Particle Accelerator Engineering, London, October 2014

Phase Synchronisation Systems

Dr A.C. Dexter

Overview

Accelerator Synchronisation Examples

Categories of Timing Problems

Oscillators

Clock to Accelerator Cavity

Phase Locked Magnetrons

RF Interferometers

CLIC Crab Cavity Synchronisation

Laser Timing Distribution

Laser to RF

Particle Accelerator Engineering, London, October 2014

Accelerator Examples

Crab Cavity System IP

quadrupolequadrupole

Crab cavity Crab cavity

25 m

PositronsElectrons

Free Electron Laser

Bunch to RFOff crest acceleration

Voltage gain as function of relative position

Bunch position when RF field is maximum

Particle Accelerator Engineering, London, October 2014

Categories of Timing Problems

• Stability Oscillators shift period with temperature, vibration etc. Voltage Controlled Oscillator (VCO) shifts period with applied voltage Atomic clock f/f ~ 10-14 ~ 60 fs per minute

• Synchronisation Two clocks with different periods at same place (Phase Locked Loop) Identical delivery time/phase at two places (Crab Cavity Problem) Same clock at two places

Resynchronisation requires constant propagation time of signal Detector with high resolution and low noise

• Trigger an event at a later and a different location Needs two stable clocks which are synchronised (FEL problem) Must be able to generate event from clock pulse with tiny jitter Work at DESY and MIT suggest 10fs achievable

Particle Accelerator Engineering, London 2014

Oscillators

RF Output

DC Input(changes frequency)

Input and reflection on output port

RF Output

DC Input(Changes phase)

reflection on output port

Filter

Low Pass Filter / integrator

VCO or Magnetron Oscillator

Phase Detector

Microwave Voltage Controller Oscillator

Crystal Oscillator

Frequency divider /R

Frequency divider /N

Oscillator using amplifier

Phase Locked Loop (Synchronises oscillators at different frequencies, jitter follows performance of microwave oscillator and long term stability follows crystal oscillator)

sensitive to temperature

Clock to Cavity

Optical clock signal

Locked microwave oscillator

Solid state amplifier

IQ modulator

Solid state amplifier

TWT amplifier Klystron

Pulse compressor

Waveguide

Waveguide

Waveguide

Cavitysensitive to temperature

Extremely sensitive to modulator

voltage

LLRF control - feedforward to next pulse based on last pulse and environment measurements

Absolute timing impossible as every component and

connector adds phase uncertainty

Magnetron Exciting Superconducting Cavity

Demonstration of CW 2.45 GHz magnetron driving a specially manufactured superconducting cavity in a vertical test facility at JLab and the control of phase in the presence of microphonics was successful.

First demonstration and performance of an injection locked continuous wave magnetron to phase control a superconducting cavity A.C. Dexter, G. Burt, R. Carter, I. Tahir, H. Wang, K. Davis, and R. Rimmer, Physical Review Special Topics: Accelerators and Beams, Vol. 14, No. 3, 17.03.2011, p. 032001.

http://journals.aps.org/prstab/abstract/10.1103/PhysRevSTAB.14.032001

Circuit for Phased Locked Operation

1.2 kW Power Supply

1W Amplifier

Agilent E4428 signal generator providing 2.45 GHz

Load 2

Load 3

High Voltage Transformer

42 kHz Chopper

Pulse Width Modulator SG 2525

Stub Tuner 1

Circulator 3

Circulator 2

LP Filter 8 kHz cut-off

Unwanted300 V DC +5% 120 Hz ripple

2.45 GHz Panasonic 2M137 1.2 kW Magnetron

Loop Coupler

Stub Tuner 2

Oscilloscope

Load 1

Oscilloscope

÷ 2

ADCDACIQ Modulator(Amplitude &

phase shifter)

÷ 2

DAC

Digital Signal Processor

Digital Phase DetectorHMC439

Phase shifter

Spectrum Analyzer

Phase shifter

Control VoltageSets current

from modulator and can be in

control loop to minimise phase change through

magnetron,(or to source)

Cathode heater control

Loop Coupler

Double Balance Mixer

controls power

Phase Control Performance

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-500 -250 0 250 500Frequency offset (Hz)

Po

wer

sp

ectr

al d

ensi

ty (

dB

)

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-500 -250 0 250 500Frequency offset (Hz)

Po

wer

sp

ectr

al d

ensi

ty (

dB

)

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-500 -250 0 250 500Frequency offset (Hz)

Po

wer

sp

ectr

al d

ensi

ty (

dB

)

-15

-5

5

15

25

35

45

0.00 0.01 0.02 0.03 0.04 0.05

Time (seconds)

Cav

ity p

has

e er

ror

(deg

rees

) Control on

Control off

Injection but magnetron

off

Injection +magnetron

on

Injection +magnetron on

+control

RF Interferometer

master oscillator

phase shifter

loop filter

directional coupler

Phase shifter

loop filter

directional coupler

digital phase detector

digital phase detector

coax link

synchronous output

synchronous output

Interferometer line length adjustment Precision reflector

Position along cable

Far location

Near locationtime

Synchronisation when return pulse arrives at time when outward pulse is sent

adjust effective position of far location with a phase shifter

180o

0o

VTF Phase Control Tests

~ 15 metrelow loss

(high power)

coax linkDivider

Rhode & Schwarz SG used to generate 3.9 GHz

Load

phase detector board B

divide to 1.3 GHzsynchronous

reference signals

phase shifter

precision reflector circuit

Phase shifter

interferometer line length adjustment circuits

Phase shifter

divide to 1.3 GHz

phase detector board A

Load Load

vector mod.

16 bit A/D

cavity control

D/A

DSPdoes IQ

conversion then PI control Loop

filter

Loop filter

Manual Phase Shifter

Manual phase shifter

Manual phase shifter

IF

Load LoadPower metersPower meters

DBM

vector mod.

16 bit A/D

cavity control

D/A

DSPdoes IQ

conversion then PI control

Daresbury Test 2009

Period Jitter (degrees)

1 Cavity to cavity control off 10 secs 0.7942

2 Cavity to cavity control on 10 secs 0.0852

3 Cavity to cavity control on 0.05 secs 0.0743

4 Cavity to cavity no interferometer 10 secs 0.0888

5 Cavity to cavity no interferometer 0.05 secs 0.0763

6 Cavity to source 1 0.05 secs 0.0576

7 Cavity to source 1 10 secs 0.0600

CLIC Cavity Synchronisation

Cavity to Cavity Phase synchronisation requirement

degrees1S

1

c

f7204rmsc

x

Target max. luminosity loss fraction S

f (GHz)

x

(nm)c

(rads)rms

(deg)t (fs) Pulse

Length (s)

0.98 12.0 45 0.020 0.0188 4.4 0.156

So need RF path lengths identical to better than c t = 1.3 microns

CLIC bunches ~ 45 nm horizontal by 0.9 nm vertical size at IP.

Particle Accelerator Engineering, London, October 2014

RF path length measurement

48MW 200ns pulsed 11.994 GHz Klystron

repetition 50Hz Vector

modulationControl

Phase Shifter

12 GHz Oscillator

Main beam outward pick up

Main beam outward pick up

From oscillator

Phase shifter trombone

(High power joint has been tested at SLAC)

Magic Tee

Waveguide path length phase and amplitude measurement and control

4kW 5s pulsed 11.8 GHz Klystron

repetition 5kHz

LLRF

Phase shifter trombone

LLRF

Cavity coupler 0dB or -40dB

Cavity coupler 0dB or -40dB

Expansion joint

Single moded copper plated Invar waveguide losses over 40m ~ 3dB -30 dB

coupler -30 dB coupler

Forward power

main pulse

12 MW

Reflected power main pulse ~ 600 W

Reflected power main pulse ~ 500 W

Waveguide from high power Klystron to magic tee can be

over moded

Expansion joint

RF path length is continuously measured and adjusted

Laser Distribution

Diagram from Florian Loehl, Cornell University

Laser to RF

RF/2

f = f0 + KVLF

2GHz phase modulator

Ti:sapphireML-laser

F(s)

Loop filter

t

VCO

Balanceddetector

VLF

/2

100MHzRep rate

t

The pulses sit onthe zero-crossingsof VCO output when it is locked.

Diagram from J.W.Kim et al. MIT