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Acknowledgements: P. Baudrenghien, G. Kotzian, V. Rossi, D. Stellfeld, D. Valuch

LHC Transverse Damper Electronics and Noise Analysis of Transverse Feedback System. Wolfgang Hofle CERN AB/RF/FB. Acknowledgements: P. Baudrenghien, G. Kotzian, V. Rossi, D. Stellfeld, D. Valuch. Noise Analysis of Transverse Feedback System. General choices and strip line pick-up.

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Acknowledgements: P. Baudrenghien, G. Kotzian, V. Rossi, D. Stellfeld, D. Valuch

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  1. LHC Transverse Damper Electronics and Noise Analysis of Transverse Feedback System Wolfgang HofleCERN AB/RF/FB Acknowledgements: P. Baudrenghien, G. Kotzian, V. Rossi, D. Stellfeld, D. Valuch LHC MAC - December 8, 2006

  2. Noise Analysis of Transverse Feedback System • General choices and strip line pick-up • Beam Spectrum and Signal Power from Pick-up • Expected noise performance for LHC transverse feedback • Possible upgrades for better S/N performance • Conclusions LHC MAC - December 8, 2006

  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 MAC - December 8, 2006

  4. Overview of one ADT System Choice: Digital electronics on surface -> easy access ! Installed or under assembly & installation LHC MAC - December 8, 2006

  5. LHC ADT Low-level Electronics • System will be based on experience gained with SPS Damper • Two coupler type pick-ups with betatron phase advance of ~90 degrees will be used (BPMC/BPMCA, provided by the BI group and integrated in quad) • Spectrum repeats every 40 MHz (25 ns bunch spacing) -> analogue down conversion with a multiple of 40 MHz to base band , LO of 400 MHz chosen • One of the horizontal pick-ups is installed at ~zero dispersion and it will be possible to use this pick-up and a Hilbert transformer (FIR filter) for the phase adjustment if wanted; Hilbert filter tested in SPS but not used in operation (reduced phase stability margin at very high gain) • FPGA technology for implementing most of the functions digitally (notch filter, fine delay adjustment, betatron phase adjustment by two pick-ups or Hilbert filter and single pick-up use) LHC MAC - December 8, 2006

  6. 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 MAC - December 8, 2006

  7. BPMC - Coupler type pick-ups 8 Dedicated Pick-ups BPMC @ Q7L, Q7R, Q9L, Q9R 50 W couplers of 150 mm length on one end short circuited LHC MAC - December 8, 2006

  8. BPMC - Coupler type pick-ups t Frequency Domain t = 2 L/c ~ 1 ns |ZT (w)| ^ ZT = 6.46 W Beam L=150 mm … w 500 MHz ^ ZT (w) = ZT j sin(wt/2) e -jwt/2 • Length of electrodes 150 mm ^ • Frequency domain: maximum of transfer impedance ZT = 6.46 W @ 500 MHz • Peak voltage (beam centered) for ultimate beam @ collision: ~140 V -> very large • Peak sensitivity: 0.264 W / mm => 8.1 V/mm peak in time domain after ideal hybrid LHC MAC - December 8, 2006

  9. Realistic simulation model is being developed to include actual characteristics of hardware Cable (650 m for Q9) BPM BP IQ demod RF=400.8 MHz Bunch synchronous sampling @ 40 MHz and digitization with 16 bit normalization (D/S) after calculation of sqrt(I*I+Q*Q) in digital part G. Kotzian LHC MAC - December 8, 2006

  10. Order of elements: Cable, hybrid, band pass 1st option: cable, hybrid, band pass sensitive to relative delay changes on the two cables special cables have been installed with low dependence of electrical length on temperature; measurements are being done during the winter and spring months to monitor the variations 2nd option: band pass, hybrid, cable need two well matched (identical) band pass filters; check when series production becomes available (preferred if filters OK) 3rd option: hybrid, cable, band pass need hybrid that can handle 140 V peak; possibly addition of a low pass filter before hybrid to reduce peak amplitude somewhat; being looked at; standard H9 hybrid can only handle 50 V peak (25 W) LHC MAC - December 8, 2006

  11. Simulations using simulink/matlab Some simulation results, single bunch Signal from pick-up Base band signal S after LP Base band D signal after LP Response of BP filter to D signal from pick-up G. Kotzian LHC MAC - December 8, 2006

  12. Simulations using simulink/matlab Simulation results, bunch to bunch oscillations Simulation model enables us 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 G. Kotzian LHC MAC - December 8, 2006

  13. Band pass filter prototypes (1) input output D. Valuch LHC MAC - December 8, 2006

  14. Band pass filter prototypes (2) 400 MHz prototype band pass filters built “Sampled line” type comb filter 8 dB attenuation @ 400 MHz achieved “Delay line” type comb filter 1 dB attenuation @ 400 MHz achieved D. Valuch LHC MAC - December 8, 2006

  15. Beam position front-end (two boards, analogue/ digital part) prototypes in production D. Valuch LHC MAC - December 8, 2006

  16. Digital Processing Board Digital Processing Module, two 1T FB boards received under test Reuse a modified version of this RF 1TF FB board for the TFB AD conversion will now be on Beam Position Front-end for TFB V. Rossi LHC MAC - December 8, 2006

  17. Signal levels from coupler type pick-ups • Length of electrodes 150 mm • Frequency domain: maximum of transfer impedance 6.46 W @ 500 MHz • Peak voltage for ultimate beam @ collision: ~140 V -> very large • Maximum of sensitivity at 500 MHz: 0.264 W/mm => 8.1 V/mm peak in time domain after ideal hybrid for ultimate beam [140 V x 21/2 / 24.5 mm] • install hybrid on surface (16.3 dB cable attenuation for Q9 will avoid saturation) -> peak voltage reduced from 140 V to ~21 V, OK for wideband hybrid H9 (25 W max) • Hybrid: 2 dB (+3 dB -1 dB) • after filtering: ultimate beam: ~0.38 V/mm @ 400 MHz; nominal 0.26 V/mm (duty cycle 0.8), to be checked with simulations LHC MAC - December 8, 2006

  18. Signal levels from pick-up LHC Beam Parameters ^ Range of intensities for LHC beam and expected pick-up signal levels (ZT = 3.23 W; ZT (w) = 6.46 W) Intensity range to be covered: factor 50 LHC MAC - December 8, 2006

  19. Aim at a better than 1 mm resolution • Assume bunches oscillate with 1 mm rms (bunch-to-bunch) • Power available from pick-up @400 MHz (+/- 20 MHz): 433 pW (nominal beam) to be checked • Thermal noise at 290 K: kBT = 4x10-21 W/Hz; in 40 MHz BW: 0.16 pW • Digitization with effective 14 bit: 16384 discrete levels, assume 1 mm -> 4 steps then 14 bit are sufficient to cover +/- 2 mm • Large margin with respect to thermal noise: To use this margin we should limit orbit variations at the pick-ups to less than +/- 2 mm. LHC MAC - December 8, 2006

  20. LHC ADT upgrade possibilities to improve on S/N • Digitization of pick-up signals underground -> save ~600 m of cable -> gain >12 dB (factor 4), but need to develop hybrids, filters and electronics to process large amplitude signals; alternatively use 1 5/8” cable: gain ~6 dB (factor 2) • If limited by interference & noise on link from surface to tunnel (3 kHz- 20 MHz) -> built digital link and have Digital-to-Analogue conversion as close as possible to amplifiers (possibly find new space for driver amplifiers that are now in UX45) • Increase beta functions at pick-ups (not very likely but worth a thought since otherwise no additional cost); in particular vertical beta function at BPMC.7L4.B2 for beam 2 somewhat low in optics version 6.5 (= 87 m) • Average in the signal processing over several turns, i.e. 9 turns, gain of a factor 3 in S/N if noise turn-by-turn uncorrelated - more turns not feasible due to limited signal processing power and sensitivity to tune. • Use additional pick-ups; strip-line pick-ups at Q8 and Q10 may be available; gain in S/N 50%, additional cables and electronics must be installed; further improvement by installing additional pick-ups, spread around the ring? LHC MAC - December 8, 2006

  21. Simulations to predict blow-up ongoing Effect of noise on beam: we are in contact with K. Ohmi (KEK) who is doing simulations on blow-up for LHC and LHC upgrades. He includes noise from the damper LHC MAC - December 8, 2006

  22. Conclusions • Signal Processing hardware in prototype production / testing • Need to continue simulations to evaluate performance • We aim to achieve a noise level of less than 1 mm rms oscillation detection. LHC MAC - December 8, 2006

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