Acknowledgements: P. Baudrenghien, A. Butterworth (AB/RF/CS), G. Kotzian, R. Louwerse,

1. LHC Transverse Damper Beam Commissioning Wolfgang HofleCERN AB/RF/FB Acknowledgements: P. Baudrenghien, A. Butterworth (AB/RF/CS), G. Kotzian, R. Louwerse, E. Montesinos (AB/RF/SR), V. Rossi, D. Valuch, V. Zhabitsky (for JINR / Dubna collaboration) LHC Commissioning Working Group

2. LHC Transverse Damper Beam Commissioning Outline • Overview of System, why do we need the damper on day ONE ? • Status of damper system – ongoing hardware commissioning • The different stages of initial commissioning with beam • Summary LHC Commissioning Working Group

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 LHC Commissioning Working Group

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 multiple excitations per cycle -> required for continuous tune measurement -> can be used to kick out unwanted beam (“abort gap cleaning”) -> making this mode operational requires software effort feedback: curing transverse coupled bunch instabilities -> will become important as intensity is raised, scrubbing in regime with e-cloud present LHC Commissioning Working Group

5. Injection kicker pulse with ripple (prototype) finite rise time kicker ripple injection kicker starts firing ~100 bunches in advance LHC Commissioning Working Group

6. Results of a simulation (kicker prototype waveform) beam blowup due to injection kicker imperfections and TFB OFF (red) [normalised rms in mm] 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 emittance blowup in previous SPS batch LHC Commissioning Working Group

7. Performance specification (1)(LHC Design Report) Beam parameters and requirements for nominal intensity: Injection beam momentum 450 GeV/c Static injection errors 2 mm (at bmax=183 m) ripple (up to 1 MHz) 2 mm (at bmax=183 m) resistive wall growth time 18.5 ms assumed de-coherence time 68 ms tolerable emittance growth 2.5 % Overall damping time 4.1 ms (46 turns) bunch spacing 25 ns minimum gap between batches 995 ns lowest betatron frequency > 2 kHz highest frequency to damp 20 MHz LHC Commissioning Working Group

8. Performance specification (2) Equipment performance specification: choice: “electrostatic kickers” (“base-band”) aperture 52 mm kickers per beam and plane 4 length per kicker 1.5 m nominal voltage up to 1 MHz at b=100m +/- 7.5 kV kick per turn at 450 GeV/c 2 mrad rise-time 10-90%, DV= +/- 7.5 kV 350 ns rise-time 1-99%, DV= +/- 7.5 kV 720 ns must provide sufficient gain from 1 kHz to 20 MHz noise must be less than quantization noise due to 10 bit / 2s rise time fast enough for gap of 38 missing bunches LHC Commissioning Working Group

9. 20 electrostatic kickers 40 wideband amplifiers, i.e. 40 tetrodes (RS2048 CJC, 30 kW) 20 amplifier cases H V H H H H V H H H V V V H V H V V V V The LHC Transverse Damping System (high power part) Damper system IP4 Beam 1 Beam 2 “Electrostatic” kicker Wideband amplifier Unit + Spare units Module LHC Commissioning Working Group

10. LHC optics at injection in IR4(beams do not cross!) Beam 1 high horizontal beta left of IP4 high vertical beta right of IP4 Beam 2 high horizontal beta right of IP4 high vertical beta left of IP4 Plots are Optics 6.4, sorry, 6.5 not very different for ADT) LHC Commissioning Working Group

11. Performance LHCADT performance in LHC optics version 6.500 compared to original assumptions (at 450 GeV/c), assuming 7.5 kV maximum kick voltage 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) LHC Commissioning Working Group

12. SR4 (surface): Signal Processing electronics (VME crates) HV Power Converters PLC controls 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 2 Beam 1 LHC Commissioning Working Group

13. Overview of one damper system low level Electronic (surface) kickers and power amplifiers (tunnel) controls amplification and interlocking (UX45, underground) pick-ups (tunnel) LHC Commissioning Working Group

14. Overview of signal processing hardware beam position VME module signal processing VME module LHC Commissioning Working Group

15. signal processing VME module (intelligence) LHC Commissioning Working Group

16. ^ • Frequency domain: maximum of transfer impedance ZT = 6.46 W @ 500 MHz Coupler Type Beam Position Monitor • Peak sensitivity: 0.264 W / mm => 8.1 V/mm peak in time domain after ideal hybrid • Peak voltage (beam centered) for ultimate beam @ collision: ~140 V -> very large LHC Commissioning Working Group

17. 8 Dedicated Pick-ups BPMC @ Q7L, Q7R, Q9L, Q9R 50 W couplers of 150 mm length on one end short circuited LHC Commissioning Working Group

18. Detection of bunch by bunch oscillations Simulation model enables to study imperfections of hardware and also propagate noise or interferences through system and evaluate their impact Bunch synchronous sampling with a 40 MHz clock rate LHC Commissioning Working Group

19. LHC Transverse Damper Beam Commissioning Outline • Overview of System, why do we need the damper on day ONE ? • Status of damper system – ongoing hardware commissioning • The different stages of the commissioning with beam • Summary LHC Commissioning Working Group

20. Status of Transverse Damper (1) Underground installation and Hardware Commissioning RB 44/46 (tunnel): Kickers installed, vacuum bake out OK Power amplifiers installed, tested, water cooling OK, final characteristics to be measured in situ Pick-ups @ Q7, Q9: installed, external cabling partially OK, loads to be installed for unused ports Equalization of cable lengths: Non-conformities to be followed-up UX45: 200 W driver amplifiers installed HOM loads from kickers installed PLC controls installed and tested Interlock crates installed and tested; calibration of power interlock to be done Signal observation crates: Not yet installed, cables to be pulled between racks LHC Commissioning Working Group

21. Assembly and Installation of kickers LHC Commissioning Working Group

22. Measured Characteristics of 16 installed amplifiers Actual performance between 10-20 MHz will be better than shown on graph -> calibrated measurements necessary to show real voltage on kickers (hardware commissioning) gain E. Montesinos (AB/RF/SR) for CERN-JINR collaboration frequency LHC Commissioning Working Group

23. Status of Transverse Damper (2) Surface installation and Hardware Commissioning (SR4) Power equipment: 8 power converters installed and commissioned (anode voltage for tetrode amplifiers) Full loading of 2x2 MW 18kV/400V transformers feeding damper power converters to be checked 48 smaller auxiliary power converters installed and commissioned (Ug1, Ug2 for tetrode amplifiers) PLC controls commissioned Lowlevel electronics for damper in SR4: Main cables pulled, crates installed Prototypes of beam position and signal processing modules hardware wise OK modifications to be implemented for series production FPGA code to be developed and tested for final boards Controls software to be defined and implemented LHC Commissioning Working Group

24. LHC Transverse Damper Beam Commissioning Outline • Overview of System, why do we need the damper on day ONE ? • Status of damper system – ongoing hardware commissioning • The different stages of the commissioning with beam • Summary LHC Commissioning Working Group

25. Beam Commissioning Phase A1 and A2First turn and circulating beam(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 LHC Commissioning Working Group

26. Beam Commissioning Phase A3(after RF capture) Commissioning RF front-end 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 Scan injection kicker pulse by moving bunch LHC Commissioning Working Group

27. 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 (low frequency) Make necessary adjustments (gain, phase, delay) Close damper loop Scan gain, phase, delay and measure damping time and stability limits Commission beam blow-up facility Measure beam lifetime as function of damper gain LHC Commissioning Working Group

28. Beam Commissioning Phase A6[first 2 minutes of ramp] Abort gap cleaning and machine Protection: Check machine protection interlocks, OK when damper goes crazy ? Try out abort gap cleaning techniques (this requires the collimators) Optimize abort gap cleaning programs LHC Commissioning Working Group

29. 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 LHC Commissioning Working Group

30. Summary Hardware commissioning of power system well advanced Lowlevel electronics prototypes OK Focus now shifting to final FPGA programming, testing and software Damper commissioning can start from phase A1 with observation of signals Damper essential to avoid increase of transverse emittance (kicker ripple effect when full batch) LHC Commissioning Working Group