1. 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

2. 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

3. 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

4. Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep =88.173502 MHz 1550 nm DET10A 780 nm (doubler) Laser head 88. 173 MHz from external ThorLabs photo diode BLP-903 dB AM-1431 6 dB DCB NLP-100 90 MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source analyser (SSA) Laser system without additional MenloSystems synchronization

5. 88 MHz from DET10A photo diode Power to SSARemarks10 Hz to 10 MHz jitter 1.-0.6 dBmLaser unlocked4.8 ps (dominated by 1-10 Hz)  Total jitter in given frequency range: Noise floor of measurement set-up 88.173 MHz Phase noise density spectrum Jitter Drift 10 Hz Plot normalized to carrier amplitude Frequency rangeJitter [fs] 1 Hz – 10 Hz (drift)4798 10 Hz – 100 Hz373 100 Hz – 1 kHz112 1 kHz – 10 kHz49 10 kHz – 100 kHz51 100 kHz – 1 MHz146 1 MHz – 10 MHz466 10 Hz to 1 MHz: 0.4 ps Jitter: ‘area below curve’

6. Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep =88.173502 MHz 1550 nm DET10A 780 nm (doubler) Laser head 88. 173 MHz from external ThorLabs photo diode BLP-903 dB AM-1431 6 dB DCB NLP-100 90 MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source analyser (SSA) Laser system without additional MenloSystems synchronization

7. Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep =88.173502 MHz 1550 nm DET10A 780 nm (doubler) Laser system with additional MenloSystems synchronization Laser head 88. 173 MHz from external ThorLabs photo diode BLP-903 dB AM-1431 6 dB DCB NLP-100 90 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:

8. 88 MHz from DET10A photo diode Power to SSARemarks1 Hz to 10 MHz10 Hz to 1 MHz 1.-0.6 dBmLaser unlocked4.8 ps0.42 ps 2.-0.7 dBmInitial PID settings0.53 ps0.21 ps 3.-0.9 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? 88.173 MHz

9. Photo diode at 3 GHz (in-loop, locked) “Fiber Ring Oscillator” (Comb) F rep =88.173502 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

10. Comparison 88 MHz/3 GHz (locked) Power to SSARemarks1 Hz to 10 MHz jitter 1.-2.2 dBm3 GHz0.56 ps (dominated by 10-100 Hz) 3.-0.9 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 10 34 = 30.6 db Unphysical noise floor due to scaling (scaled to) 3 GHz

11. Conclusions from measurements 1.Laser must be locked to external reference 2.Mode locker frequency 88.173502 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 = 2.998 GHz (or very close)

12. New draft layout, laser part “Fiber Ring Oscillator” (Comb) F rep =88.173502 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 88.173502 MHz (laser) 2997.8991 MHz (laser) 2997.8991 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

13. New draft layout, RF signals part 88.173502 MHz (laser) 2997.8991 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  2.998 GHz from reference master for all RF signals 2 1 17 1 10164 1 870 1 Reset logic f rep 9.97 Hz Frac. div.  25/11 f c 8.68 kHz 88.173502 MHz (laser synchronous) f RF, SPS 200.394 MHz VME trigger unit Laser trigger prepulse f rep Warning AWAKE Beam with 2 nd f rep 1498.9495 MHz 2997.8991 MHz electron beam Synchronization (CTRV)

14. Distributed frequencies (from laser room) SignalFrequencyComment 1AWAKE 10 MHz GPS ref.10 MHzAbsolute GPS reference 2RF reference e-beam, f eRF 2997.899068 MHzSynthesized from 10 MHz 3Mode locker frequency, f ML 88.173502 MHzf ML = f eRF /34 4RF reference e-beam/2, f eRF /21498.949534 MHzFast bucket counters 5200 MHz RF SPS200.3943227 MHzf ML · 25/11 for RF synchronization 6Common frequency, f c 8.675078906 kHzf ML · 25/(11 · 5 · 4620) = f ML /10164 7Laser repetition rate, f rep 9.971355064 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

15. 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

16. Spare slides

17. 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

18. 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

19. 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 ?

20. Measurements at MPP “Fiber Ring Oscillator” (Comb) F rep =88.173502 MHz 1550 nm PD 780 nm (doubler) Piezo control, not connected Laser system as delivered commissioned at MPP measurement (“free running”) Laser head 88. 173 MHz from internal photo diode BLP-9010 dB AM-1431 6 dB DCB NLP-100 90 MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source analyser (SSA)

21. 88 MHz output of laser head Power to SSARemarks1 Hz to 10 MHz jitter 1.0.1 dBmReference case15 ps (12 ps) 2.-10.0 dBmAdditional 10 dB before SSA15 ps (12 ps) 3.-8.1 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 88.173 MHz

22. 88 MHz from E8663B generator Power to SSARemarks1 Hz to 10 MHz jitter 1.0.9 dBmReference case0.76 ps 2.-11.0 dBmAdditional 10 dB before SSA0.77 ps 3.-10.9 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 88.173 MHz

23. 88 MHz from DET10A (locked) Power to SSARemarks1 Hz to 10 MHz jitter 1.-0.9 dBmFinal PID settings0.55 ps (dominated by 1-10 MHz) 2.-11.6 dBm10 dB after photo diode1.7 ps (increased noise floor) 3.-11.2 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! 88.173 MHz

24. Comparison with E8663B (3 GHz) Power to SSARemarks1 Hz to 10 MHz jitter 1.-2.2 dBmDSC50S diode, locked0.56 ps (dominated by 10-100 Hz) 2.5.4 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

25. Passive open loop measurement “Fiber Ring Oscillator” (Comb) F rep =88.173502 MHz 1550 nm DET10A 780 nm (doubler) Laser head 88. 173 MHz from external ThorLabs photo diode BLP-902 dBDCB NLP-100 90 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

26. 88 MHz from DET10A (passive) Power to SSARemarks1 Hz to 10 MHz jitter 1.-8.3 dBmReference15 ps 2.-15.7 dBm10 dB after photo diode8.6 ps (photo diode current?) 3.-18.3 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? 88.173 MHz from photo diode 88.173 MHz from E8663 generator