State of the Art in RF Control

Transcription

1 State of the Art in RF Control S. Simrock, DESY LINAC 2004, Lübeck Stefan Simrock DESY

2 Outline RF System Architecture Requirements for RF Control RF Control Design Considerations Design Efforts Worldwide Measured and Predicted Performance Conclusion LINAC 2004, Lübeck Stefan Simrock DESY

3 RF System Architecture master oscillator ~ actuator A&P RF power amplifier power transmission cavity Timing to LO PS for./ref. power freq. tuner LO DAC DSP/FPGA ADC DAC ADC digital/analog feedback controller A & P cavity field detector down converter LINAC 2004, Lübeck Stefan Simrock DESY

4 A. Frequency generation (1) Phase stable reference frequency oscillator (2) Phase locked Oscillators (various frequencies) (3) Power supply (4) Diagnostics (5) Control system interface (6) Phase stability monitoring and correction B. Frequency and Reference Phase Distribution (1) Phase stable transmission line (2) Temperature stabilization (3) Power distribution (directional couplers) C. Cavity Field Control (LLRF) (1) Detectors for accelerating field (a) amplitude detector (b) phase detector (c) I/Q detector RF Subsystems (2) Actuators for amplitude and phase of incident wave (a) pin-attenuator (b) multiplier (c) phase-shifter (d) vector-modulator (3) Field error detection (4) Cavity field controller with Feedback and Feedforward (5) Interlock system (6) Diagnostics (7) Interface to control system D. High Power Amplifier (1) RF power source (2) Power supply (3) Interlocks (4) Diagnostics (5) Interface to control system E. Power Transmission System (1) Transmission line (coaxial, waveguide) (2) Circulator, Isolator (3) Power dividers (4) Directional couplers (Monitor) (5) Waveguide (coaxial) window (6) Pressurisation system F. Accelerating System (1) Cavity (2) Fundamental Coupler (3) Higher Order Mode Coupler G. Cavity Frequency Tuning System (1) Cavity tuner (fast and/or slow) (a) Ferrite loaded (b) Motor tuner (c) Magnetostrictive (d) piezoelectric (e) coupled variable reactance (VCX tuner) LINAC 2004, Lübeck Stefan Simrock DESY

5 RF Control Requirements Maintain Phase and Amplitude of the accelerating field within given tolerances to accelerate a charged particle beam Minimimize Power needed for control RF system must be reproducible, reliable, operable, and well understood. Other performance goals - build-in diagnostics for calibration of gradient and phase, cavity detuning, etc. - provide exception handling capabilities - meet performance goals over wide range of operating parameters LINAC 2004, Lübeck Stefan Simrock DESY

6 Requirements RF Control Derived from beam properties - energy spread - emittance - bunch length (bunch compressor) - arrival time Different accelerators have different requirements for field stability (approximate RMS requirements - 1% for amplitude and 1 deg. for phase (example: SNS) - 0.1% for amplitude and 0.1deg.for phase (linear collider) - up to 0.01% for amplitude and 0.01 deg. for phase (XFEL) Note: Distinguish between correlated and uncorrelated error LINAC 2004, Lübeck Stefan Simrock DESY

7 Nominal LCLS Linac Parameters for 1.5-Å FEL Single bunch, 1-nC 1 charge, 1.2-µm slice emittance, 120-Hz repetition rate 6 MeV σ z 0.83 mm σ δ 0.05 % rf gun Linac-0 L =6 m new...existing linac 135 MeV 250 MeV σ z 0.83 mm σ z 0.19 mm σ δ 0.10 % σ δ 1.6 % Linac-X L =0.6 m ϕ rf = 160 Linac-1 Linac-2 L 9 9 m L 330 m ϕ rf 25 ϕ rf 41 DL-1 L 12 m R b1b 21-1d1d (RF phase: φ rf = 0 is at accelerating crest) P. Emma, SLAC X BC-1 L 6 6 m mm R b 24-6d SLAC linac tunnel Linac-3 L 550 m ϕ rf a undulator BC c L =130 m L 22 m mm LTU L =275 m R 56 0 R GeV σ z mm σ δ 0.71 % 14.1 GeV σ z mm σ δ 0.01 % research yard John Corlett, July 2004

8 Jitter Tolerance Levels in the LCLS X-band X- Jitter Jitter tolerance tolerance budget budget for for LCLS LCLS based based on on the the many many sensitivities sensitivities LCLS and test the budget with jitter simulations s z jitter = 14 % rms rms Dt-jitter = 109 fs Jitter Jitter simulation, simulation, tracking tracking particles 5 particles times, times, where where each each run run is is randomized randomized in in its its main main rf-parameters rf-parameters according according to to the the tolerance tolerance budget budget P. Emma, SLAC John Corlett, July 2004

9 Parameters and Requirements CESR-c ERL buncher cavity ERL s.c. inject. cavities ERL s..c. main linac cavities frequency [MHz] number of cavities cells per cavity R/Q / cavity (circuit def.) [W] Q to ,000 > > Q ext to ,900 > ( ) for 25 Hz peak detuning acc. voltage per cavity [MV] 1.9 to (3)» 16 required klystron power per cavity [kw] up to required relative amplitude stability (rms) < 1 % required phase stability (rms) < CORNELL Matthias Liepe 7/30/ U N I V E R S I T Y

10 Typical Parameters in a Pulsed RF System fill flat-top ampl. accelerating voltage Beam Loading incident power beam pulse... cavity phase time cavity detuning Beam pulse pattern (micro and midi pulse structure) LINAC 2004, Lübeck Stefan Simrock DESY

11 Sources of Perturbations o Beam loading - Beam current fluctuations - Pulsed beam transients - Multipacting and field emission - Excitation of HOMs - Excitation of other passband modes - Wake fields o Cavity drive signal - HV- Pulse flatness - HV PS ripple - Phase noise from master oscillator - Timing signal jitter - Mismatch in power distribution o Cavity dynamics - cavity filling - settling time of field o Cavity resonance frequency change - thermal effects (power dependent) - Microphonics - Lorentz force detuning o Other - Response of feedback system - Interlock trips - Thermal drifts (electronics, power amplifiers, cables, power transmission system) LINAC 2004, Lübeck Stefan Simrock DESY

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

13 Microphonics at JLAB LINAC 2004, Lübeck Stefan Simrock DESY

14 Control Choices (1) Self-excited Loop (SEL) vs Generator Driven System (GDR) Vector-sum (VS) vs individual cavity control Analog vs Digital Control Design Amplitude and Phase (A&P) vs In-phase and Quadrature (I/Q) detector and controller LINAC 2004, Lübeck Stefan Simrock DESY

15 Control Choices (2) M.O. Phase Controller Amplitude Controller Klystron ~ Φ A Phase Setpoint Φ Generator Driven Resonator Phase Detector Gradient Detector Gradient Set Point Cavity Limiter Phase Controller Amplitude Controller Klystron Φ A Φ Loop Phase Gradient Detector Gradient Set Point Self Excited Loop M.O. ~ Φ Phase Setpoint Phase Cavity LINAC 2004, Lübeck Stefan Simrock DESY

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20 Digital Control at the TTF master oscillator Im vector modulator DAC DAC Re klystron 1.3 GHz Cavity 1 Cavity 8 cryomodule GHz khz clock LO f = 1 MHz s a -b b a ( ) ADC 8x khz power transmission line 1.3GHz field probe.... LO ( ) a -b a 1 b 8 ADC... Cavity 25 cryomodule 4... LO a -b ( b a ) 25 ADC 8x... Cavity LO a -b ( b a ) 32 ADC Σ vector-sum feed forward table Re + Im + Re Im gain table Re Im Re setpoint table Im digital low pass filter DSP system Linac 2004 Stefan Simrock DESY

21 Digital I/Q Detection mixer RF local oscillator (LO) 1300 MHz MHz IF 250 khz amplitude x 1 x 0 x 2 0 U cos(ωt+ φ) time [µs] downconversion of cavity field to IF frequency at 250 khz - complete phase and amplitude information of the accelerating field is preserved. x 3 sample IF signal at 1MHz rate subsequent samples describe real and imaginary component of the cavity field. Linac 2004 Stefan Simrock DESY

22 Beam Transient based Phase and Gradient Calibration beam induced transient Module 2 E acc P inc (open loop) 0 Ibeam 1 2 φ cav time beam induced transient field decay for t << τ cav : φ Re(E acc ) beam V ind = I t r --- π f Q cavity filling Linac 2004 Stefan Simrock DESY

23 Adaptive Feedforward Feed Forward Real Part ( ff(t) ) [bits] Step time [µs] E( τ 1 ) Closed Loop System T 11 T 12 T 1n Real ff 1 Part ( E(t) ) [ΜV/m] Vector Sum Step Response measured calculated for a linear time-invariant System time [µs] E( τ 2 ) E( τ n ) = T 21 T 22 T 2n T n1 T n2 T nn ff n ff n ff () t = ff j Θ( t t j ). j Linac 2004 Stefan Simrock DESY

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31 System Identification (1) Cavity-Field ω V 1 2 ω = ω ω 1 2 V + Rω 1 2 ( I G + I B ) Beam-Phase smoothed & derived Forward-Power smoothed Differential Equation Bandwidth smoothed ω V 1 2 ω = ω ω 1 2 V + Rω 1 2 ( I G + I B ) Beam-Current Detuning during Pulse Linac 2004 Stefan Simrock DESY

32 System Identification (2) st Order ID on Cavity 7 Single Pulse Detuning Measurement Pf P r force P f to be zero at end of pulse by substraction of d f *P r (complex) the whole shape changes V acc f/hz, f/hz 2, V 2 /2MV ω(t) beam phase/ Correct for directivity of couplers time/µs No of Measurement Beam phase of 4 cavities for different phase of V acc Linac 2004 Stefan Simrock DESY

33 Performance at TTF (1) accelerating gradient [MV/m] with feedback and feedforward compensation only feedback (gain = 70) Zoomed Region beam time [µs] Amplitude accelerating phase [deg] only feedback (gain = 70) with feedback and feedforward compensation Zoomed Region beam time [µs] Phase Linac 2004 Stefan Simrock DESY

34 Performance at TTF (2) Operation with long beam pulses Linac 2004 Stefan Simrock DESY

35 DSP and ADC board LLRF for TTF I Linac 2004, Lübeck Stefan Simrock DESY

36 Rack Layout and Cabling for TTF I Linac 2004, Lübeck Stefan Simrock DESY

37 C67 DSP board Linac 2004, Lübeck Stefan Simrock DESY

38 Installation Status of LLRF for ACC 2-6 Zeuthen, Jan Stefan Simrock DESY

39 C67 DSP board Linac 2004, Lübeck Stefan Simrock DESY

40 Downconverter Linac 2004, Lübeck Stefan Simrock DESY

41 FPGA based RF Gun Controller Linac 2004, Lübeck Stefan Simrock DESY

42 Cavity Simulator Linac 2004, Lübeck Stefan Simrock DESY

43 SNS Controller and Initial Performance Test sc-cavity nc-cavity L. Doolittle LINAC 2004, Lübeck Stefan Simrock DESY

44 New Field Control Module for SNS L. Doolittle LINAC 2004, Lübeck Stefan Simrock DESY

45 Measurement Phase Noise L. Doolittle LINAC 2004, Lübeck Stefan Simrock DESY

46 RF Vector Control Scheme RF IF=50MHz ADC 10 MHz FPGA DAC ~ LO clock=40 MHz 50 MHz LO L. Doolittle LINAC 2004, Lübeck Stefan Simrock DESY

47 LLRF Proposal for CEBAF Upgrade C. Hovater LINAC 2004, Lübeck Stefan Simrock DESY

48 Proposal for RIA LLRF C. Hovater LINAC 2004, Lübeck Stefan Simrock DESY

49 LINAC 2004, Lübeck Stefan Simrock DESY

50 AD 8302 phase linearity ( f=25 Hz) linearity log(a) LINAC 2004, Lübeck Stefan Simrock DESY

51 AD 8302 (Cnt d) noise at output hysteresis effect LINAC 2004, Lübeck Stefan Simrock DESY

52 LINAC 2004, Lübeck Stefan Simrock DESY

53 AD8361 Temperature Stability Linearity LINAC 2004, Lübeck Stefan Simrock DESY

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55 AD 8347 Amplitude (P_in) Linearity Phase (P_in) LINAC 2004, Lübeck Stefan Simrock DESY

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57 HMC439 Linearity Noise LINAC 2004, Lübeck Stefan Simrock DESY

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59 Field Detector and Act. for Ctrl (Darmstadt) LINAC 2004, Lübeck Stefan Simrock DESY

60 Requirement for CEBAF (JLAB) LINAC 2004, Lübeck Stefan Simrock DESY

61 Bode Plot of Controller at JLAB LINAC 2004, Lübeck Stefan Simrock DESY

62 Performance Measured at JLAB LINAC 2004, Lübeck Stefan Simrock DESY

63 Performance Measure at JLAB LINAC 2004, Lübeck Stefan Simrock DESY

64 Performance at Rossendorf LINAC 2004, Lübeck Stefan Simrock DESY

65 Stability Measured for J-PARC % deg. S. Michizono LINAC 2004, Lübeck Stefan Simrock DESY

66 Matthias Liepe CORNELL CESR MO 11.9 MHz U N I V E R S I T Y Pkly MHz RF system vector synthesizer modulator Pt1 Pt2 Q I LO MHz MHz ADC ADC ADC ADC DAC DAC I Ultra-Fast Digital RF Field Control System for CESR and ERLs Q RF switch fast control RF on/off, trip fast interlock card FPGA DSP memory klystron link ports 4 ADCs 2 DACs DSP Virtex II FPGA memory FPGA DSP samplebuffer samplebuffer slow control + DAQ cavity ADC ADC ADC ADC DAC DAC piezo-tuner Pf Pr very low delay in the control loop (» 1 ms) Field Programmable Gate Array (FPGA) design combines the speed of an analog system and the flexibility of a digital system high computation power allows advanced control algorithms all boards have been designed in house generic design: digital boards can be used for a variety of control and data processing applications

67 Cornell s Digital RF Control System: Digital Boards: RF Down- Converters 500 MHz frequency synthesizer vector modulator CORNELL Matthias Liepe 7/30/ U N I V E R S I T Y

68 Open Loop Errors rad σ A /A PS klys. mic=0.1*f 12 LFD=+-f 12 σ I /I=10% (slow) 10-2 mic=0.1*f 12 (on crest) 10-3 Goal σ I /I=10% (fast) 10-0 LINAC 2004, Lübeck Stefan Simrock DESY

69 RMS Error as Function of Feedback Gain Error lower latency unstable less noise LINAC 2004, Lübeck Stefan Simrock DESY Gain

70 Active Compensation of Lorentz Force Detuning (1) tuning mechanism piezo He-tank + cavity Piezo-Actuator: l = 39 mm U max =150V l 4 to 5 µm at 2K f max, static 500Hz Linac 2004 Stefan Simrock DESY

71 Active Compensation of Lorentz Force Detuning (2) detuning [Hz] beam on - time without compensation with compensation fill time 900 µs constant gradient time [µs] 9-cell cavity operated at 23.5 MV/m Linac 2004 Stefan Simrock DESY Lorentz force compensated with fast piezoelectric tuner

72 Microphonics Suppression with Feedforward T. Grimm LINAC 2004, Lübeck Stefan Simrock DESY

73 rf signals for the accelerator may also be derived from the laser master oscillator ~ FEL seed lasers Laser oscillator Amplifier & conditioning Spatial profiling Amplitude control Multiply Amplifier Pulse shaping Laser oscillator ~ ~ ~ ~ ~ ~ Laser master oscillator Laser oscillator Laser oscillator Laser oscillator Amplifier & conditioning Amplifier & conditioning Amplifier & conditioning Multiple beamline endstation lasers Photocathode laser Accelerator RF signals John Corlett, July 2004

74 Timing Stabilized Fiber Links (~1 km) Fiber laser or Er/Yb-glass laser Assuming no fiber length fluctuations faster than 2L/c (~100 khz) Thermal fluctuations: ~ 20 µm (~ 100 fs) over 1 km for 0.1 C MIT Ultrafast Optics & Quantum Electronics Group

75 Conclusion Field regulation ranging from 1% to 10-4 amplitude and 1 deg. to 0.01 deg. for phase (in critical sections) will be required for future superconducting and normalconducting accelerators Noise sources for superconducting cavities are understood - Microphonics ( typ. 10 Hz) - Lorenz force detuning ( 1-3 Hz/(MV/m)^2) - Beam loading (few %) Rapid development in digital technology (DSP, FPGA, ADC, DAC) favors digital design for feedback/feedforward control. Fast Control with incident wave - feedforward for repetitive errors (beam,lfd, klystr.) - feedback (stochastic errors) LINAC 2004, Lübeck Stefan Simrock DESY

76 Limitation of feedback: Latency in Loop (limits loop gain) and Noise Limitation of feedforward: Measurement and Estimation of Perturbations Resonance control with fast tuner promising - Lorentz force compensation successfully demonstrated - For microphonics control first result promising results Present achievements in amplitude and 0.03 deg. have been achieved at QL=1e7 Outlook: Phase stability of 0.01 deg. appears feasible LINAC 2004, Lübeck Stefan Simrock DESY

77 LLRF Contributions at the LINAC 2004 MOP69 A. Hofler et al. RF Control Modelling Issues for Future Superconducting Accelerators TUP75 D. Dong et al. The High Accuracy RF Phase Detector Research for the 200 MeV LINAC TUP76 T. Kandil et al. Adaptive Feedforward Cancellation (AFC) of SInusoidal Disturbances in Superconducting RF (SCRF) Cavities TUP77 K. Fong et al. Status of RF Control System for ISAC II Superconducting Cavities TUP78 T. Jezynski at al. On-Line Diagnostics for the Low Level RF Control for the European XFEL TUP79 C. Hovater et al. A New RF System for the CEBAF Normal Conducting Cavities TUP89 S.P.M. Sekalski et al. Static Absolute Force Measurement for Preload Piezoelements Used for Active Force Force Detuning TUP98 W. Cichalewski et al. The Finite State Machine for Klystron Operation for TESLA and the European XFEL Linear Accelerator THP52 T. Kobayashi et al.. RF Reference Distribution System for J-PARC Linac THP56 S. Michizono et al. Control of Low Level RF System for J-Parc Linac THP57 S. Michizono et al. Digital Feedback System for J-Parc Linac RF Source THP59 J. Mourier et al. Low Level RF Including a Sophisticated Phase Control System for CTF3 THP66 T.L. Grimm et al. Measurement and Control of Microphonics in High Loaded-Q Superconducting RF Cavities LINAC 2004, Lübeck Stefan Simrock DESY