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Multi-Bunch Options for LCLS

Multi-Bunch Options for LCLS. Ability for changes during RF pulse Franz-Josef Decker 19-Oct-2001. From previous talks:. Multi-Bunch Operation for LCLS March 17, 2010 Two-Bunch Test with LCLS Lasing July 29, 2010

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Multi-Bunch Options for LCLS

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  1. Multi-Bunch Options for LCLS Ability for changes during RF pulse Franz-Josef Decker 19-Oct-2001

  2. From previous talks: • Multi-Bunch Operation for LCLS March 17, 2010 • Two-Bunch Test with LCLS Lasing July 29, 2010 • Multi-Bunches for the LCLS April 18, 2011 • all at: V:\AD\Drop Boxes\Decker\Drop\LCLS

  3. What Can the Accelerator Do? • Bunches with the same parameters: • Charge, energy, bunch length, … • Spacing from 0.35 ns (RF) to 400 ns • Bunches with different parameters: • Difference is dependant on bunch spacing: • Energy change: E  10 MeV/ns • Peak current:  80 A/ns • Bunches can have different charge: 250 pC + 20pC

  4. SLAC LINAC Experience with Multi-Bunch Operations • SLC: 3 bunches, 60 ns apart, 7000 pC • E158: 1000 bunches, 350 ns long, 100 pC • E155: 1400 bunches, 500 ns long, 0.3 pC 15% energy variation  0.1% • LCLS multi-bunch range: 2-50 bunches, 0.35 – 400 ns, 20-500 pC Energy spread Energy

  5. Accelerator Issues for LCLS • Two drive lasers at gun • allow variable time delays, 4*150 pC or 8*80 pC or 16*40 pC • Accelerating field varies over 400 ns pulse • affects energy, compression, beam trajectory • Bunches affect each other • wakefields: energy, compression, beam trajectory • Diagnostics not fast enough yet • Individual control of bunches not trivial • some experience at SLAC • Dump power limit (5 kW): 12 bunches, 250 pCeach

  6. LCLS Multi-Bunch Correction Schemes • Energy compensating was done sector by sector (100m) • one low-energy sector compensated four high-energy sectors, this non-local correction causes different beam trajectories • Fast kickers required at undulator entrance • Special RF sections Gun, L0, L1S, L1X need waveform modifications • L2 needs fast phase control to adjust compression Normal Energy Gain Curve Maximum variation 400 ns

  7. RF Phase Manipulation • SLC 1990: 6.8 in 60 ns in NRTL LCLS 2009: 4.0 difference between over- and under-compression in L2 with SLED: 1/2 at input (1/3 at output) and 800ns fill time (600 ns NRTL): we need about 100 ns for 4 change

  8. Tools we used • SLED RF timing and 180 for energy change: • PSK2_L2 and PSK2_L3 for Two-Bunch Test (LCLS) • Additional PSK pulse(s) 180(“SLEDF “ triggers for E-155) • +/- 90  for phase change: • 90 ”Judkin box” for NRTL compressor (SLC) now at CID (?)

  9. Tools we need • L3: E (PSK2_L3) on-off-time, need 180 for more change • L3: phase not necessary • L2: E (PSK2_L2) on-off-time is enough to keep BC2 E • L2: phase is necessary: 90 to change chirp • L1: L1S and/or L1X control is there (I/Q waveform), but changing the waveform files is lengthy (no easy knob) not SLEDed (there was a small difference after BC1) • Gun, L0A, L0B same with waveforms • Fast kickers required at undulator entrance 500V to strip-line • Two injector lasers and/or split and delay

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