LCLS Commissioning Status

Transcription

1 LCLS Commissioning Status Paul Emma (for the LCLS Commissioning Team) June 20, 2008 LCLS ANL LLNL UCLA

2 FEL Principles Electrons slip behind EM wave by λ 1 per undulator period ( (λ u ) x K/γ e λ u v x E x > 0 Due to sustained interaction, some electrons lose energy, while others gain energy modulation at λ 1 e losing energy slow down, and e gaining energy catch up density modulation at λ 1 (microbunching) Microbunched beam radiates coherently at λ 1, enhancing the process exponential growth of radiation power λ 1 x-ray z v x E x > 0 0 Z. Huang

3 FEL Micro-Bunching Along Undulator electron beam photon beam undulator beam dump SASE* FEL starts up from noise * Self-Amplified Spontaneous Emission S. Reiche UCLA log (radiation power) distance

4 X-ray FEL requires extremely bright e beam Power grows exponentially with undulator distance, z but only if time-sliced energy spread <<10 3 and the transverse emittance is /4π. power gain length: is ~λ 1 /4 time-sliced emittance local peak current FEL power reaches saturation at ~20~ 20L G SASE performance depends exponentially on e beam quality (emittance & peak current!) Z. Huang

5 Slice versus Projected Emittance For a collider collision integrates over bunch length emittance projected over the bunch length is important For an FEL e slips back in phase w.r.t. photons by λ r per period, λ u λ u λ r FEL integrates over slippage length: slice emittance (and E-spread) is important Nλ r 0.5 μm

6 Linac Coherent Light Source at SLAC Å X-FEL based on last 1-km 1 of existing linac Existing 1/3 Linac (1 km) (with modifications) New e Transfer Line (340 m) Injector (35º) at 2-km 2 point X-ray Transport Line (200 m) Far Experiment Hall (underground) Undulator (130 m) Near Experiment Hall (underground) 14-GeV beam now commissioned

7 LCLS Design Parameters

8 LCLS Accelerator Schematic 6 MeV 135 MeV 250 MeV σ z 0.83 mm σ z 0.83 mm σ z 0.19 mm σ δ 0.05 σ δ 0.10 σ δ 1.6 Linac-0 L =6 m rf gun L0-a,b Linac-1 L 9 9 m rf 25 ϕ rf Linac-X L =0.6 m rf = 160 ϕ rf Linac-2 L 330 m rf 41 ϕ rf 4.30 GeV σ z mm σ δ 0.71 Linac-3 L 550 m rf 0 ϕ rf 13.6 GeV σ z mm σ δ existing linac DL1 L 12 m R b,c,d BC1 L 6 6 m mm R 56 Commissioned Mar-Aug 2007 X 21-3b 24-6d SLAC linac tunnel BC2 L 22 m mm R a 30-8c Commissioned Jan-Aug 2008 DL2 L =275 m 56 0 R 56 undulator L =130 m undulator research yard

9 Design and typical measured electron beam parameters Parameter symbol design measured unit Final linac e energy γmc GeV Bunch charge Q nc Final bunch length (rms) σ zf mm Final peak current pk Ι ka Final slice energy spread (rms) σ Ef /E 0 <0.01? Projected x emittance (linac) γε L x μm Projected y emittance (linac) γε L y μm Single bunch rep. rate f Hz Final rel.. energy jitter (rms) σ Ε /E Final timing jitter (rms) σ t < fs Bunch charge jitter σ Ν /N Hor.. pointing jitter (rms) x 2 1/2 /σ x Peak current jitter σ Ι /I < nc and 1 nc beams also measured, but typically with larger emittancee

10 Parameter Electron energy Single bunch rep. rate Norm. rms emittance Peak current Slice energy spread (rms) Mean undulator beta function Photon energy FEL power gain length FEL fundamental power Rel.. FEL bandwidth (FWHM) Photon pulse duration (FWHM) Energy per pulse Number of photons/0.1-bw Peak brightness (0.1-BW/s/mm 2 /mmrad 2 ) Average brightness (at 30 Hz) Relative power in 3 rd harmonic Relative power in 5 th harmonic Estimated 2009 FEL Performance symbol E 0 f γε x,y I pk σ E /E 0 β x,y hω Lg P FEL Δω/ω Δτ E FEL N γ B pk B avg P 3 /P 1 P 5 /P 1 15 Å FEL (?) ~ 1 ~ Å FEL (?) ~ 1 ~ 0.1 units GeV Hz μm ka m kev m GW fs mj

11 Laser Spatial and Temporal Shaping R = 1.4 mm ps 7.2 ps Spatial shape on cathode using iris 99 Drive Laser up time! Temporal shape (6.6 ps FWHM) S. Gilevich, G. Hays, P. Hering, A. Miahnahri, W. White

12 Transverse Electron Jitter (position & angle) 1-σ beam size Q = 0.25 nc Normalized phase space centroid jitter after BC1 (~4 of rms beam size) RMS A xn = 3.9 RMS A yn = 3.4 Stability is not so far off of our goals (~10) D. Ratner near end of linac (~12 of rms beam size, but sometimes larger) RMS A xn = 14 RMS A yn = 9 Thanks to Controls group for new BPM electronics! ΔE/E jitter 0.03 ΔQ/Q jitter 1.5

13 Bunch Compression Measured after BC2 (0.25 nc) Bunch length after BC2 measured with transverse RF σ z < 10 μm resolution limit σ z 10 μm old screen used poor res. σ z > 25 μm 2º shift applied to simulation L2 BC2 (4.3 GeV) TCAV (5.0 GeV) 550 m BSY (14 GeV)

14 Emittance Near End of Linac Over Long Weekend γ(ε x ε y ) 1/2 = 1.04 μm weekend run at 0.25 nc, with no tuning Saturates at 1.5 Å in 100 m (assuming BBA, etc) (3.3 days) May 24, :01 to May 27 09:00

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

16 LCLS Installation and Commissioning Time-Line PEP-II run ends now LTU/Und/Dump Install PPS Cert. LTU/Dump FEE/NEH Install Und. Seg. Install First Light in FEE X-Rays in NEH FEH Hutch BO FEH Install First Light in FEH CD-4 (7/31/2010) JJ F M A M J J A S ON D J F M AM A M J J A S O N D J F M A M J J 2008 Down PPS Linac/BC2 Commissioning Re-commission Inj/BC2 to SL2 LTU/Und Comm. FEE Comm. NEH Operations/ Commissioning May 2, 2008

17 LTU/Undulator/FEE/FEL Commissioning H. Tompkins