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 GenerationFiber 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) Frep=88.173502 MHz1550 nm

DET10A

780 nm (doubler)

Laser head

88. 173 MHz from external ThorLabs photo diode

BLP-90 3 dB AM-1431 6 dB DCB NLP-10090 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 diodePower to SSA Remarks 10 Hz to 10 MHz jitter

1. -0.6 dBm Laser unlocked 4.8 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

JitterDrift

10 Hz

Plot normalized to carrier

amplitudeFrequency range Jitter [fs]

1 Hz – 10 Hz (drift) 4798

10 Hz – 100 Hz 373

100 Hz – 1 kHz 112

1 kHz – 10 kHz 49

10 kHz – 100 kHz 51

100 kHz – 1 MHz 146

1 MHz – 10 MHz 466

√ 𝑗12+ 𝑗2

2+…+ 𝑗𝑛2

10 Hz to 1 MHz: 0.4 ps

Jitter: ‘area below curve’

Measurements at MPP

“Fiber Ring Oscillator”(Comb) Frep=88.173502 MHz1550 nm

DET10A

780 nm (doubler)

Laser head

88. 173 MHz from external ThorLabs photo diode

BLP-90 3 dB AM-1431 6 dB DCB NLP-10090 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) Frep=88.173502 MHz1550 nm

DET10A

780 nm (doubler)

Laser system with additional MenloSystems synchronization

Laser head

88. 173 MHz from external ThorLabs photo diode

BLP-90 3 dB AM-1431 6 dB DCB NLP-10090 MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source

analyser (SSA)

DSC50SPD 10 GHz

3 GHz filter

LNA-6G

LNA-6G

MenloSystems analog FB (PID) control box

E8663BRF generator, 3 GHz

Piezo drive

MASTER:

88 MHz from DET10A photo diodePower to SSA Remarks 1 Hz to 10 MHz 10 Hz to 1 MHz

1. -0.6 dBm Laser unlocked 4.8 ps 0.42 ps

2. -0.7 dBm Initial PID settings 0.53 ps 0.21 ps

3. -0.9 dBm Final PID settings 0.55 ps 0.21 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

Photo diode at 3 GHz (in-loop, locked)

“Fiber Ring Oscillator”(Comb) Frep=88.173502 MHz1550 nm

780 nm (doubler)

Laser head

3 GHz amplified in-loop signal from 10 GHz photo diode

(via 3 dB splitter)

DCBDC Block Signal source

analyser (SSA)

DSC50SPD 10 GHz

3 GHz filter

LNA-6G

LNA-6G

MenloSystems analog FB (PID)

control box

E8663BRF 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 SSA Remarks 1 Hz to 10 MHz jitter

1. -2.2 dBm 3 GHz 0.56 ps (dominated by 10-100 Hz)

3. -0.9 dBm 88 MHz scaled to 3 GHz 0.55 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 log1034 = 30.6 db

Unphysical noise floor due to scaling

(scaled to) 3 GHz

Conclusions from measurements

1. Laser must be locked to external reference2. 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 · fML = 2.998 GHz (or very close)

New draft layout, laser part

“Fiber Ring Oscillator”(Comb) Frep=88.173502 MHz1550 nm

780 nm (doubler)

Laser head

PD10 GHz

3 GHz filter LPNA

MenloSystems analog FB (PID)

control box

Piezo drive

3 GHz low phase noise

GPS 10 MHz

PD10 GHz

3 GHz filter LPNA

Df

Photodiode

88 MHz filter LPNA 88.173502 MHz

(laser)

2997.8991 MHz(laser)

2997.8991 MHz(reference)

10 MHzAWAKE

® 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

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 fRF, 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

frep

9.97 Hz

Frac. div.25/11

fc

8.68 kHz

88.173502 MHz(laser synchronous)

fRF, SPS

200.394 MHz

VME trigger unit

VME trigger unit Laser trigger

prepulse

frep

frep

Warning AWAKEBeam with 2nd frep

1498.9495 MHz

2997.8991 MHz electron beam

Synchronization(CTRV)

Distributed frequencies (from laser room)

Signal Frequency Comment

1 AWAKE 10 MHz GPS ref. 10 MHz Absolute GPS reference

2 RF reference e-beam, feRF 2997.899068 MHz Synthesized from 10 MHz

3 Mode locker frequency, fML 88.173502 MHz fML = feRF/34

4 RF reference e-beam/2, feRF/2 1498.949534 MHz Fast bucket counters

5 200 MHz RF SPS 200.3943227 MHz fML · 25/11 for RF synchronization

6 Common frequency, fc 8.675078906 kHz fML · 25/(11 · 5 · 4620) = fML/10164

7 Laser repetition rate, frep 9.971355064 Hz fML · 25/(11 · 5 · 4620 · 870) = fc/870

Signal Comment

8 Start injection AWAKE Last fc pulse before extraction + m · 2/feRF

9 Extraction pulse Last frep pulse before extraction + n · 1/fRF,SPS (local SPS)

Also possible (e.g. for laser): Last frep pulse before extraction + k · 1/fML

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

18

CERN

CNGS

SPS

Edda Gschwendtner, CERN

SPS BA2

SPS BA3SPS RF

SPS BA4

AWAKE RF Fiber links

existing RFFiber links

existing RFFiber linksto LHC RF

19Edda Gschwendtner, CERN

Layout of the AWAKE Experiment

LLRF/synchronization(protected from radiation)

Klystron drive

Clock distribution (subject to future specification)

Note: exact locations of electronicssubject to integration studies

ps triggerfor streak camera !

Power supply UPS ?

Measurements at MPP

“Fiber Ring Oscillator”(Comb) Frep=88.173502 MHz1550 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-90 10 dB AM-1431 6 dB DCB NLP-10090 MHz low-pass Miteq low-noise amplifier DC Block 100 MHz low-pass Signal source

analyser (SSA)

88 MHz output of laser headPower to SSA Remarks 1 Hz to 10 MHz jitter

1. 0.1 dBm Reference case 15 ps (12 ps)

2. -10.0 dBm Additional 10 dB before SSA 15 ps (12 ps)

3. -8.1 dBm (!) Additional 10 dB before amplifier 11 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

88 MHz from E8663B generatorPower to SSA Remarks 1 Hz to 10 MHz jitter

1. 0.9 dBm Reference case 0.76 ps

2. -11.0 dBm Additional 10 dB before SSA 0.77 ps

3. -10.9 dBm (!) Additional 10 dB before amplifier 1.64 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

88 MHz from DET10A (locked)Power to SSA Remarks 1 Hz to 10 MHz jitter

1. -0.9 dBm Final PID settings 0.55 ps (dominated by 1-10 MHz)

2. -11.6 dBm 10 dB after photo diode 1.7 ps (increased noise floor)

3. -11.2 dBm 10 dB after 1st filter 1.6 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

Comparison with E8663B (3 GHz)Power to SSA Remarks 1 Hz to 10 MHz jitter

1. -2.2 dBm DSC50S diode, locked 0.56 ps (dominated by 10-100 Hz)

2. 5.4 dBm E8663B generator 0.13 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) Frep=88.173502 MHz1550 nm

DET10A

780 nm (doubler)

Laser head

88. 173 MHz from external ThorLabs photo diode

BLP-90 2 dB DCB NLP-10090 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 SSA Remarks 1 Hz to 10 MHz jitter

1. -8.3 dBm Reference 15 ps

2. -15.7 dBm 10 dB after photo diode 8.6 ps (photo diode current?)

3. -18.3 dBm 10 db in front of SSA 12 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