Linac Physics Diagnostics and Commissioning Strategy P Emma

Linac Physics, Diagnostics, and Commissioning Strategy P. Emma LCLS DOE Review August 12, 2004 LCLS P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004

Nominal LCLS Linac Parameters for 1. 5 -Å FEL 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. 54 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 BC-2 L 22 m R 56 -25 mm SLAC linac tunnel (RF phase: frf = 0 is at accelerating crest) P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004 25 -1 a 30 -8 c 14. 1 Ge. V z 0. 022 mm 0. 01 % undulator L =130 m LTU L =275 m R 56 0 research yard

Complete & Detailed Design (cathode to dump) cathode P. Emma, SLAC L 2 BC 2 L 3 LCLS DOE Review – Aug. 12, 2004 LTU undulator

(2002 example) after L 2 energy profile phase space after DL 1 time profile z = 830 mm after L 1 z = 190 mm after BC 2 z = 830 mm after X-RF z = 23 mm after L 3 z = 830 mm after BC 1 at und. z = 190 mm P. Emma, SLAC z = 23 mm LCLS DOE Review – Aug. 12, 2004 z = 23 mm

Location of Main Linac Diagnostics 5+ energy spread meas. stations (optimized with small b) 5+ emittance meas. stations designed into optics (D x, y) BPMs at or near most quadrupoles and in each bend syst. RF deflectors for slice e and E measurements (L 0 & L 3) rf gun T-cav. L 0 gex, y L 1 . . . existing linac E E P. Emma, SLAC gex, y T-cav. L 2 X E E L 3 E E LCLS DOE Review – Aug. 12, 2004 gex, y E E

Linac ‘Commissioning’ (Physics) How to setup Ipk = 3. 4 k. A, ge 1. 2 mm, etc. What to measure and what to adjust Longitudinal phase space Bunch Length Energy Spread (proj. & slice) Transverse phase space Projected Emittance Slice Emittance Feedback Systems P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004 Will show a few examples

Setup of Linac-0 RF Approximate injector parameters needed prior to linac commissioning. y = bunch length RF-deflector at 1 MV minimize energy spread with L 0 RF phase RF-deflector Phasing L 0 -Linac P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004

Setup of Linac-1 RF 20 -mm res. BC 1 BPM LX RF phase L 1 RF phase Linac-1 RF phase scan (X-band off, BC 1 bends at 295 Me. V) Linac-X RF phase scan (BC 1 bends at 250 Me. V) set phase to -25˚ 0. 5˚ set phase to -160˚ 0. 5˚ rf gun w ne Linac-1 21 -1 b 21 -1 d P. Emma, SLAC X Turn on BC 1 energy feedback Switch off BC 2 chicane Use sec-25 RF-deflector to meas. bunch length ( z 1) Adjust S-band RF phase ( 0. 5˚) to set z 1 195 10 mm LCLS DOE Review – Aug. 12, 2004

Verify BC 1 Setup (NO CSR) Scan Linac-1 S-band RF phase and use BC 2 BPM to find maximum wake-induced energy loss across Linac-2 rf gun well tested at SPPS P. Emma, SLAC L 1 X LCLS DOE Review – Aug. 12, 2004 L 2

40 -mm res. BC 2 BPM Setup of Linac-2 RF 5 -mm res. LTU BPM (NO CSR) L 2 RF phase L 2 phase Linac-2 RF phase scan (BC 2 bends at 5. 3 Ge. V, 2 klys. off) Scan Linac-2 phase & use LTU BPM to find max. wake-induced energy loss across Linac-3 set phase to -41˚ 0. 5˚ L 2 P. Emma, SLAC L 3 Turn on BC 2 energy feedback Use sec-25 RF-deflector to measure length ( z 2) Adjust L 2 RF phase ( 0. 5˚) to set z 2 20 2 mm Linac-3 phasing is trivial ( 5˚) LCLS DOE Review – Aug. 12, 2004

Emittance Meas. Simulation in LCLS Multiple OTR screens Multiple wire-scanners OTR 1, 2, 3 P. Emma, SLAC Quad-scans on single OTR Quad-scans on OTR with RF-deflector BC 1 LCLS DOE Review – Aug. 12, 2004 WS 11, 12, 13

135 -Me. V x-profiles (from tracking) x 118 mm x 49 mm x 120 mm non-Gaussian gex = 0. 75 ± 0. 04 mm P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004

Slice-Emittance Measurement Simulation RF-deflector at 1 MV slice OTR 10 times 135 Me. V quad scanned P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004 sy bunch length

Slice-Emittance Measurement Simulation (slice-y-emittance also simulated in BC 1 -center) Injector (135 Me. V) with S -band RF-deflector at 1 MV (same SLAC slice-e code used at BNL/SDL) = meas. sim. = calc. = y distribution = actual DL 1 slice-emit on WS 02 slice-5 P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004

Empirical BC 1/BC 2 Dispersion Correction actual data from SPPS chicane D x /2 Residual x-dispersion (and its angle) is precision minimized using ‘tweaker’ quads SPPS chicane with quads in the chicane Correct h and (ah + bh ), orthogonally with 2 quads P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004

Linac-To-Undulator (LTU) vertical bends energy centroid & spread meas. (OTR) (3 10 -5 & 10 -4) + collimation 4 e-wires, 6 collimators, 1 OTR P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004 · · · · vertical bend 4. 7 mr horizontal jog 1. 25 m energy diagnostics emit. diagnostics bunch length diag. collimators CSR cancellation branch points for future undulators · spontaneous undulator possible

Slice-Emittance Configuration for LTU nominal optics (proj. emit. ) WS 31 -34 undulator… slice-emit. meas. optics OTR 33 P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004 stopper inserted

Slice-Emittance Measurements in LTU x LTU at 14 Ge. V with S-band RF-deflector at 24 MV x z y P. Emma, SLAC = meas. sim. = calc. = y distribution = actual LCLS DOE Review – Aug. 12, 2004

DE/E 0 Slice Energy Spread Measurements in LTU E/E 10 -4 LTU at 14 Ge. V with S-band RF-deflector at 24 MV z x sx 12 mm FEL goal y P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004

LCLS Longitudinal Feedback Simulation Feedback OFF Feedback ON Juhao Wu (SLAC) P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004

Summary LCLS linac is operationally flexible Diagnostics have been incorporated into optical design and simulated (1 st pass) Two RF-deflectors allow time-resolved measurements at low and high energy Tune-up algorithms have been considered, but more work is needed Feedback system simulations show energy, peak current, and timing are stabilized Work continues P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004