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LCLS

Linac/BC2 Commissioning (Dec. 2007 through Sep., 2008) J. Frisch, et al. LCLS FAC Meeting Oct. 30, 2007. LCLS. http://www-ssrl.slac.stanford.edu/lcls/internals/commissioning/index.html. Commission in Jan. 2008. Injector Commissioning. LCLS Accelerator Schematic. 250 MeV  z  0.19 mm

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LCLS

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  1. Linac/BC2 Commissioning(Dec. 2007 through Sep., 2008)J. Frisch, et al.LCLS FAC MeetingOct. 30, 2007 LCLS http://www-ssrl.slac.stanford.edu/lcls/internals/commissioning/index.html

  2. Commission in Jan. 2008 Injector Commissioning LCLS Accelerator Schematic 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 DL1 L 12 m R56 0 DL2 L =275 m R56  0 SLAC linac tunnel research yard

  3. BC2/Linac Commissioning Goals No problems expected Expect we can run at 1nC No specific problems expected – but lots to do No problems expected This is the tricky one No known issues, but there could be surprises

  4. LCLS BC2-Area Layout OTR screens (3) Dipole magnets (4) Kicker magnet (1) Transverse RF deflector (1) S-band RF acc. sections 4 wire-scanners “de-scoped” 4 wire-scanners in sec-28 (300 m downstream) Can measure gex,y here, with BC2 OFF OTR21 BXKIK TCAV3 (25-2d) OTR22 (25-3d) OTR_TCAV (25-9) BC2 4.3 GeV (not to scale)

  5. Linac/BC2 Commissioning Scope • New 4-dipole chicane in 24-7 – 24-8 • Adjacent matching quads and new optics • 3 new OTR screens, 1 collimator, 1 BPM, and 2 moved wire-scanners in sec-28 (4 wires in sec-24 are “de-scoped”) • Transverse RF deflector at 25-2d + x-kicker 25-3d • Two new coherent radiation-based bunch length monitors • Energy and bunch length feedback loop and new SS sub-boosters in 24-1,2,3 + 24-8 (TCAV3) • No new linac BPM electronics in 2008 (or ’09?)

  6. Manpower and Scheduling • Ten months of commissioning BC2/Linac (Dec - Sep) • More help with commissioning shifts (H.-D. Nuhn, F.-J. Decker, Z. Huang, Y. Ding, D. Ratner) • Did 3 shifts per week for 5 months in 2007 - exhausting • No weekend shifts (ops only) after 1st month of startup • Operators now somewhat experienced on injector • Need two physicists/shift for 10 shifts/week (after 1st month) • Need to cover 20 man-shifts/week - have at least 14 physicists – requires a total of 1.5 shifts/week/man (after 1st month) • Shutdown LCLS for 2 weeks in March? (new gun probes + fix GTL)

  7. Last Run’s Typical Shift Schedule

  8. Schedule linac/BC2 Install LTU/Und/Dump FEE/NEH Install X-Ray tunnel/FEH Install 1st FEL Light Now 1st Spont. Light 1st Users J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D PPS 2007 2008 2009 PPS FEL Commissioning Controls checkout & re-commission injector Re-commission Inj/BC2 to SL2 downtime …Injector Commissioning Linac/BC2 Commissioning LTU/Und/FEE Commissioning commissioning time

  9. BC2 Commissioning Parameters May 12, 2007

  10. BC2 Layout Two new OTR screens + LOLA & kicker

  11. BC2 Layout OTR screen Collimator BPM • 23-m long chicane • Translates horizontally up to 52 cm

  12. New construction in BC2 (sector 24/25) Oct. 11, 2007

  13. New construction in BC2 (sector 24/25) Oct 26

  14. New Pre-Beam Tunnel Check List 17 pages Polarity conventions Installation orientation Component bar codes etc. etc.

  15. Magnet Power Supply Modifications • Only QUAD’s 24201-24501 (4 of original 8) remain on sector-24 bulk supply (keep 0-20 A boost for each) • Q24601 gets its own supply • Doubled-up Q24701A/B gets its own supply • Q24801 quad goes away forever (boost supply is free) • Doubled-up Q24901A/B gets its own supply • New QM21 & QM22 (46-cm FFTB quads) each get own supply • Two new MCOR6 tweaker quads (h-correction) as in BC1 • No new correctors here, but all of sectors 20-30 get new MCOR6 corrector supplies to replace old SCOR6 supplies • Control divided between EPICS and SLC • Have software to communicate between systems, but adds complexity. • Still details to work out for LEM, etc .

  16. BC2 Dipole Field Quality OK No quad field and sextupole is just below tolerance

  17. Diagnostics Issues • Can’t tune on something you can’t measure • Engineering issues with the wire scanners • Vibration limits us to slow scan speeds • Can be fixed – but no sure solution in hand • Physics issues with the OTR screens • Coherent effects distort image • May be able to fix with short wavelength filter, but not known.

  18. Wire Scanners Measured beam size Vs. Motor Steps / second Range is 40-140 microns With slow scanning, size was reproducible to 5 microns. May be able to fix problem by adding a gear reducer to wires scanner (cheap), but not tested yet. For now, limited to slow scans 1 minute / scan, 10 minutes for emittance measurement.

  19. Even “ideal” wire scanner only gives integrated profiles Pathological beam shape that would Not be apparent on wires

  20. Coherent Effects in OTRs OTR12 sum signal as QB is varied. BC1 off, L1X, L1S on crest. Y beam size Varies with observed intensity Not clear if effect will be worse after BC2.

  21. OTRs - Plans • Installing diffraction gratings in front of OTR cameras • Hope to find that coherence is only in long wavelength signals • If signal is incoherent below ~400nm can easily add filters to cameras • Installing UV (200nm) and IR (2.5um) detectors on OTRs • IR detectors to understand coherence (not seen yet at DESY / FLASH or Spring-8 / SCCS) • UV detectors to look for coherence at hard UV • If no coherence at 200nm, can use UV cameras (but $$) • Can not show from beam parameters that we don’t have coherence as short at 100nm – beyond the range of conventional cameras. • In future “Laser Heater” will probably fix this problem – but would like to be able to diagnose beam without heater.

  22. Diagnostics – BPMs • Existing linac BPMs have 30 – 100 micron resolution depending on beam charge (300pc – 1nC). • Readout is through SLC – EPICS communication – slow ~5 seconds. • Will need good linac orbit tuning algorithms. • Work underway. • Need initial accuracy ~1mm. OK • Then tune on emittance – should work but slow. • May wish to tune at high charge (~1nC) • Increase effect of wakefields • Better BPM resolution

  23. Diagnostics – where are we? • Wire scanners work but: • For now, just slow scans – hope for a mechanical fix soon • First wires located in S28, 300 meters downstream of BC2 • OTRs • So far can not be used for quantitative measurements • Some plans that may fix the problem, but not clear a solution exists • Discussed at 3-way collaboration meeting at Spring-8 this month. Work underway at other labs. • BPMs • Using old LINAC BPMs. • Should be OK, but readout slow • Next year (?) replace with epics BPMs.

  24. Emittance Preservation and Measurement • Measure emittance after L2: • In BC2 (with compressor straight) using OTR • If we do not have coherent effects – otherwise: • Wire scanner in Sector 28 (300M downstream) • Orbit Tuning • Minimize orbit on Linac BPMS • Then Tune orbit on emittance • In OTR21, or in S28 wires • Might be slow to converge • Then optimize BC2 emittance • This is probably our most serious technical challenge.

  25. Bunch Length measurement • In much better shape than transverse measurements • TCAV in S24 will let us resolve bunch length. • Old cavity in new installation. • No problems anticipated. • Cross check with direct compression measurement using phase cavities • Demonstrated in injector • On line mm-wave bunch length monitors similar to injector monitors • Shorter mm wavelengths, but should work • Unique beam conditions – can always have surprises!

  26. Other Issues • LINAC controls split between EPICS and SLC systems. • We have tools in place to make this work, but could be slow to get going • Limited LINAC tunnel access – B-factory running. • Limited time to make changes or repairs • Systems designed for “Production”, not R+D. • Compact, reliable, and high performance, but difficult ot modify.

  27. Additional Run Plans • Improve performance of injector • Better BC1 magnet field quality • X-band cavity moved to reduce steering • Try programmable phase ramp in L0A to reduce bunch length / improve emittance • New RF system for phase stabilization over ~1km beamline • New temperature stabilized transmission lines • Need to compare with beam timing and MDL. • Complexities due to path length changes in bunch compressors. • Commission new beam feedbacks • Energy and bunch length throughout machine • Energy at 3 points, bunch length at 2, beam time. • Transverse feedbacks throughout machine • Optimize orbit on emittance, then stabilize

  28. Summary • Linac/BC2 e- commissioning starts in early Dec. ’07 • Large amount of commissioning time available (fewer shifts/week & no weekends after 1st month?) • Main ’07 goal is to verifyfull functionality of linac/BC2 beamline, plus diagnostics and controls • Optimizing performance may take longer • Will need some linac access in first 1-2 months

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