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Acknowledgements: P. Baudrenghien, A. Butterworth, E. Ciapala, B. Goddard, A. Koschik,

LHC Transverse Damper Beam Commissioning. Wolfgang Hofle CERN AB/RF/FB. Acknowledgements: P. Baudrenghien, A. Butterworth, E. Ciapala, B. Goddard, A. Koschik, F. Killing, G. Kotzian, R. Louwerse, E. Metral E. Montesinos, V. Rossi, D. Valuch,

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Acknowledgements: P. Baudrenghien, A. Butterworth, E. Ciapala, B. Goddard, A. Koschik,

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  1. LHC Transverse Damper Beam Commissioning Wolfgang HofleCERN AB/RF/FB Acknowledgements: P. Baudrenghien, A. Butterworth, E. Ciapala, B. Goddard, A. Koschik, F. Killing, G. Kotzian, R. Louwerse, E. Metral E. Montesinos, V. Rossi, D. Valuch, V. Zhabitsky (for JINR / Dubna collaboration) Extended LTC meeting

  2. LHC Transverse Damper Beam Commissioning Outline • Overview of System, do we need the damper on day ONE ? • Readiness for beam commissioning stages of the commissioning with beam • Summary 2/22 W. Hofle / March 5, 2008 Extended LTC meeting

  3. Transverse multi bunch feedback principle Kicker Need real-time digital signal processing Match delays: t signal =t beam + MT 0 T0 : beam revolution time M=1: very common -> “One -Turn-Delay” feedback But M>1 also possible phase and delay adjustments t signal Signal processing gain g t beam D Pick-up 1 Pick-up 2 • damping: of transverse injection oscillations • feedback: curing transverse coupled bunch instabilities • excitation: of transverse oscillations for beam measurements & other applications Extended LTC meeting

  4. Why do we need Transverse damper on day ONE ? damping: transverse injection oscillations -> filamentation of injection error will lead to larger transverse emittance w/o damper even for perfect steering there are errors from the injection kicker ripple (see next slides) excitation: damper can be easily used to do a transverse excitation of the beam -> requested for the continuous tune measurement -> can be used to kick out unwanted beam (“abort gap cleaning”) etc. AB-RF-FB provides an input for the BI tune measurement, ready today feedback: curing transverse coupled bunch instabilities, necessary at start of phase B -> will become important as intensity is raised, scrubbing in regime with e-cloud present etc. present estimate (E. Metral, PAC2007, WEOAC03): 7 TeV half nominal intensity @ nominal scheme (2808 bunches) requires feedback 450 GeV ~ 1/10 of nominal stable, i.e. factor ~2 margin for 156x156 scheme phase A -> damper on only for injection damping phase B -> beam unstable w/o damper ! Extended LTC meeting

  5. Reminder: Emittance increase by filamentation without damper a steering / kick error of Dx in position and Dx’ in angle will lead to a relative emittance increase of Introducing the effective (overall) damping rate where tdec de-coherence time in absence of instability and active damping tinst instability rise-time tad active damping time as it would follow from damper gain without having any instability and without de-coherence phenomena and assuming tdec >> tinst > tad the emittance increase becomes blow-up reduction factor typically tdec > 10 x tad hence emittance increase reduced by factor >100 ! -> justifies having damper from start Extended LTC meeting

  6. Injection kicker pulse with ripple (prototype) finite rise time kicker ripple Bunch positions for 43 bunch filling pattern 243/3564=0.0682 or 6075 ns Scanning with single bunch suggested in phase A4 to verify effective kick seen by beam (see talk by V. Kain) Extended LTC meeting

  7. Results of a simulation (kicker prototype waveform) beam blowup due to injection kicker imperfections and TFB OFF (red) [normalised rms in mm] bunch positions for 43 bunch filling pattern (4 bunches injected) batch length 243x25 ns, e.g. pos. 650->893 beam emittance with TFB ON (black) within design parameters (3.75um) batch length for 156 bunch scheme is 315 bunch positions (16 bunches), longer than nominal batch of 25 ns operation (311 positions) G. Kotzian, simulations ongoing, new kicker waveforms from AB-BT for actual kickers need to be included emittance blowup in previous SPS batch Extended LTC meeting

  8. Reminder: filling patterns, kicker ripple and transverse feedback LHC Commissioning phase A: 1 to 156 bunches • Single bunch transferred from SPS to LHC: • bunch can be placed on flat part of injection kicker • no issue with ripple, just question of reproducibility shot-to-shot • 43 bunch scheme: batch transferred from SPS to LHC: • 4x(b+80e) -> length is (4x81-80-1) x 25 ns = 243 x 25 ns = 6075 ns • still some margin to place batch, 3 of the 4 bunches look OK, 1 bunch requires damper • 3) 156 bunch scheme: batch transferred from SPS to LHC: • 4x(4x(b+20e)) -> length is (4x4x21-20-1) x 25 ns = 315 x 25 ns = 7875 ns • occupies full length of kicker pulse -> damper required to preserve emittance • some margin due to adjustable kicker pulse length, but fall- (and rise- ?) time issue compare with nominal scheme 2808 bunch scheme: batch transferred from SPS to LHC: 4x(72b+8e) -> length is (4x80-8-1) x 25 ns = 311 x 25 ns = 7775 ns Extended LTC meeting

  9. LHC Transverse Damper Beam Commissioning Outline • Overview of System, why do we need the damper on day ONE ? • Readiness for beam commissioning stages of the commissioning with beam • Summary Extended LTC meeting

  10. 20 kickers 40 wideband amplifiers, i.e. 40 tetrodes (RS2048 CJC, 30 kW) 20 amplifier cases V H H H H V H H V H V H V H V H V V V V The LHC Transverse Damping System (high power part) Installed, hardware commissioning under way calibrations and phasing still need to be completed, quite some work for AB/RF group Damper system IP4 Beam 1 Beam 2 damper kicker Wideband amplifier Unit Module Status of installation and hardware commissioning: see talk by Olivier Brunner on Tuesday Extended LTC meeting

  11. feedback loop start commissioning in phase A3 close loop in phase A4: requires RF capture Overview of one damper system (there are four, one per beam and plane) low level electronics (surface) phase A1, A2 does not require capture signal levels, phasing (delay) phase A2: put excitation on beam to verify kick strength kickers and power amplifiers (tunnel) controls amplification and interlocking (UX45, underground) pick-ups (tunnel) Extended LTC meeting

  12. Beam Commissioning Phase A1 and A2First turn and circulating beam(can start before RF capture) Observation of beam at damper pick-ups Q7, Q9 and delay equalization: Verification of signal levels (sum signals) Verification of signal levels versus transverse bunch position (calibrate using orbit system) Delay equalization of damper pick-up signals from Q7 and Q9 (local adjustment in SR4) Excite transverse oscillations (phase A2) in order to check available damper kick strength [calibration of kick] Most activities do not require dedicated beam time, they can be done in the shadow of other users / MDs, except for excitation experiments -> suggest 2x4 hours dedicated time for this As beam instrumentation becomes available (position & intensity, fast BCT), compare damper signals with standard BPM readings, do calibrations work will be done by RF group, some help required from OP & BI for instruments (standard BPMs, bunch-to-bunch intensity) Extended LTC meeting

  13. intensity nomalised bunch position digitised and synchronised (two pick-ups) Overview of signal processing commission in A3 commission in A4 signal processing VME module DSPU (“Damper Loop”) based on 1T-FB module beam position VME module prototypes exist, firmware (FPGA) being developed not static, i.e. evolution of firmware to incorporate additional functionalities, upgrades, optimizations Extended LTC meeting

  14. Beam Commissioning Phase A3(after RF capture) Commissioning RF front-end (beam position module) of damper and check optics: Verify RF signals from RFLL Commission analog front-end Commission digitization and frev tagging of bunch Check phase advance Q7->Q9->damper (both beams and planes) Verify beta functions at Q7, Q9, dampers Setting-up requires stable RF conditions, so no parallel RF MDs assume 4 hours per beam and plane dedicated beam time work to be done by RF group, some help from OP and ABP required for optics check additionally 1 shift for optics checks in IR4 per beam ? Extended LTC meeting

  15. signal processing VME module (DSPU, “damper loop”) based on 1T-FB module FGC control “phase”, two functions commission in A4 Phase shifter optional not needed on day 1 Input: nomalised bunch position synchronised (two pick-ups) scaling: b-functions FGC control “delay” Built in NWA for setting-up or use of external NWA For open loop transfer function measurement Functionality on built into VME module Damper DSPU (based on 1T-FB module) FGC control “gain” Extended LTC meeting

  16. Adjustment of Phase f1 fm=f2-f1 f2 fk Kicker module Pick-up 1 Pick-up 2 beam Df We need to adjust the phase in the feedback by combining the signal from the two pick-ups in the correct way with coefficients b1 and b2, coefficient C can be chosen C=1, rendering gain independent of phase setting-up pick-up 2 (f2) kicker fm pick-up 1 (f1) coefficients for pick-up mixing b1, b2 can be calculated from optics in practice adjustment through open loop transfer function measurement target phase (kicker + 1.5 x Qf) SPS damper: open loop transfer function measurement 16/22 W. Hofle / March 5, 2008 Extended LTC meeting

  17. Beam Commissioning Phase A4[450 GeV] Commissioning Damper Loop (450 GeV): Measure de-coherence time with damper off, non-linearities corrected Measure open loop transfer function (mainly at ~low frequency) Make necessary adjustments (gain, phase, delay) Close damper loop Scan gain, phase, delay and measure damping time and stability limits for initial setting-up with one bunch assume 4 hours per beam and plane; steps to be repeated for multi-bunch operation and when intensity is increased Commission beam blow-up facility (tailoring of transverse emittance) [to produce nominal emittance at lower intensity, could also be done in SPS] Measure beam lifetime as function of damper gain scan injection kicker pulse by moving bunch initial setting-up done by RF group, some help from OP and ABP … welcome for the specialized MDs listed above, add some MD time for the specialized MDs 17/22 W. Hofle / March 5, 2008 Extended LTC meeting

  18. Beam Commissioning Phase A6[first 2 minutes of ramp] Abort gap cleaning and machine protection (start in A5, B. Goddard dixit): Check machine protection, are we protected if damper wrongly set-up, meaning: one should check with a low intensity bunch and the damper in anti-damping, if the BLMs register losses correctly and in time in order to prevent damage in case this happens with a high intensity beam dedicated MD time 2x4 hours,in collaboration with OP, BI, machine protection team Try out abort gap cleaning techniques (this requires the collimators) Optimize abort gap cleaning programs to start with assume a dedicated MD time of 2x4 hours to set-up initial abort gap cleaning in collaboration with OP, ABP, BT, collimator team 18/22 W. Hofle / March 5, 2008 Extended LTC meeting

  19. Beam Commissioning Phase A7[ramp] Commissioning Damper Loop (7 TeV): Measure open loop transfer function (low frequency) Make necessary adjustments (gain, phase, delay) Close damper loop Measure open and closed loop transfer functions Check abort gap cleaning at higher energies (this requires collimators) Would be useful to have the orbit feedback in order to optimize damper gain before digitization Count MD time in number of successful ramps ? Plan on 3 ramps for above program per beam ? Collaboration with BI, BT, ABP, collimator team … Extended LTC meeting

  20. Principal of abort gap cleaning using the transverse damper resonant excitation of transverse oscillations capture of beam by aperture limit (LHC: by collimators) amplitude can be modulated with any frequency between 1 kHz and 20 MHz; gate feedback action off during gap 1st injected batch abort gap (119 missing bunches) cleaning pulse (gate) centered in abort gap modulation of pulse with betatron frequency full amplitude up to ~ 1 MHz possible LHC nominal bunch pattern 2808 bunches 20/22 W. Hofle / March 5, 2008 Extended LTC meeting

  21. abort gap cleaning in LHC using transverse damper Simulation results for the LHC Beam 1 (450 GeV/c) LHC Model nominal with multi-poles + correction resonant excitation with damper primary collimators betatron cleaning TCP.D6L7.B1 TCP.C6L7.B1 TCP.B6L7.B1 primary collimators momentum cleaning TCP.6L3.B1 compare with MDs as early as possible Simulations (MAD) A. Koschik 21/22 W. Hofle / March 5, 2008 Extended LTC meeting

  22. Summary Damper essential to avoid increase of transverse emittance already in phase A (1-156 bunches) (shot-to-shot reproducibility with single bunch, kicker ripple effect with 43 to 156 bunches Damper commissioning can start from phase A1 with observation of signals Between now and first beam a lot of hardware commissioning, delay adjustments, calibrations in order to minimize time needed to get damper operational with beam Dedicated MD time required from phase A3 onwards (after RF capture) to set-up the system Injection damping available from phase A4 onwards Commissioning of abort gap cleaning from phase A5-A6 onwards (first 2 minutes of ramp) Commissioning damper during ramp in A7 to prepare for higher intensity of phase B Instability threshold expected to be hit in phase B Extended LTC meeting

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