Intra-train Longitudinal Feedback for Beam Stabilization at FLASH

Transcription

1 Intra-train Longitudinal Feedback for Beam Stabilization at FLASH Ch. Behrens 1), M.-K. Bock 1), M. Felber 1), P. Gessler 1), K. Hacker 1), W. Koprek 1), H. Schlarb 1), S. Wesch 1), C.Schmidt 1), S. Schulz 2), B. Steffen 1), J. Szewinski 3) 1) Deutsches Elektronen-Synchrotron, Hamburg, Germany 2) University of Hamburg, Germany 3) The Andrzej Soltan Institute for Nuclear Studies, Swierk, Poland Holger Schlarb, DESY Bjorn Wiik Prize,

2 Motivation Demanding requirements for the bunch train stability at FLASH sflash experiment HHG laser pulse length ~ 40 fs longer electron bunches with flat peak current ~ 120 fs bunch arrival time jitter < 40 fs Pump-probe experiments Two types of experiments Single shot resolved mainly interested in measurement of arrival time, repeatability Integrating experiments detectors integrate over entire macro pulses and every bunch must come at the same time beam arrival time as good as possible (<10fs out of spec) 2

3 FLASH Overview 4x3.9GHz Cavities (ACC39) New ACC module (ACC7) sflash Replaced ACC1 Replaced ACC3 New RF-Gun TUOBI2 - talk from S. Schreiber 3

4 FLASH Pulse Mode Operation Energy loading Trigger Bunch train Field decay Interrupt 100ms Trigger RF Pulse 2048 us intra-pulse Adaptation algorithms pulse-pulse algorithms t LLRF control systems stabilize field in the cavities: Intra-pulse feedback Pulse-pulse feedback Beam based feedback stabilize beam properties Intra-train feedback Pulse-pulse feedback 4

5 Beam Based Feedback Implementation Goals Actuators: LLRF Systems Sensor: Beam diagnostics fast (intra-bunch) adaptive (pulse-pulse) 5

6 Beam Diagnostic Components Toroid Toroid Toroid Laser BC2 ~~ Gun ACC1 3 rd ACC2 ACC3 ACC4 ACC7 BC3 RF Master Oscillator BAM BAM BCM BAM BCM BAM Master Laser Oscillator (MLO) Beam Arrival Monitors (BAM) Bunch Compression Monitors (BCM) Charge Measurement (by toroids) Master Laser Oscillator (MLO) 6

7 Optical Synchronization System Installation at FLASH More details in poster from Sebastian Schulz THPA05 and in the following talk by Matthias Felber 7

8 Beam Arrival Monitor Detector 8

9 Beam Arrival Monitors Front-end Electronics Top view to LLRF Bottom view More details in posters from Patrick Gessler THPA04 and THPA06 9

10 Beam Compression Measurement Detector Radiation process: electron beam passes slitted metallized screen expanded electric field from bunch is diffracted screen tilt of 45 allows observation Coherence effect: wavelength is comparable or longer than bunch length radiated power is inversely propotional to bunch length scales quadraticaly in charge Courtesy of S. Wesch (DESY) Diffraction radiator (backview) Detection: pyro electric element LiTaO3 (2mm x 2mm x 27 um) deposited heat induces surface charge metallization forms a capacitor optional black coating increases response at low λ s Pyro element 10

11 Beam Compression Measurement Front-end Electronics LLRF Oscillation at 1.17 MHz Pile-up effect 11

12 Low Level RF Control Systems Laser BC2 ~~ Gun ACC1 3 rd ACC2 ACC3 ACC4 ACC7 BC3 A A A A LLRF LLRF LLRF 2 x LLRF LLRF LLRF Systems upgrade during FLASH shutdown allowed implementation of the beam based feedback All modules controller by the same hardware board SIMCON-DSP Unified firmware and software Connected signals from beam diagnostic systems SIMCON-DSP LLRF Control Systems Stabilize amplitude and phase of the accelarting field in the cavities Intra-pulse feedback with MIMO controller Pulse-pulse algorithms (tables adaptation, calibration, ) Frequency control of the cavities using piezo sensors and actuators 12

13 Low Level RF Control Systems System setup master oscillator RF Timing Vector Modulator Klystron power transmission for/ref power cavity LO Generation LO DAC DAC Digital Feedback Board FPGA DSP ADC ADC ADC IF RF probe LO 13

14 Beam Based Feedback Installation Laser BC2 BC3 ~~ Gun ACC1 3 rd ACC2 ACC3 ACC4 ACC7 A Toroid Toroid Toroid A A A BAM BAM BCM BAM BCM BAM LLRF LLRF LLRF LLRF LLRF Beam Based Feedbacks: BAM before BC2 corrects phase in RF-Gun BAM and BCM after BC2 simultaneously correct amplitude and phase in ACC1 and 3rd harmonic BAM and BCM after BC3 correct amplitude and phase in ACC23 Results from BBF running at BC2 14

15 Low Level RF Control Systems Intra-train BBF Implementation FPGA Control Tables LLRF SP Table SIMCON-DSP Set point Beam Based Signals ADC Optolink Intra-train BBF Algorithm Intra-train beam based feedback SP Modulation Cavity Probes ADC Field Detection Vector Sum + - Error Signal Feedback Controller DAC To Klystron Intra-pulse LLRF feedback 15

16 Low Level RF Control Systems Intra-train BBF Implementation Control System Toroid ADC9 Charge Measurement Q toroid Pyro SP Table LLRF Control Tables LLRF SP Table BCM ADC10 BAM Optical Link Peak Detection t sample Gating FPGA Charge Correction Q nom - ΔU Δt Transfer Matrix ΔΦ ΔA/A I SP Signal Modulation I Q Q MPS 16

17 Low Level RF Control Systems Pulse-pulse BBF Implementation Operator & LLRF expert Setpoints: A, & Parameters: timing, Beam based SP correction Model based FF & SP tables Learning Feed forward Bunch Pattern FPGA SP_CORR table SP table FF table FF_CORR table FF_BLC table Q MPS + + Beam signals Intra-train BBF Algorithm Rot FF-total table Field detection - MIMO + Rot DAC DAC 17

18 BBF Calibration Transfer Matrix Determination BC2 Gun ACC1 ACC39 measure BAM Pyro A/ A/ t C/ z Actuators Monitor system ACC1? ACC39 scanning calculate 18

19 BBF Calibration Transfer Matrix Determination off crest ACC1 ACC39 on crest Beam Arrival Time Change >> Bunch Compression Change >> 19

20 Measurements Learning Feed Forward Operator & LLRF expert Setpoints: A, & Parameters: timing, CPU Beam based SP correction Model based FF & SP tables ratio Learning Feed forward Bunch Pattern SP_CORR table SP table FF table FF_CORR table FF_BLC table SP_BBF table Q MPS Q MPS + + FPGA Beam signals - a b c d Rot Error signal FF-total table LFF Field detection - MIMO + Rot DAC DAC 20

21 Measurements Learning Feed Forward 21

22 Measurements Learning Feed Forward 0.5 ps 4 ps 22

23 Low Level RF Control Systems Intra-train BBF Implementation FPGA Control Tables LLRF SP Table SIMCON-DSP Set point Beam Based Signals ADC Optolink Intra-train BBF Algorithm Intra-train beam based feedback SP Modulation Cavity Probes ADC Field Detection Vector Sum + - Error Signal Feedback Controller DAC To Klystron Intra-pulse LLRF feedback 23

24 Measurement Intra bunch train arrival time Conditions: Full BBF on ACC1 and ACC39 Measured after BC macro pulses taken Single RF pulse BBF latency ~ 4μs mean ~35fs - good enough for sflash? 24

25 Measurement Macro pulse arrival time jitter No Beam Based Feedback Learning Feed Forward ON rms = 74 fs With Beam Based Feedback running in ACC1 and ACC39 rms = 5 fs LLRF Regulation Performance ΔA 1 / A 1 ~10e-4 Δφ 1 < 0.03 O rapid fluctuations averaged out resolution of BAM ~ 10 fs for single shot can be reduced to ~ fs for macro pulse 25

26 Summary Commissioned interfaces between LLRF system and beam diagnostic systems Well defined and implemented a new concept of the beam BBF in the LLRF systems BBF modules set point table no direct interference with the LLRF controller feedback loop Robustness limiters on the BBF correction signals reduce risk for increased beam losses Successful tests with BBF on BC2 Prove of the concept Reduction of the intra-train bunch arrival time jitter Significant reduction of pulse-pulse beam arrival time jitter Reduction of the repetitive errors by Learning Feed Forward 26

27 Thank you for your attention References: TUOBI2 S. Scheriber, FLASH upgrade and first results THOA3 M. Felber et al., RF-based Synchronization of the Seed and Pump-Probe Lasers to the Optical Synchronization System at FLASH THPA04 P. Gessler et al., Longitudinal Bunch Arrival-Time Feedback at FLASH THPA05 S. Schulz et al., Performance of the FLASH Optical Synchronization System Utilizing Commercial SESAM-Based Erbium Laser THPA06 P. Gessler et al., Real-Time Sampling and Processing Hardware for Bunch Arrival Time Monitors at FLASH and XFEL M. K. Bock, M. Felber, P. Gessler, K. E. Hacker, F. Loehl, F. Ludwig, H. Schlarb, B. Schmidt, J. Zemella, DESY, Hamburg, Germany, S. Schulz, L.-G. Wissmann, University of Hamburg, Germany, RECENT DEVELOPMENTS OF THE BUNCH ARRIVAL TIME MONITOR WITH FEMTOSECOND RESOLUTION AT FLASH, Proceedings of IPAC 10, Kyoto, Japan F. Löhl, Optical Synchronizations of a Free-Electron Laser with Femtosecond Precision, DESY- THESIS , 2009 S. Schulz, Hamburg University, Germany, M. K. Bock, M. Felber, P. Gessler, K. E. Hacker, F. Ludwig, H. Schlarb, B. S chmidt, T. L amb, L.-G. Wissmann, Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany, Performance of the FLASH Optical Synchronization System with a Commercial SESAM-Based Erbium Laser, Proceedins of IPAC 10, Kyoto, Japan C. Behrens, B. Schmidt, S. Wesch, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany, D. Nicoletti, INFN-Roma, Roma, Italy, UPGRADE AND EVALUATION OF THE BUNCH COMPRESSION MONITOR AT THE FREE-ELECTRON LASER IN HAMBURG (FLASH), Proceedins of IPAC 10, Kyoto, Japan 27