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LCLS

Experience at LCLS Towards Brighter Beams P. Emma, for The LCLS Commissioning Team LBNL X-Ray FEL Workshop October 23, 2008. Brief Commissioning Status CSR Measurements vs. Codes Stability Measurements Very Low Charge Operations Ultra-Low Emittance Ultra-Short Pulse Possibilities. LCLS.

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LCLS

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  1. Experience at LCLS Towards Brighter BeamsP. Emma, forThe LCLS Commissioning TeamLBNL X-Ray FEL WorkshopOctober 23, 2008 • Brief Commissioning Status • CSR Measurements vs. Codes • Stability Measurements • Very Low Charge Operations • Ultra-Low Emittance • Ultra-Short Pulse Possibilities LCLS

  2. Injector (35º) at 2-km point Existing 1/3 Linac (1 km) (with modifications) New e- Transfer Line (340 m) X-ray Transport Line (200 m) Undulator (130 m) Near Experiment Hall Far Experiment Hall Linac Coherent Light Source at SLAC X-FEL based on last 1-km of existing linac 1.5-15 Å

  3. beam parked here Nov 2008… Commission Jan-Aug 2008 Commission Mar-Aug 2007 LCLS Accelerator Layout 250 MeV z  0.19 mm   1.6 % 4.30 GeV z  0.022 mm   0.71 % 13.6 GeV z  0.022 mm   0.01 % 6 MeV z  0.83 mm   0.05 % 135 MeV z  0.83 mm   0.10 % Linac-X L =0.6 m rf= -160 Linac-0 L =6 m rf gun L0-a,b Linac-3 L 550 m rf  0° Linac-1 L 9 m rf  -25° Linac-2 L 330 m rf  -41° 25-1a 30-8c 21-3b 24-6d ...existing linac 21-1 b,c,d undulator L =130 m X BC1 L 6 m R56 -39 mm BC2 L 22 m R56 -25 mm undulator DL1 L 12 m R56 0 DL2 L =275 m R56  0 SLAC linac tunnel research yard X-rays in spring 2009

  4. Commissioning Highlights (2008) • Injector Commissioning: Apr-Aug, 2007 (DONE) • Phase-II Commissioning: Dec-Aug, 2008 (DONE) • Projected emittances 0.7-1.6 mm at 0.25 nC, 10 GeV • Routine 30-Hz e- to 14 GeV (~24/7 with ~90% up-time) • Bunch compression fully demonstrated down to 2 µm • CSR emittance growth measurements agree with codes • Electron bunch appears bright enough to drive 1.5-Å FEL • Cathode replaced with improved QE & thermal emittance • 20-pC bunch with 0.14-µm emittance (<10 fs length?) • Phase-III Commissioning (FEL): starts Nov. 3, 2008

  5. Projected Emittance <1.2 μm at 1 nC (135 MeV) OTR screen gex = 1.07 μm 1 nC 95% area cut Gaussian overlay not used gey = 1.11 μm

  6. Compression and CSR Energy Loss in BC1 at 0.25 nC A Phase shift of -0.4 deg is added to the Elegant curves Bunch length after BC1 measured with transverse RF Y. Ding, Z. Huang CSR energy loss after BC1 measured with BPM e- Elegant g Chicane Bend BPM

  7. Horizontal Emittance Growth after BC1 (250 MeV) at 0.25 nC sx = 38 mm sx = 55 mm sx = 246 mm j = -22º j = -26º j = -27º Y. Ding, Z. Huang Vertical emittance after BC1 vs. RF phase Hor. emittance after BC1 vs. RF phase

  8. Bunch Compression & CSR Measured after BC2 (0.25 nC) BC2 (4.3 GeV) TCAV (5.0 GeV) BSY (14 GeV) 550 m sz < 5 mm nominal sz 2 mm old screen used sz > 25 mm L2 4 wires

  9. The LCLS Laser Heater (135 MeV)will be ready in December suggested by Saldin et al. and J. Galayda

  10. Laser-Heater OTR screens (7) YAG screens (7) RF Gun Wire scanners (7) Solenoid Dipole magnets (8) Beam stoppers (2) L0a S-band RF acc. sections (5) Gun Spectrometer L0b Emittance Screens/Wires Emittance Screen/Wires RF Deflector L1S 2-km point in 3-km SLAC linac X-band RF acc. section BC1 135-MeV Spectrometer TD11 stopper 135 MeV 250 MeV RF Deflector (LOLA) + special lattice configuration in spectrometer allows fine measurement of time-sliced energy spread (to <6 keV) sE 6 keV rms (40 mm)

  11. Measured & Simulated Energy Jitter in LCLS BPM 1 = 22º gun L0 0 = 0 L1S L2 L3 3 = 0 2 = 36º DL1 (135 MeV) BC1 (250 MeV) BC2 (4.3 GeV) BSY (14 GeV) Energy Jitter after DL1 Energy Jitter after BC2 Q = 0.25 nC DE21/2/E0  0.03% sim. = 0.04% sim. = 0.08% DE21/2/E0  0.09% Energy Jitter at Linac Exit Energy Jitter after BC1 Simulation jitter: sim. = 0.04% DE21/2/E0  0.03% s-rms = 0.04º DV/Vs-rms = 0.04% x-rms = 0.1º DV/Vx-rms = 0.1% DQ/Qrms = 1.25% DE21/2/E0  0.06% sim. = 0.05%

  12. BPM Y Position (mm) TCAV OFF TCAV ON 9 mm rms 110 mm rms Dt±0.6 ps Measuring Bunch Arrival Time Jitter e- S-band (2856 MHz) BPM V(t) Q = 0.25 nC slope = -2.34 mm/deg Now measure BPM jitter both with transverse RF OFF, and then ON (at constant phase) Timing Jitter (w.r.t. RF) = (110 mm)/(2.34 mm/deg) = 0.047 deg  46 fsec rms

  13. g(exey)1/2 = 1.04 mm (3.3 days) May 24, 2008 00:01 to May 27 09:00 Emittance Near End of Linac Over Long Weekend long weekend run at 0.25 nC with no tuning

  14. M. Xie method, with wakes FEL Power 3D Gain Length Beam Appears Bright Enough for FEL Saturation at 0.15 nm Calculation based on measured end-of-linac projected emittance values, measured peak current, and design undulator parameters (assuming undulator alignment and 0.01% rms slice energy spread – not yet measurable)

  15. Time-sliced x-Emittance at Very Low Charge OTR screen with transverse deflector ON 0.14 µm 20 pC, 135 MeV, 0.6-mm spot diameter, 400 µm rms bunch length (5 A)

  16. Time-sliced x-Emittance at Very Low Charge vs. RMS Drive Laser Spot Size on Cathode Calculated Thermal Emittance of 0.5 µm/mm (D. Dowell) 20 pC, 135 MeV, 400 µm rms bunch length (5 A)

  17. sz 1 mm ? LiTrack (no CSR) 8 kA? Measurements and Simulations for 20-pC Bunch at 14 GeV Photo-diode signal on OTR screen after BC2 shows minimum compression at L2-linac phase of -34.5 deg. SIMULATED FEL PULSE Y. Ding 1.5 Å, 3.61011 photons Ipk = 4.8 kA ge 0.4 µm LCLS FEL simulation at 1.5 Å based on measured injector beam and Elegant tracking,with CSR, at 20 pC. Horizontal projected emittance measured at 10 GeV, after BC2, using 4 wire-scanners.

  18. Simulated 20-pC Bunch at 4.3 GeV Approaching a SingleLongitudinally Coherent Spike at 15 Å z = 25 m (power profile at z = 25 m varies from shot to shot due to noisy startup) 15 Å, z = 25 m, 2.41011 photons, Ipk = 2.6 kA, ge 0.4 µm Y. Ding 1.2 fs LCLS FEL simulation at 15 Å based on measured injector beam and Elegant tracking,with CSR, at 20 pC.

  19. Re-Design LCLS to Reduce Costs (1.5 Å) ? PSI FEL design is similar, except at higher charge (0.2 nC)

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