2. Phase Drift Compensation with sub-picosecond Precision over an Optical Link of 3 km for the AWAKE Experiment 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 2 D. Barrientos, J. Molendijk Acknowledgments to: T. Bohl, A. Butterworth, H. Damerau, E. Gschwendtner, W. Höfle, T. Levens

3. Outline Motivation About AWAKE SPS AWAKE Synchronisation Fibre link Phase Drift Compensation Drift Measurements Simplified Concept Component Selection & Scheme Calibration Design Details Status & Outlook 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 3

4. Motivation – Cavities vs. Plasma Today’s RF cavity / microwave technology: gradient <100 MV/m LHC: 5 MV/m ILC: 35 MV/m CLIC: 100 MV/m Several tens of kilometres for Future Linear colliders 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 4 Use Plasma as ‘cavity’! Gradients in Plasma up to 1000x higher SLAC experiment: 50 GV/m (e - driver) CLIC 3 TeV  48 km ILC 0.5 TeV  31 km Ez Self modulation instability P+ in a plasma creates a wakefield

5. About AWAKE Advanced Proton Driven Plasma Wakefield Acceleration Experiment High energy Proton beam to drive the wakefield results in a much longer plasma length First Proton driven wakefield experiment worldwide 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 5 AWAKE installed in former CNGS Facility (CERN Neutrinos to Gran Sasso)  CNGS physics program finished in 2012

6. SPS AWAKE Synchronisation SPS beams must be delivered at AWAKE in synchronism with the AWAKE e - RF system and the laser pulse rate. Via 3 km fibre optic links SPS RF (point 3) receives: RF reference frequency (~400 MHz) Common frequency F c between AWAKE RF and SPS RF (f rev SPS / 5 ~ 9 kHz) Laser repetition rate (~10 Hz) At flat top SPS RF executes: «Course» re-phasing (< SPS T RF )using F c «Fine» re-phasing (down to 10 ps) requires RF reference frequency received from AWAKE to be stable within <= 1 ps Extraction pulse generation synchronized with Laser rep-rate This talk concentrates on the most critical the RF reference frequency transmission. 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 6 BA3 AWAKE ~ 3 km

7. Fibre Link Phase Drift Compensation – Drift Measurements A series of measurements were made using our Vector Voltmeter VME module* to evaluate the typical phase drift of a fibre link round trip from the SPS faraday cage to AWAKE and back. Total fibre length = 6288 m Issues both with the temperature recording and the phase detector range caused the data of some periods to be un-exploitable. 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 7 Φ deg T °C t * EDA-02557 using AD8364 (mag) and AD8302 (phase)

8. Fibre Link Phase Drift Compensation – Drift Measurements 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 8 0 80 40 T °C Φ deg T °C

9. Fibre Link Phase Drift Compensation – Simplified Concept 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 9

10. Fibre Link Phase Drift Compensation – Simplified Concept 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 10 Ideal Procedure (stepped delay line with fine delay) Regulate both analogue fine delays of Tdf and Tdr to keep  = 0 Once the fine delay gets close to the limit Insert a course delay step on the concerned delay (outside of SPS cycle) Let the regulation loop restore  = 0

11. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 11 Main Critical Components are: Programmable Delay Lines Fine granular sub ps resolution. Course range 10 ns Part to part reproducibility (tracking) Phase Discriminator Good sensitivity Copper to Optical Interfaces Good availability Common Characteristics Low Jitter (< 1 ps) Using noise immune differential signalling

12. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 12 Programmable Delay Lines Criterion Fine granular sub ps resolution. Part to part reproducibility (tracking) SY100EP196 (MICREL) was retained due to: Analogue fine tune-able 0-30 ps + digital 10 ps steps 10 ns range (10 bit) Typical RMS jitter 0.2 ps (max <1 ps) Linearity +/-10%LSB (~ +/-1ps) > 3GHz rated MC100EP196 (ON Semiconductor) was NOT selected: Typical RMS jitter 3 ps Poor Linearity MICREL®

13. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 13 X-OR Phase Discriminator Good sensitivity -> PECL about 800 mV/180° 640 µV/ps @ 400 MHz X-OR gate MC100EP08 was retained due to: Typical jitter 0.2 ps (max <1 ps) Fully differential LVPECL operation > 3 GHz rated Low cost

14. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 14

15. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 15 Copper to Optical Interface Profit from newer low-cost technologies Previous Experience: LLRF LHC uses older pig-tail TX / RX STX-24-PST-B & SRX-24-PST-B (OCP) SONET OC-24 Max raw Bit-rate 1.3 Gbps Mfgr. Spec. RMS Jitter 0.005 UI = ~3.8 ps Much better with stable clocks vs data! Implement generic SFP cage equipped with for example: Low cost: FTLF1321P1BTL (Finisar) SONET OC-48 λ = 1310 nm (mono-mode fibre) Max raw Bit-rate = 2.67 Gbps Mfgr. Spec. RMS Jitter 0.007 UI = ~2.6 ps Much better with stable clock operation Measured TX+RX 10Hz to 100MHz J SFP ~ 400 fs (Actually only of interest up-to 100kHz)

16. Fibre Link Phase Drift Compensation – X-OR Scheme 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 16 Valid approach if delay controls have perfect delay tracking. Imperfections will cause drift when course stepping one delay line (end of analogue control range) How to calibrate Tdf = Tdr? Or worse Tdf = Tdr + Offset? (when Tff ≠ Tfr small delta) X-OR

17. Fibre Link Phase Drift Compensation – Calibration 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 17 Add one delay line to create 90° phase shift in one branch T 90° Added circuits to enable calibration. 1:4 Fanout Buffer, NB6L14 (3 GHz) 2 x 2 Crossbars, NBSG72A (>7 GHz) Both devices member of the new ON Semiconductor series

18. Fibre Link Phase Drift Compensation – Calibration 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 18 Phase 1: Calibrate T 90° Set T 90° Delay to a reasonable value Connect phase detector to T 90° Delay driven from reference source only Search for E = 0 by varying T 90°

19. Fibre Link Phase Drift Compensation – Calibration 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 19 Phase 2: Equalise Delay lines T df = T dr Connect phase detector to the reference source via T df, T dr & T 90° Search for E = 0 by varying either of Delay lines T df or T dr

20. Fibre Link Phase Drift Compensation – Calibration 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 20 Phase 3: Beam based calibration Using Operational Connections Both phase 1 & 2 introduce small errors due to device output skew (5 ps typ) Additionally we may have Tff ≠ Tfr Add a small delay offset to one Tdf or Tdr delay to remove residual drift.

21. Fibre Link Phase Drift Compensation – Design Details 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 21 Circuits in critical path have separate linear regulated supplies: V CCA (+3.3V source) V TTA (+1.3V sink for LVPECL terminators) Use complementary X-OR outputs representing +E and -E Common references for both ADC driver level shifters ADC drivers optimal dynamic range 2.5V/180° => ~0.019 ps / LSB (16 bit ADC and RF@400MHz) Subtraction of the Digital +E with -E eliminates LVPECL and reference offsets / drifts in both branches LPF out [V]ADC-P [V]ADC-N [V] 2.32.50 1.91.25 1.502.5 LPF AD7903 Dual Diff 16 bit ADC

22. Fibre Link Phase Drift Compensation – Critical Path 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 22 cm

23. Status & Outlook 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 23 The Phase Drift Compensation System design is currently frozen The PCB design layout is being finalized at this moment A dual x 3 km fibre link test system has just been received Cabled proto-types expected by mid December Initial hardware lab tests with the fibre link test system by end 2015 Early 2016 Installation of one system in the AWAKE laser room Later 2016 start of Phase 1 experimental program with SPS beam … Dual 3 km test link setup

24. Thank You for your Attention 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 24

25. Backup Slides 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 25

26. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 26 MC100EP196 limitations are: Random jitter performance 3 ps Non linear analogue fine delay Non monotonic non linear steps ON Semiconductor® D. Valuch CERN BE/RF MC100EP195 step delay measurements using Agilent E5071C on SPS Damper Loops module EDA-02917

27. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 27 Test results FTLF1321P1BTL (Finisar) Signal quality measurement using SSA E5052B Keysight comparing the Phase Noise of: E4428C Agilent (red) Same but through SFP test fixture (green & black) Green VME power- supply Black E3620A HP ext. supply From 10Hz to 100MHz J SFP ~ 400 fs -100 dB -120 dB -140 dB 1Hz1kHz 1MHz

28. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 28 Test results FTLF1321P1BTL (Finisar) Signal quality measurement using SSA E5052B Keysight comparing the Phase Noise of: E4428C Agilent @ 400MHz (background) SFP connected to fibre test system. Transceiver powered by ext. E3620A HP supply From 1Hz to 100kHz J SFP+FF+FR ~ 190 fs 1Hz100Hz 10kHz -120 dB -100 dB -60 dB 10Hz1kHz100kHz Signal quality measurement done through 2 x 3 km fibre test system with an optical splitter midway. -140 dB

29. Fibre Link Phase Drift Compensation – Component Selection 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 29 Signal quality measurement test setup: 2 x 3 km fibre with an optical splitter midway. FTLF1321P1BTL TX RX

30. Fibre Link Phase Drift Compensation – ADC Driver 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 30 U1 + U2 = ADA4941-1 Analog Devices 18 bit ADC Driver

31. AWAKE Experimental Program Phase 1: Understand the physics of self modulation instability processes in plasma. Phase 2: Probe the accelerating wakefields with externally injected electrons. 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 31 laser pulse proton bunch gas plasma Laser dump SPS protons 10m SMI Proton beam dump Laser Proton diagnostics BTV,OTR, CTR p Plasma cell  Rb vapour source Proton beam  drives the plasma wakefield + undergoes self-modulation instability.  LHC-type proton beam, 400 GeV/c, 3E11 protons/bunch,,  = 400 ps long Laser beam:  ionizes the plasma + seeds the self-modulation instability of the proton beam.  4.5 TW laser, 100 fs

32. AWAKE Experimental Program Phase 1: Understand the physics of self modulation instability processes in plasma. Phase 2: Probe the accelerating wakefields with externally injected electrons. 06/11/2015 LLRF15, Phase Drift Compensation with sub-picosecond Precision... 32 Laser dump e-e- SPS protons 10m SMI Acceleration Proton beam dump RF gun Laser p Proton diagnostics BTV,OTR, CTR e - spectrometer Plasma cell  Rb vapour source Proton beam  drives the plasma wakefield + undergoes self-modulation instability.  LHC-type proton beam, 400 GeV/c, 3E11 protons/bunch,  = 400 ps long Laser beam:  ionizes the plasma + seeds the self-modulation instability of the proton beam.  4.5 TW laser, 100 fs Diagnostics  BTVs, OTR, CTR Electron source and beam  Witness beam to ‘surf’ on the wakefield and get accelerated  16 MeV/c, 1.2 E9 electrons/ bunch,  = 4ps long Electron spectrometer system