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Update on AWAKE synchronization with SPS

Update on AWAKE synchronization with SPS. Andy Butterworth ( BE/RF) Wolfgang Hofle, Thomas Bohl ( BE/RF ). Outline. Requirements and constraints Laser m ode locker frequency Synchronization procedure Proposals for frequency generation and signal transmission Conclusions.

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Update on AWAKE synchronization with SPS

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  1. Update on AWAKE synchronization with SPS Andy Butterworth (BE/RF) Wolfgang Hofle, Thomas Bohl (BE/RF)

  2. Outline • Requirements and constraints • Laser mode locker frequency • Synchronization procedure • Proposals for frequency generation and signal transmission • Conclusions

  3. Requirements • Synchronization between e- gun and laser: few hundred femtoseconds • cf. the plasma period (~ 4 ps) • required for deterministic injection of the witness electron bunch into the plasma wakefields. • Achieved by driving the RF gun with a laser pulse derived from same laser system as used for ionization. • Synchronization between proton beam and laser: < 100ps desirable • cf. proton bunch length (  300ps) Electron bunch (1s ~5ps) Plasma gas proton bunch (1s~300ps) laser pulse (30fs)

  4. Requirements • SPS RF situated in Point 3 next to CCC • Low-level RF electronics in Faraday Cage in BA3 surface building • Synchronization signals to be exchanged on fibres between AWAKE and BA3 • drift/jitter in ps range BA3 ~3km AWAKE

  5. Frequency constraints • Laser requires stable mode-lock frequency reference • between about 50 and 100 MHz • it cannot follow the changes in SPS frequency through the acceleration cycle • SPS and AWAKE cannot be permanently locked together in frequency • SPS must synchronize to AWAKE reference just before extraction of the p+ beam • e- RF gun has limited bandwidth: 2998.5 +/- 1 MHz • and must be locked to the laser frequency (frequency multiple) • SPS RF frequency at extraction = 200.394 +/- 0.001 MHz • adjustment limited by radial beam position • Relationships between frequencies should be feasible to generate in hardware (fairly small integer division/multiplication ratios)

  6. Mode locker frequency choice “Common frequency” used for synchronization Mode locker frequency e- gun frequency multiplier e- gun frequency division/multiplication to get SPS RF frequency reference SPS RF frequency reference 1 pulse every 5 SPS turns Thomas Bohl

  7. Synchronization procedure (1) 1. Rephasing: • Reference signals from AWAKE required by SPS for rephasing: • “Common frequency” fc=frev SPS/5 jitter << 1 SPS RF period (5 ns) • RF frequency reference: 200.394 +/- 0.001 MHz jitter << 10 ps natural beam motion • “Coarse” rephasing: • use the common frequency as a reference. • by manipulating the SPS RF frequency, align the SPS beam with the fc pulse. • precision < 1 SPS RF period (~2 ns) • “Fine” rephasing: • lock the SPS RF frequency to the AWAKE reference RF frequency with a phase-locked loop • precision to O(10 ps) ? 2. Extraction timing: • 1 proton bunch every ~30 seconds: extract beam to coincide with the laser pulse • extraction takes place at variable time in cycle • needed in order to synchronize with the laser pulse: • frep laser pulse repetition frequency (~10 Hz) jitter << 12 ns laser rep.

  8. Synchronization procedure (2) • Start flat-top, launch rephasing, wait 500msfor rephasing to be finished • Wait for next frep pulse, arm counters etc. for next pulse • Next frep pulse sends external event to central timing (for extraction forewarnings) and starts fine timing for bunch rotation and extraction SPS cycle: Injection Ramp Flat-top Magnetic field (beam energy)

  9. Synchronization signals CERN BE/RF RF reference frequency (+/- 1 kHz) 1 pulse every 5 SPS turns laser pulse picker 10Mhz reference for synchronization of instrumentation etc.

  10. Proposal 1 CERN BE/RF Frequency generation provide by Amplitude Stabilized fibre links developed by CERN BE/RF

  11. Proposal 2 CERN BE/RF Fibre link Stabilized fibre link provided by Menlo Transport only 88 MHz (+ 10 Hz modulation?) Frequency generation done on SPS side, developed by CERN BE/RF

  12. Conclusions • A scheme for SPS synchronisation with AWAKE has been developed • similar to technique used for filling LHC • synchronization signals have been specified • timing scheme for synchronization and extraction has been proposed • The laser mode locker frequency has been chosen and included in the specifications given to the laser supplier • Key components are under discussion with manufacturers: • frequency generation chain to synchronize laser, RF gun and SPS RF • fibre signal transmission between SPS P4 and SPS RF

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