Update on awake synchronization with sps
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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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Update on awake synchronization with sps

Update on AWAKE synchronization with SPS

Andy Butterworth (BE/RF)

Wolfgang Hofle, Thomas Bohl (BE/RF)



  • Requirements and constraints

  • Laser mode locker frequency

  • Synchronization procedure

  • Proposals for frequency generation and signal transmission

  • Conclusions



  • 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)



proton bunch (1s~300ps)

laser pulse (30fs)



  • 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




Frequency constraints

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)

Mode locker f requency choice

Mode locker frequency choice

“Common frequency” used for synchronization

Mode locker frequency

e- gun frequency


e- gun frequency


to get SPS RF frequency reference

SPS RF frequency reference

1 pulse every 5 SPS turns

Thomas Bohl

Synchronization procedure 1

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.

Synchronization procedure 2

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:




Magnetic field

(beam energy)

Synchronization signals

Synchronization signals


RF reference frequency (+/- 1 kHz)

1 pulse every 5 SPS turns

laser pulse picker

10Mhz reference for synchronization of instrumentation etc.

Proposal 1

Proposal 1


Frequency generation provide by Amplitude

Stabilized fibre links developed by CERN BE/RF

Proposal 2

Proposal 2


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



  • 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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