Linac Physics, Diagnostics, and Commissioning Strategy P 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-nC charge, 1.2-mm slice emittance, 120-Hz repetition rate… 6 MeV z 0.83 mm 0.05 % 135 MeV z 0.83 mm 0.10 % 250 MeV z 0.19 mm 1.6 % 4.54 GeV z 0.022 mm 0.71 % 14.1 GeV z 0.022 mm 0.01 % Linac-X L =0.6 m rf= -160 rf gun new Linac-1 L 9 m rf -25° Linac-2 L 330 m rf -41° Linac-3 L 550 m rf -10° Linac-0 L =6 m ...existing linac 21-1b 21-1d X 21-3b 24-6d 25-1a 30-8c undulator L =130 m BC-1 L 6 m R56 -39 mm BC-2 L 22 m R56 -25 mm DL-1 L 12 m R56 0 LTU L =275 m R56 0 SLAC linac tunnel research yard (RF phase: frf = 0 is at accelerating crest) P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Complete & Detailed Design (cathode to dump) BC2 L3 LTU cathode undulator P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
after BC1 after X-RF after L1 after DL1 after BC2 after L3 at und. (2002 example) after BC1 after X-RF after L1 after DL1 after BC2 after L3 at und. after L2 energy profile phase space time profile sz = 830 mm sz = 190 mm sz = 830 mm sz = 23 mm sz = 830 mm sz = 23 mm sz = 190 mm sz = 23 mm P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Location of Main Linac Diagnostics 5+ energy spread meas. stations (optimized with small b) 5+ emittance meas. stations designed into optics (Dyx,y) BPMs at or near most quadrupoles and in each bend syst. RF deflectors for slice e and sE measurements (L0 & L3) rf gun T-cav. gex,y T-cav. L0 gex,y gex,y gex,y gex,y ...existing linac L1 X L2 L3 sE sE sE E E E sE sE E E P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Linac ‘Commissioning’ (Physics) How to setup Ipk = 3.4 kA, 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 Will show a few examples P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Setup of Linac-0 RF minimize energy spread with L0 RF phase sy = bunch length Approximate injector parameters needed prior to linac commissioning. RF-deflector at 1 MV minimize energy spread with L0 RF phase RF-deflector Phasing L0-Linac P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
(X-band off, BC1 bends at 295 MeV) Setup of Linac-1 RF 20-mm res. BC1 BPM 20-mm res. BC1 BPM LX RF phase L1 RF phase Linac-1 RF phase scan (X-band off, BC1 bends at 295 MeV) Linac-X RF phase scan (BC1 bends at 250 MeV) set phase to -25˚0.5˚ set phase to -160˚0.5˚ Linac-1 new rf gun 21-1b 21-1d X Turn on BC1 energy feedback Switch off BC2 chicane Use sec-25 RF-deflector to meas. bunch length (sz1) Adjust S-band RF phase (0.5˚) to set sz1 195 10 mm P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Verify BC1 Setup (NO CSR) Scan Linac-1 S-band RF phase and use BC2 BPM to find maximum wake-induced energy loss across Linac-2 rf gun L1 X L2 well tested at SPPS P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
(BC2 bends at 5.3 GeV, 2 klys. off) Setup of Linac-2 RF 40-mm res. BC2 BPM 5-mm res. LTU BPM (NO CSR) L2 RF phase L2 phase Linac-2 RF phase scan (BC2 bends at 5.3 GeV, 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˚ Turn on BC2 energy feedback Use sec-25 RF-deflector to measure length (sz2) Adjust L2 RF phase (0.5˚) to set sz2 20 2 mm Linac-3 phasing is trivial (5˚) L2 L3 P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Emittance Meas. Simulation in LCLS Multiple OTR screens Multiple wire-scanners Quad-scans on single OTR Quad-scans on OTR with RF-deflector OTR1,2,3 WS11,12,13 BC1 P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
135-MeV x-profiles (from tracking) sx 118 mm sx 49 mm sx 120 mm non-Gaussian gex = 0.75 ± 0.04 mm P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Slice-Emittance Measurement Simulation sy bunch length RF-deflector at 1 MV slice OTR 10 times 135 MeV quad scanned P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Slice-Emittance Measurement Simulation (slice-y-emittance also simulated in BC1-center) Injector (135 MeV) with S-band RF-deflector at 1 MV = meas. sim. = calc. = y distribution = actual (same SLAC slice-e code used at BNL/SDL) DL1 slice-emit on WS02 slice-5 P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Empirical BC1/BC2 Dispersion Correction actual data from SPPS chicane Dx /2 Residual x-dispersion (and its angle) is precision minimized using ‘tweaker’ quads in the chicane SPPS chicane with quads 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) (310-5 & 10-4) + collimation 4 e-wires, 6 collimators, 1 OTR 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 P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Slice-Emittance Configuration for LTU nominal optics (proj. emit.) WS31-34 undulator… slice-emit. meas. optics stopper inserted OTR33 P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Slice-Emittance Measurements in LTU LTU at 14 GeV with S-band RF-deflector at 24 MV x z x = meas. sim. = calc. = y distribution = actual y P. Emma, SLAC LCLS DOE Review – Aug. 12, 2004
Slice Energy Spread Measurements in LTU LTU at 14 GeV with S-band RF-deflector at 24 MV sE/E 10-4 DE/E0 z sx 12 mm x 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 (1st 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