Synchronization Overview

Transcription

1 Synchronization Overview S. Simrock, DESY ERL Workshop 2005 Stefan Simrock DESY

2 What is Synchronization Outline Synchronization Requirements for RF, Laser and Beam Timing stability RF amplitude and phase stability Design of RF synchronization systems Measured Performance Conclusion ERL Workshop 2005 Stefan Simrock DESY

3 Synchronization Definition of Synchronization [1] coordinating by causing to indicate the same time [2] an adjustment that causes something to occur or recur in unison [3] the relation that exists when things occur at the same time What is to be synchronized in accelerators: RF reference signals Laser pulses (Photocathode laser, seed laser, pumpe-probe laser, new: master oscillator lasers) Electrical and optical timing signals Charged particle beams (bunch arrival time) ERL Workshop 2005 Stefan Simrock DESY

4 Synchronisation in FELs RF Gun harmonic cavity llrf Laser llrf inj. RF cavities llrf RF Ref Bunch compressor Linac RF LLRF cavities RF Ref longitudinal diagnostics undulator Diag s z = 100fs s t = 100 fs? s E /E= 1e-4 (intra & inter bunch) experimental setup laser for pump probe exp. ~ M.O. RF Reference System ERL Workshop 2005 Stefan Simrock DESY

5 Synchronisation in ERLs (example) RF Gun s z = 20 ps laser beam loss (scraping) s E /E=1e-4 s j =0.06deg injector rf s t =1ps bunch compressor M56 s E /E= few % s I =1-10mA s j =0.5deg s z = 2 ps 10 MeV 100 ma Undulator(s) beam disruption ( )mA Linac RF s E /E=3e-4 s j =0.2deg 5 GeV s z = ps s t = 100 fs s E /E= 1e-4 (intra & inter bunch) bunch compression 10 MeV beam dump M56 ERL Workshop 2005 Stefan Simrock DESY

6 ERL Projects in the World Cornel BNL LBNL BINP Daresbury Erlangen CHESS PERL LUX MARS 4GLS Beam energy GeV Max.Current ma Min.bunch length < ps Min.emittance <1 0.3 nm CHESS 4GLS 4

7 Requirements Derived from beam parameters: Energy Stability and Energy spread Emittance Bunch length Arrival time Subsystem Requirements Timing and Synchronization - Photocathode Laser, Seed laser, pump probe laser, beam diagnostics (streak camera) - RF reference frequencies RF amplitude and phase stability (RF gun, Injector, Linac) ERL Workshop 2005 Stefan Simrock DESY

8 Error sources for timing, bunch length and energy spread in ERLs Laser timing jitter (reduced by bunch compressor) RF Stability - RF Gun - harmonic cavity - rf section before bunch compressor (off-crest) 1 - linac rf 2 Stability of magnets (bunch compression, phase for energy recovery) 1. Requires up to 1e-4 for ampl. and up to 0.05 deg. in phase 2. Disturbed by beam disruption in beam insertion devices (undulators) and beam instabilities (BBU) ERL Workshop 2005 Stefan Simrock DESY

9 Various factors may affect beam performance M. Borland

10 Jitter budgets for LCLS and TESLA for 0.1% energy spread and 12% current modulation. (without beam arrival timing requirement ) P. Emma, T. Limberg

11 RF phase stability in some existing machines Phase [ S band] RF Amplitude [arb. units] measured RF stability R. Akre,, LCLS klystron phase rms 0.07 (20 sec) Time [sec] sigma = 0.06% klystron ampl.. rms 0.06% (60 sec) Klystron 3 Phase (Deg) rms Time (s) Phase [ S band] MIT Bates Linac RF Zolfaghari, Cheever, Wang, Zwart ~0.07 degree(rms) level Rossendorf, cw scrf, Gabriel ~0.02 degree (rms) level Time [klystron pulses] SPPS beam results suggest this RF stability already exists in SLAC linac JLAB, cw scrf, ~0.01 degree rms level 0.01% rms amplitude level

12 RF Regulation TESLA Cavity (Simulation) Gradient Phase Beam Current Lorentz Force Detuning Lorentz Force Detuning Microphonics Microphonics Gradient Phase XFEL WORKSHOP, SLAC 2004 Stefan Simrock DESY

13 Agilent Labs Phase-Locked Loops: A Control Centric Tutorial May 8, 2002 PLL Basics Phase Detector Loop Filter Reference Signal Signal Phase-Locked to Reference Voltage Controlled Oscillator Basic idea of a phase-locked loop: inject sinusoidal signal into the reference input the internal oscillator locks to the reference frequency and phase differences between the reference and internal sinusoid = k or 0 Internal sinusoid then represents a filtered version of the reference sinusoid. For digital signals, Walsh functions replace sinusoids ACC 4 COMMUNICATIONS AND OPTICS RESEARCH LAB

14 Agilent Labs Phase-Locked Loops: A Control Centric Tutorial May 8, 2002 General PLL Block Diagram Phase Detector Loop Filter Reference Signal Signal Phase-Locked to Reference Voltage Controlled Oscillator A phase detector (PD). This is a nonlinear device whose output contains the phase difference between the two oscillating input signals. A voltage controlled oscillator (VCO). This is another nonlinear device which produces an oscillation whose frequency is controlled by a lower frequency input voltage. A loop filter (LF). While this can be omitted, resulting in what is known as a first order PLL, it is always conceptually there since PLLs depend on some sort of low pass filtering in order to function properly. A feedback interconnection. Namely the phase detector takes as its input the reference signal and the output of the VCO. The output of the phase detector, the phase error, is used as the control voltage for the VCO. The phase error may or may not be filtered ACC 5 COMMUNICATIONS AND OPTICS RESEARCH LAB

15 S-DALINAC Self Excited Loop Masteroscillator Phase Control Amplitude Control Klystron Limiter Loop Phase Amplitude Set Point Amplitude Detector Phase Set Point Phase Detector

16 Phase noise and timing jitter t rms = 2 f f 1 2 L(f )df 2πf 0 John Corlett, July 2004

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18 Although there are very good low-noise sapphire loaded cavity oscillators John Corlett, July 2004

19 Phase noise spectrum requirement Master oscillator phase noise within bandwidth of feedback systems can be corrected Residual uncontrolled phase noise plus noise outside feedback systems bandwidth results in timing jitter and synchronization limit John Corlett, July 2004

20 Performance Measured at JLAB XFEL WORKSHOP, SLAC 2004 Stefan Simrock DESY

21 Bode Plot of Controller at JLAB XFEL WORKSHOP, SLAC 2004 Stefan Simrock DESY

22 Noise characterization of the LLRF System (TTF2) n RF digital feedback system (TTF2) : n +I,-I,+Q,-Q detection scheme : Rotation of the LO-signal in four 90 o steps (-I,+Q) Im (+I,+Q) (-I,-Q) Re (+I,-Q) Phase modulation Bandwidth for transforming 250kHz squared pulses : f 10MHz Required regulation bandwidth only : f 1MHz Frank Ludwig /

23 Noise characterization of the LLRF System (TTF2) n Stability requirements on phase and amplitude of the cavity field vector : da A Amplitude stability : 4 <10 and linearity Phase stability : df < A df da du XFEL < 100µV (normalized to A=1V) n Noise measurement at input of an ADC : d U 1.0mV = 10 d TTF2 U XFEL voltage 2mV/div ACC5, Probe DCW, AN-36 time 100ns/div rms-voltage noise : du = S ( f ) df f U S U f Reduce the measuring bandwidth Low-noise design Averaging, switched low-pass! Correlation methods Superposition of all noise contributions : du DWC + duiq + dumo + duextern+... < 100µV 2 Frank Ludwig /

24 Noise characterization of the LLRF System (TTF2) n Noise from sensor (down-converter) : d U 2. 0 d DWC U XFEL P RF [ 40dBm, 10dBm], 70dB linearity SU, S U, AMP 2 S U, + SU, AMP) v SU, DWC ( = f RF v S U, DWC S U, 4.5nV / Hz, v 8.5 S AMP U, 7nV / Hz f LO S DWC U, 70nV / Hz Frank Ludwig /

25 Noise characterization of the LLRF System (TTF2) n Noise conversion over the LO-Signal at down-converter from master-oszillator : d U 10 d MO U XFEL Frank Ludwig /

26 Specifications provide FEL pulse with some ten fs arrival time stability: amplitude and phase stability of RF in cavities in injector area stable reference distributed over 3.5 km to end of linac Crucial are cavities up to bunch compressor. Jitter in I and Q of RF results in jitter in energy (off crest acceleration). Bunch compressor turns that into arrival time jitter.

27 Modelocked fiber laser oscillator rf stabilized Modelocked Fiber Laser Oscillator RF Stabilized 17 dbm mixer RF Clock 1.3/n GHz 1/T rep f BPF 1.3 GHz 28 db AMP LPF T rep Amplifier Modelocked Laser 1.3 GHz error signal Phase-lock all lasers to master oscillator Derive rf signals from laser oscillator Fast feedback to provide local control of accelerator rf systems Synchronization 10 s fs John Corlett, July 2004

28 Experimental Setup for RF Locking fs Laser 2 fs Laser MHz Delay BBO SHG SHG SFG 14 GHz Phase shifter 14 GHz 50 ps 14 GHz Loop gain 100 MHz Loop gain Sampling scope Laser 1 repetition rate control SFG intensity analysis Phase shifter fs lasers share pump source, isolated optical table RF phase shifter gives electronically addressable timing delay Jun Ye s lab in collaboration with Henry Kapteyan and workers

29 Timing Jitter via Sum Frequency Generation Cross-Correlation Amplitude 1 0 Top of cross-correlation curve (two pulses maximally overlapped) Timing jitter 1.75 fs (2 MHz BW) Timing jitter 0.58 fs (160 Hz BW) (two pulses offset by ~ 1/2 pulse width) Total time (1 s) 30 fs Noise spectrum (fs 2 /Hz) Mixer/Amplifier noise floor Locking error signal Fourier Frequency (khz) Ma et al., Phys. Rev. A 64, (R) (2001) Sheldon et. al. Opt. Lett (2002).

30 Balanced Cross-Correlator Output ( nm) tt t Cr:fo -GD/2 Ti:sa (1/496nm = 1/833nm+1/1225nm). Rep.-Rate Control 0V SFG SFG 3mm Fused GD Silica Schibli et al Opt. Lett, 28, 947 (2003)

31 Balanced Cross-Correlator Error Signal

32 Cross-Correlation Amplitude Experimental result: Residual timing-jitter Time [fs] Timing jitter 0.30 fs (2.3MHz BW) 40 Time [s] The residual out-of-loop timing-jitter measured from 10mHz to 2.3 MHz is 0.3 fs (a tenth of an optical cycle)

33 RF System Response Gradient modulator drive signals with and without energy recovery in response to 250 µsec beam pulse entering the RF cavity Volts µs without ER with ER Time(µs) Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy Thomas Jefferson National Accelerator Facility L. Merminga SRI /25/2003

34 RF Instabilities ƒ Instabilities can arise from fluctuations of cavity fields. ƒ Two effects may trigger unstable behavior: Beam loss which may originate from energy offset which shifts the beam centroid and leads to scraping on apertures. Phase shift which may originate from energy offset coupled to M 56 in the arc ƒ Instabilities predicted and observed at LANL, a potential limitation on high power recirculating, energy recovering linacs. M 56 is the momentum compaction factor and is defined by: = E l M56 E LLRF Workshop, L. Merminga 4/25/2001 Thomas Jefferson National Accelerator Facility Operated by the Southeastern Universities Research Association for the U. S. Department of Energy

35 RF STABILITY FLOW CHART Ε Energy Aperture M 56 Freq. shift G Beam loss P light Phase shift V b X Feedback V c LLRF Workshop, L. Merminga 4/25/2001 Thomas Jefferson National Accelerator Facility Operated by the Southeastern Universities Research Association for the U. S. Department of Energy

36 JAERI Energy-Recovery Linac for 10kW FEL (2002-) 17MeV Loop undulator 2.5MeV Injector 230kV E-gun 500MHz SCA (7.5MV x 2) 500MHz SCA (1MVx2) beam dump 20m Energy = 17MeV Natural extension of the original configuration. 8 times larger e-beam power. Fitting to the concrete boundary. FEL : λ = ~22µm Bunch charge =500pC Bunch length = ~15ps (FWHM) Bunch rep. = 10.4MHz 83.3MHz Average current = 5.2mA 40mA after injector-upgrade

37 Demonstration of Energy Recovery recirculation acc. dec. acc. dec. w/ ER beam load w/o ER Beam current at the exit of the second main module. RF amp forward power for the 1st main module. Bunch interval is 96ns, and recirculation time is 133ns. 98% energy of e-beam is recovered.

38 Improvement of RF Stability new low-level controllers and reference-signal cables phase drift < 0.2 deg. phase drift ~ 3 deg./o C phase jitter σ= 0.78 deg. phase jitter σ= 0.15 deg.

39 LOLA Bunch Length Measurement 1ps ERL Workshop 2005 Stefan Simrock DESY

40 Bunch Profile and Time Jitter time [ps] 2ps bunch profile 0 30 bunch # [~sec] 1ps ERL Workshop 2005 Stefan Simrock DESY

41 Drift ACC1 (cryomodule before BC) at TTF energy jitter 1e-3 time jitter 30 min 1ps 30 min ERL Workshop 2005 Stefan Simrock DESY

42 Work to be done Develop error budget for synchronization and rf field stability. Precise control of the accelerating fields in presence heavy beam loading in the injector high loaded Q in the linac (low beam current but strong fluctuations possible) Synchronize Lasers and RF Systems at various frequencies separated by distances of up to a few hundred meters. Develop highly stable phase reference systems Develop beam based correction schemes. Develop synchronization between lasers and rf systems and demonstrate performance in the accelerator environment. ERL Workshop 2005 Stefan Simrock DESY