Measurements with laser at MPP and updates on RF synchronization Reported by Heiko Damerau (CERN) Measurements jointly with J. Moody, P. Muggli (MPP), K. Hartinger (Menlo Systems), W. Hofle (CERN) Acknowledgements: T. Bohl, A. Butterworth, S. Doebert, J. Molendijk, S. Rey (CERN) 12 February 2015

Overview Introduction Measurements with laser at MPP 88 MHz from photo diode (780 nm) 3 GHz from wide-band photo diode (1550 nm) Updated layout Laser phase locked loop RF signals and beam synchronous pulses Summary

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. MASTER 3 GHz LLRF Clock Generation Fiber Optic link (FO) based on T. Bohl, A. Butterworth, W. Hofle Sufficient quality to lock laser and to generate RF at 3 GHz for e-beam? AWAKE Technical Board December 2014

Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep = MHz 1550 nm DET10A 780 nm (doubler) Laser head MHz from external ThorLabs photo diode BLP-903 dB AM dB DCB NLP MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source analyser (SSA) Laser system without additional MenloSystems synchronization

88 MHz from DET10A photo diode Power to SSARemarks10 Hz to 10 MHz jitter dBmLaser unlocked4.8 ps (dominated by 1-10 Hz)  Total jitter in given frequency range: Noise floor of measurement set-up MHz Phase noise density spectrum Jitter Drift 10 Hz Plot normalized to carrier amplitude Frequency rangeJitter [fs] 1 Hz – 10 Hz (drift) Hz – 100 Hz Hz – 1 kHz112 1 kHz – 10 kHz49 10 kHz – 100 kHz kHz – 1 MHz146 1 MHz – 10 MHz Hz to 1 MHz: 0.4 ps Jitter: ‘area below curve’

Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep = MHz 1550 nm DET10A 780 nm (doubler) Laser head MHz from external ThorLabs photo diode BLP-903 dB AM dB DCB NLP MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source analyser (SSA) Laser system without additional MenloSystems synchronization

Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep = MHz 1550 nm DET10A 780 nm (doubler) Laser system with additional MenloSystems synchronization Laser head MHz from external ThorLabs photo diode BLP-903 dB AM dB DCB NLP MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source analyser (SSA) DSC50S PD 10 GHz 3 GHz filter LNA- 6G MenloSystems analog FB (PID) control box E8663B RF generator, 3 GHz Piezo drive MASTER:

88 MHz from DET10A photo diode Power to SSARemarks1 Hz to 10 MHz10 Hz to 1 MHz dBmLaser unlocked4.8 ps0.42 ps dBmInitial PID settings0.53 ps0.21 ps dBmFinal PID settings0.55 ps0.21 ps  Low frequency phase noise lowered by more than ~30 dB when locked  Quick measurement (½ day); 10 kHz bandwidth expected with better adjustment Noise floor of measurement set-up Spurious modulation on signals from laser system, source? MHz

Photo diode at 3 GHz (in-loop, locked) “Fiber Ring Oscillator” (Comb) F rep = MHz 1550 nm 780 nm (doubler) Laser head 3 GHz amplified in-loop signal from 10 GHz photo diode (via 3 dB splitter) DCB DC Block Signal source analyser (SSA) DSC50S PD 10 GHz 3 GHz filter LNA- 6G MenloSystems analog FB (PID) control box E8663B RF generator, 3 GHz Piezo drive MASTER:  Phase detection at 3 GHz is 34 times more sensitive than at 88 MHz

Comparison 88 MHz/3 GHz (locked) Power to SSARemarks1 Hz to 10 MHz jitter dBm3 GHz0.56 ps (dominated by Hz) dBm88 MHz scaled to 3 GHz0.55 ps (dominated by 1-10 MHz) Low frequency noise consistent with expected factor from frequency ratio 34 Shifted servo bump due to 3 dB loop gain difference  Requires better optimized PID settings Shift 88 MHz measurement by 20 log = 30.6 db Unphysical noise floor due to scaling (scaled to) 3 GHz

Conclusions from measurements 1.Laser must be locked to external reference 2.Mode locker frequency MHz would be unfavorable for laser phase locked loop  Harmonic around 3 GHz preferred  Requires reference signal at that frequency 3.RF signal generation  Frequency division easier than multiplication  All RF signals derived from master oscillator at 34 · f ML = GHz (or very close)

New draft layout, laser part “Fiber Ring Oscillator” (Comb) F rep = MHz 1550 nm 780 nm (doubler) Laser head PD 10 GHz 3 GHz filter LPNA MenloSystems analog FB (PID) control box Piezo drive 3 GHz low phase noise GPS 10 MHz PD 10 GHz 3 GHz filter LPNA  Photo diode 88 MHz filter LPNA MHz (laser) MHz (laser) MHz (reference) 10 MHz AWAKE  Preferred baseline: laser phase locked loop based on commercial elements  Check if performance sufficient; intermediate frequency needed? LPNA: Low Phase Noise Amplifier

New draft layout, RF signals part MHz (laser) MHz (reference)  Divider for mode locker frequency must be synchronous with laser oscillator  One fractional divider only to generate f RF, SPS, all other ratios integers  GHz from reference master for all RF signals Reset logic f rep 9.97 Hz Frac. div.  25/11 f c 8.68 kHz MHz (laser synchronous) f RF, SPS MHz VME trigger unit Laser trigger prepulse f rep Warning AWAKE Beam with 2 nd f rep MHz MHz electron beam Synchronization (CTRV)

Distributed frequencies (from laser room) SignalFrequencyComment 1AWAKE 10 MHz GPS ref.10 MHzAbsolute GPS reference 2RF reference e-beam, f eRF MHzSynthesized from 10 MHz 3Mode locker frequency, f ML MHzf ML = f eRF /34 4RF reference e-beam/2, f eRF / MHzFast bucket counters 5200 MHz RF SPS MHzf ML · 25/11 for RF synchronization 6Common frequency, f c kHzf ML · 25/(11 · 5 · 4620) = f ML / Laser repetition rate, f rep Hzf ML · 25/(11 · 5 · 4620 · 870) = f c /870 SignalComment 8Start injection AWAKELast f c pulse before extraction + m · 2/f eRF 9Extraction pulseLast f rep pulse before extraction + n · 1/f RF,SPS (local SPS) Also possible (e.g. for laser):Last f rep pulse before extraction + k · 1/f ML a) RF signals from AWAKE: b) Pulses (one per AWAKE cycle): c) Unsynchronized timings provided by BE-CO: Extraction -80 ms, -50 ms, -20 ms

Summary 88 MHz unfavorable for laser phase locked loop and generation of 3 GHz for electron beam 3 GHz oscillator disciplined by GPS becomes master Updated draft topology for RF signals generation and distribution starting from 3 GHz Proposal for RF signals and beam synchronous pulses  Star distribution from laser room Need your needs to refine RF interfaces with equipment  Define cabling requirements

Spare slides

AWAKE Experimental Layout electrons wakefield potential Synchronize a three beam system: SPS proton bunch LASER pulse RF gun and electron acceleration Provide RF clocks to experiment instrumentation Edda Gschwendtner, CERN

CERN CNGS SPS Edda Gschwendtner, CERN18 SPS BA2 SPS BA3 SPS RF SPS BA4 AWAKE RF Fiber links existing RF Fiber links existing RF Fiber links to LHC RF

Edda Gschwendtner, CERN 19 Layout of the AWAKE Experiment LLRF/synchronization (protected from radiation) Klystron drive Clock distribution (subject to future specification) Note: exact locations of electronics subject to integration studies ps trigger for streak camera ! Power supply UPS ?

Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep = MHz 1550 nm PD 780 nm (doubler) Piezo control, not connected Laser system as delivered commissioned at MPP measurement (“free running”) Laser head MHz from internal photo diode BLP-9010 dB AM dB DCB NLP MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source analyser (SSA)

88 MHz output of laser head Power to SSARemarks1 Hz to 10 MHz jitter dBmReference case15 ps (12 ps) dBmAdditional 10 dB before SSA15 ps (12 ps) dBm (!)Additional 10 dB before amplifier11 ps Modulation at 9.3 MHz?  Low noise amplifier partly saturated, hence carrier amplitude decreased  Noise artificially increased by 2 dB in cases 1. and 2. Significant spurious MHz

88 MHz from E8663B generator Power to SSARemarks1 Hz to 10 MHz jitter dBmReference case0.76 ps dBmAdditional 10 dB before SSA0.77 ps dBm (!)Additional 10 dB before amplifier1.64 ps  Confirms that phase noise of laser head well above limits of set-up  Wide-band noise level of preamplifier approximately -134 dBc (with attenuators) Noise floor of AM-1431 preamplifier Approx. noise level of laser head MHz

88 MHz from DET10A (locked) Power to SSARemarks1 Hz to 10 MHz jitter dBmFinal PID settings0.55 ps (dominated by 1-10 MHz) dBm10 dB after photo diode1.7 ps (increased noise floor) dBm10 dB after 1 st filter1.6 ps (increased noise floor)  Quality of the measurement above few kHz dominated by preamplifier noise  Wide-band noise level of preamplifier approximately -144 dBc  Jitter from 1 Hz to 10 MHz of 88 MHz signal from DET10A diode well below 1 ps Noise floor of AM-1431 preamplifier! MHz

Comparison with E8663B (3 GHz) Power to SSARemarks1 Hz to 10 MHz jitter dBmDSC50S diode, locked0.56 ps (dominated by Hz) dBmE8663B generator0.13 ps (dominated by 1-10 Hz)  Phase noise of photo diode and generator identical only up to 10 Hz  Increased loop bandwidth with optimized PID parameters? 3 GHz

Passive open loop measurement “Fiber Ring Oscillator” (Comb) F rep = MHz 1550 nm DET10A 780 nm (doubler) Laser head MHz from external ThorLabs photo diode BLP-902 dBDCB NLP MHz low-pass DC Block 100 MHz low-pass Signal source analyser (SSA) Cross-check 88 MHz without limiting (?) low-noise amplifier Piezo control, not connected

88 MHz from DET10A (passive) Power to SSARemarks1 Hz to 10 MHz jitter dBmReference15 ps dBm10 dB after photo diode8.6 ps (photo diode current?) dBm10 db in front of SSA12 ps  Larger phase noise compared to measurements with low-noise amplifier  Influence of photo diode current (due to attenuator DC path) on noise? MHz from photo diode MHz from E8663 generator