1. W. Hofle / March 5, 2008 Extended LTC meeting 1/22 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) Wolfgang Hofle CERN AB/RF/FB LHC Transverse Damper Beam Commissioning

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

3. W. Hofle / March 5, 2008 Extended LTC meeting 3/22 Pick-up 1 Kicker Signal processing  beam  signal Pick-up 2  gain g 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 feedback: curing transverse coupled bunch instabilities excitation: of transverse oscillations for beam measurements & other applications damping: of transverse injection oscillations Transverse multi bunch feedback principle

4. W. Hofle / March 5, 2008 Extended LTC meeting 4/22 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 ! 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 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) Why do we need Transverse damper on day ONE ?

5. W. Hofle / March 5, 2008 Extended LTC meeting 5/22 where  dec de-coherence time in absence of instability and active damping  inst instability rise-time  ad active damping time as it would follow from damper gain without having any instability and without de-coherence phenomena and assuming  dec >>   nst >  ad the emittance increase becomes without damper a steering / kick error of  x in position and  x’ in angle will lead to a relative emittance increase of Introducing the effective (overall) damping rate Reminder: Emittance increase by filamentation typically  dec > 10 x  ad hence emittance increase reduced by factor >100 ! -> justifies having damper from start blow-up reduction factor

6. W. Hofle / March 5, 2008 Extended LTC meeting 6/23 Injection kicker pulse with ripple (prototype) kicker ripple finite rise time Scanning with single bunch suggested in phase A4 to verify effective kick seen by beam (see talk by V. Kain) Bunch positions for 43 bunch filling pattern 243/3564=0.0682 or 6075 ns

7. W. Hofle / March 5, 2008 Extended LTC meeting 7/23 Results of a simulation (kicker prototype waveform) emittance blowup in previous SPS batch beam blowup due to injection kicker imperfections and TFB OFF (red) beam emittance with TFB ON (black)  within design parameters (3.75um) G. Kotzian, simulations ongoing, new kicker waveforms from AB-BT for actual kickers need to be included [normalised rms in  m] bunch positions for 43 bunch filling pattern (4 bunches injected) batch length 243x25 ns, e.g. pos. 650->893 batch length for 156 bunch scheme is 315 bunch positions (16 bunches), longer than nominal batch of 25 ns operation (311 positions)

8. W. Hofle / March 5, 2008 Extended LTC meeting 8/22 LHC Commissioning phase A: 1 to 156 bunches 1)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 2)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 Reminder: filling patterns, kicker ripple and transverse feedback 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

9. W. Hofle / March 5, 2008 Extended LTC meeting 9/22 Outline LHC Transverse Damper Beam Commissioning  Overview of System, why do we need the damper on day ONE ?  Readiness for beam commissioning stages of the commissioning with beam  Summary

10. W. Hofle / March 5, 2008 Extended LTC meeting 10/22 The LHC Transverse Damping System (high power part)  20 kickers  40 wideband amplifiers, i.e. 40 tetrodes (RS2048 CJC, 30 kW) 20 amplifier cases Damper system Beam 1 IP4 damper kicker Beam 2 Wideband amplifier Unit HHVV HHHH VVVV HHHH VVVV Module Installed, hardware commissioning under way calibrations and phasing still need to be completed, quite some work for AB/RF group Status of installation and hardware commissioning: see talk by Olivier Brunner on Tuesday

11. W. Hofle / March 5, 2008 Extended LTC meeting 11/22 Overview of one damper system (there are four, one per beam and plane) pick-ups (tunnel) kickers and power amplifiers (tunnel) low level electronics (surface) controls amplification and interlocking (UX45, underground) phase A2: put excitation on beam to verify kick strength phase A1, A2 does not require capture signal levels, phasing (delay) feedback loop start commissioning in phase A3 close loop in phase A4: requires RF capture

12. W. Hofle / March 5, 2008 Extended LTC meeting 12/22 Beam Commissioning Phase A1 and A2 First 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)

13. W. Hofle / March 5, 2008 Extended LTC meeting 13/22 beam position VME module signal processing VME module DSPU (“Damper Loop”) based on 1T-FB module Overview of signal processing prototypes exist, firmware (FPGA) being developed not static, i.e. evolution of firmware to incorporate additional functionalities, upgrades, optimizations commission in A3 commission in A4 intensity nomalised bunch position digitised and synchronised (two pick-ups)

14. W. Hofle / March 5, 2008 Extended LTC meeting 14/22 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 f rev 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 ?

15. W. Hofle / March 5, 2008 Extended LTC meeting 15/22 signal processing VME module (DSPU, “damper loop”) based on 1T-FB module Input: nomalised bunch position synchronised (two pick-ups) commission in A4 scaling:  -functions Phase shifter optional not needed on day 1 FGC control “phase”, two functions FGC control “delay” FGC control “gain” 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)

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

17. W. Hofle / March 5, 2008 Extended LTC meeting 17/22 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

18. W. Hofle / March 5, 2008 Extended LTC meeting 18/22 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

19. W. Hofle / March 5, 2008 Extended LTC meeting 19/22 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 …

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

21. 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 Simulations (MAD) A. Koschik abort gap cleaning in LHC using transverse damper Extended LTC meeting W. Hofle / March 5, 2008 21/22 compare with MDs as early as possible

22. W. Hofle / March 5, 2008 Extended LTC meeting 22/22 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 Summary

23. W. Hofle / March 5, 2008 Extended LTC meeting 23/27 ADT racks (driver amplifiers, PLC controls, fast interlocks) ADT (4 modules) left of IP4 + space for 2 more modules (upgrade) ADT (4 modules) right of IP4 + space for 2 more modules (upgrade) Beam 1 Beam 2 SR4 (surface): Signal Processing electronics (VME crates) HV Power Converters PLC controls Additional Slides – Underground Layout

24. W. Hofle / March 5, 2008 Extended LTC meeting 24/27 Performance specification (1) (LHC Design Report) Beam parameters and requirements for nominal intensity: Injection beam momentum450 GeV/c Static injection errors 2 mm (at  max =183 m) ripple (up to 1 MHz) 2 mm (at  max =183 m) resistive wall growth time18.5 ms assumed de-coherence time68 ms tolerable emittance growth2.5 % Overall damping time4.1 ms (46 turns) bunch spacing25 ns minimum gap between batches995 ns lowest betatron frequency> 2 kHz highest frequency to damp20 MHz Additional Slide – Performance Specification

25. W. Hofle / March 5, 2008 Extended LTC meeting 25/27 Performance specification (2) Equipment performance specification: choice:“electrostatic kickers” (“base-band”) aperture52 mm kickers per beam and plane4 length per kicker1.5 m nominal voltage up to 1 MHz at b=100m+/- 7.5 kV kick per turn at 450 GeV/c2  rad rise-time 10-90%,  V= +/- 7.5 kV350 ns rise-time 1-99%,  V= +/- 7.5 kV720 ns must provide sufficient gain from 1 kHz to 20 MHz noise must be less than quantization noise due to 10 bit / 2  rise time fast enough for gap of 38 missing bunches Additional Slide – Performance Specification

26. W. Hofle / March 5, 2008 Extended LTC meeting 26/27 E. Montesinos (AB/RF/SR) for CERN-JINR collaboration Actual performance between 10-20 MHz will be better than shown on graph -> calibrated measurements necessary to show real voltage on kickers (hardware commissioning) frequency gain Additional Slide – Measured characteristics of 16 installed amplifiers

27. W. Hofle / March 5, 2008 Extended LTC meeting 27/27 Performance LHCADT performance in LHC optics version 6.500 compared to original assumptions (at 450 GeV/c), assuming 7.5 kV maximum kick voltage  =100 m performance Optics 6.500 performance Kick per turn in  Kick per turn in  @  in m ADTH beam 1 0.2  0.271  at  =183 m ADTH beam 2 0.2  0.274  at  =189 m ADTV beam 1 0.2  0.301  at  =227 m ADTV beam 2 0.2  0.331  at  =275 m Estimate of maximum capabilities (usage as beam exciter, abort gap cleaning etc.), assumes optics 6.5 as in table above, 450 GeV/c and 7 TeV and running with up to ~15 kV DC for tetrode anode voltage (at 1 MHz 1.4x nominal) 100 kHz 1 MHz10 MHz20 MHz ADTH 0.42  0.11  0.38  0.10  0.12  0.03  0.044  0.011  ADTV 0.46  0.12  0.42  0.12  0.14  0.04  0.049  0.012  Additional Slide – Expected Performance (optics 6.500)