BEAM TESTS OF THE LHC TRANSVERSE FEEDBACK SYSTEM

Transcription

1 JINR BEAM TESTS OF THE LHC TRANSVERSE FEEDBACK SYSTEM W.Höfle, G.Kotzian, E.Montesinos, M.Schokker, D.Valuch (CERN) V.M. Zhabitsky (JINR) XXII Russian Particle Accelerator Conference , Protvino

2 BE RF BEAM TESTS OF THE LHC TRANSVERSE FEEDBACK SYSTEM W.Höfle E.Montesinos D.Valuch. M.Schokker G.Kotzian RuPAC 21 2

3 LHC Beam Parameters Injection Collision Beam Data Proton energy [GeV] 45 7 Relativistic gamma Number of particles per bunch Number of bunches 288 Longitudinal emittance (4σ) [ev s] Transverse normalized emittance [μm rad] Circulating beam current [A].582 Stored energy per beam [MJ] Peak Luminosity Related Data RMS bunch length [cm] RMS beam size in ATLAS and CMS [μm] RMS beam size in ALICE and LHCb [μm] Geometric luminosity reduction factor F Peak luminosity for ATLAS and CMS [cm -2 s -1 ] RuPAC 21 3

4 JINR LHC Transverse Feedback System The LHC will provide high intensity proton and lead ion beams. The ultimate intensities after injection into the LHC will be about ( x 288 bunches) particles for the proton beam with an energy of 45 GeV, (7 1 7 x 592 bunches) ions for the 28 Pb 82+ beam with an energy of 177 GeV/u. These intensities can lead to coherent transverse instabilities. The theoretical prediction for the instability rise time τ inst, dominated by the resistive wall effect, is about 18.5 ms or 28 turns at injection energy for protons, and a significant contribution of the LHC collimators at collision energy to τ inst is also predicted. The LHC Damper will stabilize the beam against coupled bunch instabilities RuPAC 21 4

5 Emittance blow-up => The LHC Damper will stabilize the beam against coupled bunch instabilities as well as damp the transverse oscillations of the beam originating from steering errors and kicker ripple RuPAC 21 5

6 beam momentum & stored energy of colliders E beam = 362 MJ L.Evans. CHIPP APM Enough to melt 5 kg of copper Energy stored in the accelerator beam, as a function of beam momentum. At less than 1% of nominal intensity LHC enters new territory. Stored energy density as a function of beam momentum. Transverse energy density is a measure of damage potential and is proportional to luminosity RuPAC 21 6

7 JINR LHC Transverse Feedback System The LHC Damper will stabilize the beam against coupled bunch instabilities as well as damp the transverse oscillations of the beam originating from steering errors and kicker ripple. It will also be used for the purposes of tune measurement and for abort gap cleaning RuPAC 21 7

8 JINR LHC Transverse Feedback System Digital Signal Processor Front Electronics DK Delay Amplifier C T Q f t f rev RF b N H b m μs 64.28; Q RF rev.375 ns; f T V / K 1 /1 4 MHz; b 4 MHz 288; 1 b 25 ns (pilot beam) f BPM BPM RuPAC 21 8

9 JINR The LHC Damper Electro-static kickers base-band Integrated transverse electric field E ds (for 45 GeV/c) 9 kv per turn Aperture of kickers Number of kickers per beam and plane 4 Length electrodes in kicker Nominal voltage up to 1 MHz (at β = 1 m) 52 mm 1.5 m ±7.5 kv Kick per turn at 45 GeV/c (at β = 1 m) 2 µrad (.2 σ) Rise-time 1-9%, V max = ±7.5 kv Performance specification 35 ns Rise-time 1-99%, V max = ±7.5 kv 72 ns *) Frequency range for gain 1 khz 1 (2) MHz *) Rise time fast enough for gap of 38 missing bunches (9 ns for rise time (.5 %-99.5 %) in the LHC injection kicker ) RuPAC 21 9

10 JINR The LHC Damper Installation and Physical layout in Point 4 underground LHC ADT (4 modules) left of IP4 + space for 2 more modules (upgrade) ADT (4 modules) right of IP4 + space for 2 more modules (upgrade) RuPAC 21 1

11 JINR The LHC Damper Layout of the LHC Damper (four independent systems, one per plane (H/V) and beam) block-diagram of the transverse feedback system for vertical oscillations. The feedback loop contains all functionalities for transverse damping and controlled bunch excitation as well as many built-in features allowing the user full remote operation and diagnostics RuPAC 21 11

12 JINR The LHC Damper 7/8 inch coaxial cable (coaxial lines of m) Beam Position Monitor in Cryomodule RuPAC 21 12

13 The LHC Damper RuPAC 21 13

14 JINR The LHC Damper Pick-up Signal Processor Crate Comb Filter RuPAC 21 14

15 JINR The LHC Damper Beam Position Module Digital Signal Processor Unit RuPAC 21 15

16 JINR The LHC Damper The Thales Communications (Belgium) Front view Rear view 2 W solid state driver amplifier: 43 db gain, very flat, 3 khz 2 MHz RuPAC 21 16

17 JINR The LHC Damper CERN. 21 December 26. Electrostatic Kickers and Wideband Power Amplifiers in the LHC tunnel RuPAC 21 17

18 JINR The LHC Damper 5u Anode voltage 12KV Lemo 3KV 1 1u x 16kV 5 x 5W 1u x 16kV Monitor1 1:1 BNC 1 5 Water cooled Water cooled 5 1 BNC Monitor2 1:1 115p 115p Matching circuit 4x1k 1W U4 RS248-CJ 1n 16KV Deflector 1n 16KV U4 RS248-CJ 4x1k 1W Matching circuit N.I.Lebedev, Leading engineer. E.V.Gorbachev, Leading engineer. A.A.Makarov, Leading designer. Input1 Control grid bias2 22 Mains BNC 1 BNC 1 1u 5 From control circuit SW k 4u 8x75p 3KV 6x15 2W 6x15 2W 1n 1u 1u TX1 Filament Timer 6s K1 8x75p 3KV 6x15 2W 1u 4u 1.5KV 1k 2W 1u 1k 5 6x15 2W 1n 4u 1u TX2 Filament2 K2 SW From control circuit Timer 6s Lemo 5KV 1 Screen grid bias 1V BNC 1 Input2 1 BNC Control grid bias2 22 Mains R.A.Smolkov, Leading engineer. N.V.Pilyar, Leading engineer. Push-pull wideband power amplifier: Class of operation: AB Input amplitude: ±15 V Output amplitude: ±75 V Bandwidth: 1 khz 1 (2) MHz Power elements: two 3 kw Thales RS 248-CJC tetrodes RuPAC 21 18

19 Value of tolerance, mm JINR The LHC Damper S.Rabtsun. Leading Designer. Internal diameter D Required: +.54 mm (Ø1 mm),5,4,3,2, Tank N Parameter Surface smoothness (L K =1.6 m; Ø1 mm) Required / Achieved 1.6 μm /.4 μm The vacuum pressure values are between 8. x 1-1 and 1. x 1-9 mbar RuPAC 21 19

20 JINR The LHC Damper Parameter Required Achieved Lowest frequency 1 khz 1 khz Highest frequency 2 MHz 2 MHz Nominal - 3dB bandwidth 3 khz 1 MHz 2 khz -.95 MHz Nominal voltage at 1 MHz ±7.5 kv ±7.8 kv Gain, db Gain ripple ±.7 db ±.5 db Rise-time 1-9%, V max = 7.5 kv 35 ns 41 ns Rise-time 1-99%, V max = 7.5 kv 72 ns 76 ns The measured characteristics of the amplifier in the frequency range from 1 khz to 3 MHz correspond globally to the design specifications. The available peak voltage of 11 kv at 1 khz has exceeded the design value 1.5 kv RuPAC 21 2

21 JINR The LHC Damper First Beam Tests: 16 kickers (JINR) and front-electronics (CERN) were successfully checked for first beams in the LHC. Tune measurements with excitation (scanning) of the beam 2 (about protons in the single bunch) by kickers with power amplifiers of the LHC Damper. (23: September 28) Signals from the LHC Damper pick-up for the first shots: beam 1. 7 September 28. beam 2. 1 September RuPAC 21 21

22 Hardware Tuning Wideband Power Amplifiers: tetrodes rearrangement I a [A] 2, 1,5 1,,5, U g1 [V] I a [A] 2, 1,5 1,,5, Green curves = new situation. Red curves = previous tetrodes (removed) U g1 [V] RuPAC 21 22

23 Wideband Power Amplifiers: tetrodes rearrangement , 2, 2, 1, 1, 1,,,, , 2, 2, 2, 1, 1, 1, 1,,,,, All amplifiers now have similar pair of tetrodes for I a (U g1 ) characteristics RuPAC 21 23

24 Hardware Tuning RuPAC 21 24

25 Hardware Tuning Measurements of betatron phase advances between pick-ups Measured phase advances between pick-ups RuPAC 21 25

26 Beam Tests Single Bunch Operation: Damping of Injection Errors Damper OFF Damper ON RuPAC 21 26

27 Beam Tests Single Bunch Operation: Damping of Injection Errors Damper OFF Damper ON for horizontal oscillations RuPAC 21 27

28 Beam Tests Single Bunch Operation (45 GeV): Damping of Vertical Oscillations induced by the Q-kicker High Gain Lower Gain RuPAC 21 28

29 Beam Tests Single Bunch Operation (3.5 TeV): Damping of Transverse Oscillations induced by the Q-kicker RuPAC 21 29

30 LHC Damper: Emittances Beam / plane ε n, / 7:47 B1H 2.4 B1V 2.8 B2H 2.7 B2V / 22:3 : Test ramp with orbit FB and transverse damper on B2 V plane damper on (at low gain) in the ramp (3.5 TeV) RuPAC 21 3

31 Beam Size evolution 5 6 May 21 Damper on RuPAC 21 31

32 The LHC Damper 15 ns Bunch Train Operation The LHC Damper specification: < protons per bunch of length >1 ns at a saturation of ±2 mm an amplitude resolution of about 1 μm RuPAC 21 32

33 Pilot ramp Damper functions at injection-ramp damper gain 45 GeV (-6 db B1HV / -12 db B2V) 3.5 TeV on (-5 db B1HV / -11 db B2V) maintain damping time in ramp (exact function to be calculated) Max. gain for hump dumping Q-FB on (-22 db B1HV / -28 db B2V) cycle time RuPAC 21 33

34 Abort Gap Cleaning Cleaning pulse shape used in 29 beam tests RuPAC 21 34

35 Abort Gap Cleaning EXPERIMENTAL RESULTS: December 29 Cleaning of a coasting beam: - 4 bunches of protons - RF switched off - After 5 minutes, started cleaning using stepped frequencies around Q v Beam dumped gap had not been completely emptied. RF off cleaning starts synchrotron light production decreased proportionally to the gap population gap population equilibrium Abort Gap Monitor signal during coasting beam cleaning experiment. T.Lefevre et al. First Operation of the Abort Gap Monitors for LHC. IPAC-21, May 21, Kyoto, Japan, pp RuPAC 21 35

36 Abort Gap Cleaning ; V4.B2 (#16) W.Hofle & D.Valuch Abort gap cleaning pulse (full steam) switching matrix left without phase compensation, right with phase compensation red trace: non-active tube, olive: active tube, yellow: difference 2 us window 3 khz (gives the slope at flat top) RuPAC 21 36

37 CONCLUSIONS Beam tests and commissioning of the LHC transverse feedback system have been successfully completed. All of the 16 damper kickers, 16 wideband power amplifiers and 8 low-level subsystems have been operating continuously since. The LHC Damper is now routinely used during injection, ramping and collisions for active damping RuPAC 21 37

38 CERN T.Linnecar V.P. Sarantsev, I.N. Ivanov, 1991 D.Boussard JINR RuPAC 21 38