2 n. C, no CSR) Use elegant to automate tuning; use only ‘real’ diagnostics Add large errors to linac systems (e. g. , magnets, RF, beam) Assume rough corrections already made (see LCLS Commissioning Workshop, Sep. 2004) Track through linac many times, each step simulating one particular correction (e. g. , b-matching or RF phasing) Use correction devices already built into design (e. g. , BC 2 correction quads, trajectory controls) Evaluate final beam quality, correction convergence, dynamic range, problem areas, etc. 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Linac Tuning Simulations (2) rms errors (Gaussian, 3 -s cutoff) x and y misalignments z misalignments Quads relative gradient errors roll angle errors relative field errors Bends anomalous field gradients (BC’s) BPMs x and y misalignments RF strucs. phase errors (static) relative voltage errors (static) e- beam random charge error initial beta mismatch in x and y Element 11 May 2005 LCLS DOE Review value 300 5 0. 5 2 0. 5 0. 3 3 300 2 1 10 2. 0 unit mm mm % mrad % tol. mm mm deg % % P. Emma@SLAC. Stanford. edu z

Linac Tuning Simulations (3) 0. 2 n. C before tuning gex, y 1. 4 mm zx = 3. 3 ! 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Linac Tuning Simulations (4) after tuning gey= 0. 91 mm gex = 0. 88 mm zx, y 1 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Linac Tuning Simulations (5) DESIGN TUNEUP 2 k. A 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu

Comments System in mature, well studied, and reasonably ready for construction Many more slides are available to answer questions 11 May 2005 LCLS DOE Review P. Emma@SLAC. Stanford. edu