1. 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

2. Particle Accelerator Engineering, London, October 2014 Accelerator Examples Crab Cavity System IP quadrupole Crab cavity 25 m Positrons Electrons Free Electron Laser Bunch to RF Off crest acceleration Voltage gain as function of relative position Bunch position when RF field is maximum

3. 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

4. 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

5. Clock to Cavity Optical clock signal Locked microwave oscillator Solid state amplifier IQ modulator Solid state amplifier TWT amplifier Klystron Pulse compressor Waveguide Cavity sensitive 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

6. 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

7. 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 Unwanted 300 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 ADC DAC IQ Modulator (Amplitude & phase shifter) ÷ 2 DAC Digital Signal Processor Digital Phase Detector HMC439 Phase shifter Spectrum Analyzer Phase shifter Control Voltage Sets 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

8. Phase Control Performance Injection but magnetron off Injection + magnetron on Injection + magnetron on + control

9. RF Interferometer master oscillator phase shifter loop filter directional coupler Phase shifter loop filter directional coupler digital phase detector coax link synchronous output Interferometer line length adjustment Precision reflector Position along cable Far location Near location time Synchronisation when return pulse arrives at time when outward pulse is sent adjust effective position of far location with a phase shifter 180 o 0o0o

10. VTF Phase Control Tests ~ 15 metre low loss (high power) coax link Divider Rhode & Schwarz SG used to generate 3.9 GHz Load phase detector board B divide to 1.3 GHz synchronous 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 vector mod. 16 bit A/D cavity control D/A DSP does IQ conversion then PI control Loop filter Manual Phase Shifter Manual phase shifter IF Load Power meters DBM vector mod. 16 bit A/D cavity control D/A DSP does IQ conversion then PI control

11. Daresbury Test 2009 PeriodJitter (degrees) 1Cavity to cavity control off10 secs0.7942 2Cavity to cavity control on10 secs0.0852 3Cavity to cavity control on0.05 secs0.0743 4Cavity to cavity no interferometer10 secs0.0888 5Cavity to cavity no interferometer0.05 secs0.0763 6Cavity to source 10.05 secs0.0576 7Cavity to source 110 secs0.0600

12. CLIC Cavity Synchronisation Cavity to Cavity Phase synchronisation requirement Target max. luminosity loss fraction S f (GHz)  x (nm)  c (rads)  rms (deg)  t (fs) Pulse Length (  s) 0.9812.0450.0200.01884.40.156 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.

13. Particle Accelerator Engineering, London, October 2014 RF path length measurement 48MW 200ns pulsed 11.994 GHz Klystron repetition 50Hz Vector modulation Control Phase Shifter 12 GHz Oscillator 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 5  s pulsed 11.8 GHz Klystron repetition 5kHz LLRF Phase shifter trombone LLRF Cavity coupler 0dB or -40dB Expansion joint Single moded copper plated Invar waveguide losses over 40m ~ 3dB -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

14. Laser Distribution Diagram from Florian Loehl, Cornell University

15. Laser to RF RF /2 f = f 0 + KV LF 2GHz phase modulator Ti:sapphire ML-laser F(s) Loop filter t  VCO Balanced detector V LF  /2 100MHz Rep rate t  The pulses sit on the zero-crossings of VCO output when it is locked. Diagram from J.W.Kim et al. MIT