Base-Band Tune (BBQ) Measurement System Marek Gasior Beam Instrumentation Group, CERN

1. Base-Band Tune(BBQ)Measurement SystemMarek GasiorBeam Instrumentation Group, CERN Base-Band Tune (BBQ) Measurement System

2. Tune measurement – The principle • Beam oscillations are observed on a position pick-up • Oscillations of individual particles are incoherent – an excitation needed for “synchronization” • Small beam oscillation signals in the presence of large revolution frequency content due to the fact that each bunch appears in the pick-up only once per revolution • Oscillations are usually observed in the frequency domain (separation from the strong background) Base-Band Tune (BBQ) Measurement System

3. Tune measurement – Classical approach • Linear processing of position pick-up signals • Dynamic range problems: revolution frequency content is large with respect to the betatron content • large kicks required • accurate gain control needed (signal cannot be clamped) • If only small kicks are affordable (to limit beam emittance blow-up), complicated solutions needed. e.g. • resonant pick-up (does not work with single bunches) • beam centering (mechanics or electronics), the limit is the hybrid Base-Band Tune (BBQ) Measurement System

4. 3 dB Classical approach – “One betatron harmonic filtering” • The LHC bunch length (4) is about 1 ns and the corresponding bunch spectrum cut-off is about 500 MHz • With just one bunch in the machine the revolution spectral lines are spaced by 11 kHz, so there are some 50 000 of these and some 100 000 betatron lines • When using the classical “one betatron harmonic filtering” method, one observes only 0.00001 (-100 dB) of the spectral content • This results in very small signals, requiring low noise amplifiers and mixers, which have small dynamic ranges; they can be easily saturated by a huge revolution content Base-Band Tune (BBQ) Measurement System

5. Tune measurement – Direct Diode Detection (3D) • Peak detection of position pick-up electrode signals (“collecting just the cream”) • frev content converted to the DC and removed by series capacitors • fb modulation moved to a low frequency range (as after the diodes fb is on much longer pulses) • A GHz range before the diodes, after the diodes processing in the a kHz range • Large sensitivity • Works with any position pick-up • Impossible to saturate (large frev suppression already at the detectors + large dynamic range) • Low frequency operation after the diodes • High resolution ADCs available • Signal conditioning / processing is easy (powerful components for low frequencies) Base-Band Tune (BBQ) Measurement System

6. sd(t) Electrode 1 signal Electrode 2 signal Signals of both peak detectors Detector signal difference Direct Diode Detection – The principle beam relative offset =0.1 betatron oscillation relative amplitude = 0.05 simulated tune value q=0.1 filter time constant = 10T (T – revolution period) storage capacitor Cf =Cpu (PU electrode capacitance) Base-Band Tune (BBQ) Measurement System

7. =100T 4 bunches   = 100 T Direct Diode Detection – The principle Signals of both peak detectors Detector signal difference =0,  = 0.01 q=0.1, Cf =Cpu =T Base-Band Tune (BBQ) Measurement System

8. Signals of both peak detectors Detector signal difference =0,  = 0.01 q=0.1, Cf =Cpu 4 bunches   = 100 T beamnot centered one bunch10 % larger Direct Diode Detection – Diodes not perfect Base-Band Tune (BBQ) Measurement System

9. q 0.5 q 0.5 Direct Diode Detection – Base band spectrum Base-Band Tune (BBQ) Measurement System

10. Architecture of the Base Band Q (BBQ) Measurement System Detector box (for one PU electrode) Analog front-end box (2 channels) Base-Band Tune (BBQ) Measurement System

11. BBQ systems at CERN LHC, SPS PS, PSB, LEIR • BBQ system operational at RHIC • Tested at Tevatron • Will be operational at the CNAO hadrontherapy machine Base-Band Tune (BBQ) Measurement System

12. SPS BBQ Base-Band Tune (BBQ) Measurement System

13. SPS BBQ – Transverse damper noise • 1 bunch LHC pilot, • 5109 p+, 26-450 GeV Damper system OFF Damper system ON No explicit beam excitation Base-Band Tune (BBQ) Measurement System

14. (no filters) SPS BBQ – Low-pass filtering • Measurement with the fixed target beam (a few thousand small bunches), no excitation • BOSC – a homodyne tune measurement system • A low-pass filter before the diodes cleans up the bunch longitudinal shape • Important beam noise filtering at a small expense of a few dB signal loss, resulting in an important SNR improvement • Similar effects seen on the PS and PSB Base-Band Tune (BBQ) Measurement System

15. PS EASTB, regular kick every 10 ms TOF, regular kick every 10 ms Base-Band Tune (BBQ) Measurement System

16. PSB LHC25A, R3, no kick Same, kick 20 V (a % of the standard kick) Base-Band Tune (BBQ) Measurement System

17. LEIR NOMINAL, regular kick 500 V, every 10 ms Same, no kick Base-Band Tune (BBQ) Measurement System

18. (Sound card) Record of the RHIC BBQ signals Horizontal plane (L) injections ramp squeeze RF switching Q' too small Vertical plane (R) about 10 minutes Base-Band Tune (BBQ) Measurement System

19. Spectra of the RHIC BBQ signals Hor. Ver. Base-Band Tune (BBQ) Measurement System

20. Store beginning 5 hours later (end of the store) H plane H plane V plane V plane RHIC BBQ measurements – Collisions Base-Band Tune (BBQ) Measurement System

21. Conclusions BBQ advantages Sensitivity (noise floor in the nm range for intense beams) • Simplicity and low cost • no timing, no resonant PU, no movable PU, no hybrid, no mixers, it can work with any PU • Very robust for saturation • Base band processing and acquisition • excellent 24 bit audio ADCs available • Signal conditioning / processing is easy (powerful components for low frequencies) • Independence of the machine filling pattern • Flattening out of the beam dynamic range (small sensitivity to number of bunches) BBQ disadvantages • Interference: operation in the low frequency range • It is sensitive to the "bunch majority“(gating needed to measure separate bunches) Future development • Gating a bunch or a group of bunches(successful proof of principle done with beam) • Continuous head-tail chromaticity measurement(tests with beam and some theoretical studies done) Base-Band Tune (BBQ) Measurement System

22. =100T Extra slides: Direct Diode Detection – SNR limits Base-Band Tune (BBQ) Measurement System

23. AD SFTPRO TOF Extra slides: PS BBQ – Detector DC voltages Base-Band Tune (BBQ) Measurement System

24. Extra slides: RHIC BBQ – Tune scan Measurement by P. Cameron (BNL) Base-Band Tune (BBQ) Measurement System

25. BBQ near transition Million turn BPM near transition Extra slides: RHIC BBQ – Mains ripple in the beam spectrum 180 Hz 360 Hz 720 Hz The BBQ sensitivity was estimated to be better than 10nm f[Hz] RHIC BBQ compared to a million turn BPM Measurement by P. Cameron (BNL) Base-Band Tune (BBQ) Measurement System

26. Extra sides: SPS BBQ – mains ripple in the beam spectrum 72 LHC bunches, 1011 p+/bunch, 270 GeV, coasting (RF on) Even around 5kHz, placing the tune on a 50Hz multiple increases beam oscillations! 50Hz No explicit excitation Base-Band Tune (BBQ) Measurement System

27. Extra slides: PS BBQ – Mains ripple in the beam spectrum 10 lines spaced by100 Hz 2 injections, 6 bunches, 81012 p+/bunch,1.4-26 GeV, splitting into 72 bunches Base-Band Tune (BBQ) Measurement System

28. Extra slides: LEIR – Beam not (too much) bunched H plane V plane 200 ms after injection, no kicks, average on 100 cycles Base-Band Tune (BBQ) Measurement System