1. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 1 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

2. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 2 LCLS Accelerator Schematic SLAC linac tunnel research yard Linac-0 L =6 m Linac-1 L  9 m  rf   25° Linac-2 L  330 m  rf   41° Linac-3 L  550 m  rf  0° BC1 L  6 m R 56   39 mm BC2 L  22 m R 56   25 mm DL2 L =275 m R 56  0 DL1 L  12 m R 56  0 undulator L =130 m 6 MeV  z  0.83 mm    0.05 % 135 MeV  z  0.83 mm    0.10 % 250 MeV  z  0.19 mm    1.6 % 4.30 GeV  z  0.022 mm    0.71 % 13.6 GeV  z  0.022 mm    0.01 % Linac-X L =0.6 m  rf =  21-1 b,c,d...existing linac L0-a,b rfgun 21-3b24-6d X 25-1a30-8c Injector Commissioning Commission in Jan. 2008

3. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 3 BC2/Linac Commissioning Goals This is the tricky one No problems expected Expect we can run at 1nC No specific problems expected – but lots to do No problems expected No known issues, but there could be surprises

4. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 4 OTR screens (3) Dipole magnets (4) S-band RF acc. sections LCLS BC2-Area Layout 4.3 GeV (not to scale) BC2 OTR21 OTR22(25-3d) OTR_TCAV(25-9) BXKIK Kicker magnet (1) TCAV3(25-2d) 4 wire-scanners “de-scoped” Transverse RF deflector (1) 4 wire-scanners in sec-28 (300 m downstream) Can measure  x,y here, with BC2 OFF

5. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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 1 st month of startup Operators now somewhat experienced on injector Need two physicists/shift for 10 shifts/week (after 1 st month) Need to cover 20 man-shifts/week - have at least 14 physicists – requires a total of 1.5 shifts/week/man (after 1 st month) Shutdown LCLS for 2 weeks in March? (new gun probes + fix GTL)

7. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 7 Last Run’s Typical Shift Schedule

8. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 8 Schedule JASONDJFMAMJJASONDJFMAMJJ linac/BC2 Install Linac/BC2 Commissioning LTU/Und/Dump FEE/NEH Install 20072008 LTU/Und/FEE Commissioning ASOND 2009 PPS Controls checkout & re-commission injector Re-commission Inj/BC2 to SL2 X-Ray tunnel/FEH Install FEL Commissioning …InjectorCommissioning Now PPS 1st Spont. Light 1st FEL Light 1st Users downtime commissioning time

9. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 9 BC2 Commissioning Parameters ParameterValueComments RF rate 30 Hz May test 120Hz Beam rate ≤30 Hz 10 Hz e  beam as baseline – short term 30-Hz tests (beyond 30 Hz is unnecessary) Drive-laser rate 30 Hz Possible 120-Hz late in the run? Bunch charge 250 pC Start at this low charge but later up to 1-nC Drive-laser pulse length ~6 ps fwhm Optimum not clear yet Final beam energy 13.6 GeV 13.6 GeV typically with tests down to 4.3 GeV May 12, 2007

10. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 10 BC2 Layout Two new OTR screens + LOLA & kicker

11. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 11 BC2 Layout BPM Collimator OTR screen 23-m long chicane Translates horizontally up to 52 cm

12. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 12 New construction in BC2 (sector 24/25) Oct. 11, 2007

13. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 13 New construction in BC2 (sector 24/25) Oct 26

14. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 14 New Pre-Beam Tunnel Check List 17 pages etc. etc. Component bar codes Polarity conventions Installation orientation

15. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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 (  -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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 16 BC2 Dipole Field Quality OK No quad field and sextupole is just below tolerance

17. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 19 Even “ideal” wire scanner only gives integrated profiles Pathological beam shape that would Not be apparent on wires

20. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 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. Joe Frisch LCLS FAC Frisch@SLAC.Stanford.edu Oct. 30, 2007 28 Summary Linac/BC2 e  commissioning starts in early Dec. ’07 Large amount of commissioning time available (fewer shifts/week & no weekends after 1 st month?) Main ’07 goal is to verify full functionality of linac/BC2 beamline, plus diagnostics and controls Optimizing performance may take longer Will need some linac access in first 1-2 months