Update on AWAKE synchronization with SPS

Andy Butterworth (BE/RF)Wolfgang Hofle, Thomas Bohl (BE/RF)

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

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)

laser pulse (30fs)proton bunch (1 ~300ps)

gasPlasmaElectron bunch (1 ~5ps)

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

AWAKE

~3km

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 frequency choice

“Common frequency” used for synchronization

Mode locker frequency

e- gun frequencymultiplier

e- gun frequency

division/multiplicationto get SPS RF frequency reference

SPS RF frequency reference

Thomas Bohl

1 pulse every 5 SPS turns

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)• Start flat-top, launch rephasing, wait 500ms for 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)

Synchronization signals

CERN BE/RF

1 pulse every 5 SPS turns

RF reference frequency (+/- 1 kHz)

laser pulse picker

10Mhz reference for synchronization of instrumentation etc.

Proposal 1

CERN BE/RF

Frequency generation provide by AmplitudeStabilized fibre links developed by CERN BE/RF

Proposal 2

CERN BE/RF

Stabilized fibre link provided by MenloTransport only 88 MHz (+ 10 Hz modulation?)Frequency generation done on SPS side, developed by CERN BE/RF

Fibre link

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