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Phase Synchronisation Systems

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.

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Phase Synchronisation Systems

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  1. 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

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

  3. Categories of Timing Problems • Stability • Oscillators shift period with temperature, vibration etc. • Voltage Controlled Oscillator (VCO) shifts period with applied voltage • Atomic clock Df/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. Oscillators VCO or Magnetron Oscillator Oscillator using amplifier sensitive to temperature RF Output Filter RF Output Input and reflection on output port reflection on output port DC Input (changes frequency) DC Input (Changes phase) Phase Locked Loop (Synchronises oscillators at different frequencies, jitter follows performance of microwave oscillator and long term stability follows crystal oscillator) Low Pass Filter / integrator Frequency divider /N Crystal Oscillator Phase Detector Microwave Voltage Controller Oscillator Frequency divider /R Particle Accelerator Engineering, London 2014

  5. Clock to Cavity LLRF control - feedforward to next pulse based on last pulse and environment measurements Optical clock signal Locked microwave oscillator Solid state amplifier IQ modulator Extremely sensitive to modulator voltage Solid state amplifier TWT amplifier Klystron Waveguide Absolute timing impossible as every component and connector adds phase uncertainty Waveguide Pulse compressor Waveguide sensitive to temperature Cavity

  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 Phase shifter Double Balance Mixer 2.45 GHz Panasonic 2M137 1.2 kW Magnetron Spectrum Analyzer Oscilloscope controls power Stub Tuner 1 Stub Tuner 2 Loop Coupler Load 3 Loop Coupler Circulator 3 Phase shifter 1W Amplifier Load 2 Circulator 2 Cathode heater control Load 1 LP Filter 8 kHz cut-off IQ Modulator (Amplitude & phase shifter) DAC ADC Oscilloscope Control Voltage Sets current from modulator and can be in control loop to minimise phase change through magnetron, (or to source) DAC Digital Phase Detector HMC439 High Voltage Transformer Digital Signal Processor ÷ 2 ÷ 2 42 kHz Chopper Pulse Width Modulator SG 2525 Agilent E4428 signal generator providing 2.45 GHz Unwanted 300 V DC +5% 120 Hz ripple 1.2 kW Power Supply

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

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

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

  11. Daresbury Test 2009

  12. CLIC Cavity Synchronisation CLIC bunches ~ 45 nm horizontal by 0.9 nm vertical size at IP. Cavity to Cavity Phase synchronisation requirement So need RF path lengths identical to better than c Dt = 1.3 microns

  13. RF path length measurement RF path length is continuously measured and adjusted 4kW 5ms pulsed 11.8 GHz Klystron repetition 5kHz Cavity coupler 0dB or -40dB Cavity coupler 0dB or -40dB Waveguide path length phase and amplitude measurement and control Forward power main pulse 12 MW Single moded copper plated Invar waveguide losses over 40m ~ 3dB -30 dB coupler -30 dB coupler Expansion joint Expansion joint LLRF Magic Tee LLRF Reflected power main pulse ~ 600 W Reflected power main pulse ~ 500 W Phase shifter trombone Phase shifter trombone (High power joint has been tested at SLAC) Waveguide from high power Klystron to magic tee can be over moded Phase Shifter Main beam outward pick up Main beam outward pick up From oscillator 48MW 200ns pulsed 11.994 GHz Klystron repetition 50Hz Vector modulation 12 GHz Oscillator Control

  14. Laser Distribution Diagram from Florian Loehl, Cornell University

  15. The pulses sit on the zero-crossings of VCO output when it is locked. VLF j t Laser to RF Loop filter F(s) f = f0 + KVLF VCO j Balanced detector t Ti:sapphire ML-laser 2GHz phase modulator 100MHz Rep rate lRF/2 Diagram from J.W.Kim et al. MIT p/2

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