0
play

0 1 Update on Beam Tests with PS Finemet Cavity H. Damerau, L. - PowerPoint PPT Presentation

Jun 04, 2023 •208 likes •534 views

0 1 Update on Beam Tests with PS Finemet Cavity H. Damerau, L. Ventura LIU-PS Working Group Meeting June 9, 2015 Many thanks to Matthias Haase and Mauro Paoluzzi 2 Overview Introduction Coupled-bunch feedback Beam-loading

  1. 0

  2. 1 Update on Beam Tests with PS Finemet Cavity H. Damerau, L. Ventura LIU-PS Working Group Meeting June 9, 2015 Many thanks to Matthias Haase and Mauro Paoluzzi

  3. 2 Overview • Introduction • Coupled-bunch feedback • Beam-loading compensation feedback • Low intensity and high intensity, triple splitting • Excitation of coupled-bunch oscillations • Mode scans • Excitation rates • Summary and outlook

  4. 3 Introduction • LS1: - New Finemet cavity installed in SS02 (M. Paoluzzi et al.) • 2014: - First cavity gap available for test with LLRF system - Tests of beam-loading compensation feedback - 12 harmonics damped with nominal intensity LHC25ns • 2015: - 3 gaps available, 4 gaps after June technical stop - Excitation of coupled-bunch instabilities in open loop - Measurement of excitation amplitudes vs. cavity voltage

  5. 4 Overview • Introduction • Coupled-bunch feedback • Beam-loading compensation feedback • Low intensity and high intensity, triple splitting • Excitation of coupled-bunch oscillations • Mode scans • Excitation rates • Summary and outlook

  6. 5 Beam-loading compensation (1 harmonic) sin( h FB f rev t + f) sin( h FB f rev t ) Low-pass Cavity Cavity ADC DAC return drive Low-pass cos( h FB f rev t ) cos( h FB f rev t + f) cos(( h RF - h FB ) f rev t + f) f s side- Wall band filter current ADC monitor f s side- band filter sin(( h RF - h FB ) f rev t + f)

  7. 6 First measurements with beam in 2014 • Moderate feedback gain Open/closed loop transfer function (very first test!) • Transfer function measurement: ~ 10…12 dB • Spectrum of beam induced voltage in Finemet cavity • 26GeV-test cycle, low intensity single bunch 500 kHz 6 MHz accelerated on h = 8  Impedance reduction observed with beam as expected

  8. 7 High-intensity, 6/7 filling, triple splitting • First 12 harmonics simultaneously  1 bunch for nominal LHC25ns beam injected from PSB  6 bunch with nominal intensity for LHC25ns injected  15…20 dB reduction of beam induced voltage, also during triple splitting

  9. 8 Overview • Introduction • Coupled-bunch feedback • Beam-loading compensation feedback • Low intensity and high intensity, triple splitting • Excitation of coupled-bunch oscillations • Mode scans • Excitation rates • Summary and outlook

  10. 9 Coupled-bunch oscillations, freq. domain F. Pedersen, F. Sacherer, PAC77, pp. 1397-1399  Synchrotron frequency sidebands of the f rev harmonics:  In the case of LHC-type beams in the PS ( h = 21) upper lower

  11. 10 Beam excitation with the Finemet cavity sin( h FB f rev t + f) sin( h FB f rev t ) Low-pass Cavity Cavity ADC DAC return drive Low-pass cos( h FB f rev t ) cos( h FB f rev t + f) Amplitude Excitation frequency, D f D f sin Low freq. f DDS h FB f rev cos  Excitation frequency ~ f s Side-band selection away from hf rev Amplitude  ~ 400 Hz at 476 kHz

  12. 11 First excitation test using Finemet cavity • Observe beam stability during acceleration after transition No excitation, gaps open Excitation at exactly 20 f rev  No effect with voltage from Finemet cavity at f rev harmonic

  13. 12 First excitation test using Finemet cavity • Frequency offset of ~ 300 Hz at start of excitation Excitation, D f = + 300 Hz Excitation, D f = - 300 Hz  Strong excitation with frequency offset with respect to 20 f rev  Beam qualitatively behaves as expected

  14. 13 Overview • Introduction • Coupled-bunch feedback • Beam-loading compensation feedback • Low intensity and high intensity, triple splitting • Excitation of coupled-bunch oscillations • Mode scans • Excitation rates • Summary and outlook

  15. 14 Mode scan measurements LHC25 ns beam with ~1.3  10 11 ppb equivalent intensity • • 4+2 and 4+3 bunches (full ring) injected from PSB g tr or Start excitation • L. Ventura Two independent mode analysis techniques:

  16. 15 Mode scan with 18 bunches in h = 21, cavity 11 Data with old coupled bunch feedback  Some modes can be excited very cleanly, others as a mixture; artefact?

  17. 16 Mode scan with 18 bunches in h = 21, Finemet New coupled-bunch feedback LLRF, excitation of each mode  All 18 modes can be excited

  18. 17 Mode scan with 21 bunches in h = 21, cavity 11 Excite each mode individually and measure mode spectrum  Clean observation of all possible modes

  19. 18 Mode scan with 21 bunches in h = 21, Finemet New coupled-bunch feedback LLRF, excitation of each mode Upper side-band: n = n exc Lower side-band: n = 21 - n exc  Every oscillation mode from n = 1…21 can be excited on both side -bands

  20. 19 Overview • Introduction • Coupled-bunch feedback • Beam-loading compensation feedback • Low intensity and high intensity, triple splitting • Excitation of coupled-bunch oscillations • Mode scans • Excitation rates • Summary and outlook

  21. 20 Excitation amplitude scan Vary excitation amplitude and check mode spectrum ~20 ms after excitation starts: Upper sideband of f rev Lower sideband of f rev  Oscillation amplitude proportional to excitation  linear regime  Mode amplitudes comparable to excitation with spare cavity C10-11 • Absolute excitation voltages to be analyzed

  22. 21 Growth of coupled-bunch oscillation Mode amplitude versus time: two measurement techniques Down-converted sidebands at 20 f rev Oscillation amplitude from mode analysis Signal around 20 f rev L. Ventura ~ 38 ms V RF Finemet cav. 40 ms  Both measurement techniques give very similar results  Growth not exponential • How to derive growth times?

  23. 22 Growth of coupled-bunch oscillation Mode amplitude versus time: two measurement techniques Down-converted sidebands at 20 f rev Driven harmonic oscillator model Signal around 20 f rev V RF Finemet cav. 40 ms  Both measurement techniques give very similar results  Growth not exponential • How to derive growth times? • Driven harmonic oscillator model?

  24. 23 Overview • Introduction • Coupled-bunch feedback • Beam-loading compensation feedback • Low intensity and high intensity, triple splitting • Excitation of coupled-bunch oscillations • Mode scans • Excitation rates • Summary and outlook

  25. 24 Summary • Beam induced voltage reduction tests  12 harmonic damped simultaneously with up to 20 dB gain  Nominal intensity of 25 ns beam, follows RF manipulations • First tests without and with beam successful  Coupled-bunch oscillations excited as expected  Each mode can be excited individually  Confirms measurements with C10-11 in 2013  Qualitatively: Finemet cavity touches beam as expected  Quantitatively: More measurements/analysis needed

  26. 25 Outlook • Future MDs to complete excitation measurements  Scan excitation amplitude and frequency offset  Derive growth/damping rates for given cavity voltage  Check with shorter bunches (50 ns-like beam)  Excite multiple modes simultaneously  Excite quadrupolar oscillation modes • Follow-up firmware development  Complete filter design for synchrotron frequency side-bands  Close the loop on one harmonic

  27. 26 26 THANK YOU FOR YOUR ATTENTION!

  28. 27 Operational PS coupled-bunch feedback div/Meetings/APC/2005/apc050609/JL_Vallet_slides.pdf J.-L. Vallet, https://ab-div.web.cern.ch/ab- • Analogue signal processing, two channels Two accelerating cavities as feedback kickers  limits to modes h – 1 and h - 2 •  New wide-band Finemet cavity as kicker Cover all modes  Digital feedback electronics

  29. 28 New cavity (#25) in the PS ring • Wide-band (0.4 – >5.5 MHz, V RF = 5 kV) cavity based on Finemet material • No acceleration, but damping of coupled-bunch oscillations SS02 6-cell cavity unit G F Accelerating gap Power amplifiers M. Paoluzzi (solid state) • Cavity installed in SS02, amplifiers on 2 gaps  First installation of transistor power amplifiers close to beam in PS

  30. 29 Damping rate versus gain and intensity Versus gain Measured damping rate with feedback on Corrected for natural damping  Zero damping at zero gain  Natural damping in- dependent from gain Versus intensity  Damping increases with intensity, more signal for given CB oscillation amplitude ‐ Saturation leads to non- zero damping with zero N p ?

  31. Damping rate versus e l and cycle time 30 Versus e l (RMS)  Uncorrected: damping efficiency increases for larger e l  Reduced natural stability for smaller e l  Corrected damping independent from e l During cycle ~26 GeV ~26 GeV  Damping efficiency reduces at higher ~9 GeV energy ~9 GeV  To be checked with simulations

  32. 31 Kick voltage versus oscillation amplitude • Excite a coupled-bunch oscillation and measure its amplitude • Observe maximum damping voltage required • Only order of magnitude for kick voltage  Overestimate expected as feedback normally started before oscillations are well developed Basic specifications of kicker Frequency range 0.4 to 5.5 MHz cavity: RF voltage per sideband, V mode ~ 1 kV Maximum total RF voltage, V max ~ 5 kV M. Paoluzzi, H.D., < 200 W Un-damped shunt impedance at n · f rev CERN-ACC-NOTE-2013-0019

Recommend

More recommend