1. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 1 Base-Band Tune (BBQ) Measurement System Marek Gasior Beam Instrumentation Group, CERN

2. M.Gasior, CERN-AB-BIBase-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)

3. M.Gasior, CERN-AB-BIBase-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

4. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 4 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 3 dB

5. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 5 Tune measurement – Direct Diode Detection (3D)  Peak detection of position pick-up electrode signals (“collecting just the cream”)  f rev content converted to the DC and removed by series capacitors  f b modulation moved to a low frequency range (as after the diodes f b 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 f rev 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)

6. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 6 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 C f = C pu (PU electrode capacitance) Electrode 1 signal Electrode 2 signal Signals of both peak detectors Detector signal difference sd(t)sd(t)

7. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 7 Direct Diode Detection – The principle  = 0,  = 0.01 q = 0.1, C f = C pu  = T  = 100 T 4 bunches  = 100 T Detector signal differenceSignals of both peak detectors

8. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 8 Direct Diode Detection – Diodes not perfect Detector signal differenceSignals of both peak detectors  = 0,  = 0.01 q = 0.1, C f = C pu 4 bunches  = 100 T beam not centered one bunch 10 % larger

9. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 9 q  0.5 Direct Diode Detection – Base band spectrum q  0.5

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

11. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 11 BBQ systems at CERN LHC, SPSPS, PSB, LEIR  BBQ system operational at RHIC  Tested at Tevatron  Will be operational at the CNAO hadrontherapy machine

12. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 12 SPS BBQ

13. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 13 SPS BBQ – Transverse damper noise 1 bunch LHC pilot,  5  10 9 p +, 26-450 GeV Damper system OFF No explicit beam excitation Damper system ON

14. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 14 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 (no filters)

15. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 15 PS EASTB, regular kick every 10 msTOF, regular kick every 10 ms

16. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 16 PSB LHC25A, R3, no kickSame, kick 20 V (a % of the standard kick)

17. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 17 LEIR NOMINAL, regular kick 500 V, every 10 msSame, no kick

18. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 18 (Sound card) Record of the RHIC BBQ signals Horizontal plane (L) Vertical plane (R) about 10 minutes injectionsrampsqueeze RF switching Q' too small

19. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 19 Spectra of the RHIC BBQ signals Hor.Ver.

20. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 20 RHIC BBQ measurements – Collisions Store beginning H plane V plane 5 hours later (end of the store) H plane V plane

21. M.Gasior, CERN-AB-BIBase-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)

22. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 22 Extra slides: Direct Diode Detection – SNR limits  = 100 T

23. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 23 Extra slides: PS BBQ – Detector DC voltages AD SFTPRO TOF

24. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 24 Extra slides: RHIC BBQ – Tune scan Measurement by P. Cameron (BNL)

25. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 25 Extra slides: RHIC BBQ – Mains ripple in the beam spectrum Million turn BPM near transition BBQ near transition 180 Hz720 Hz360 Hz f [Hz] Measurement by P. Cameron (BNL) RHIC BBQ compared to a million turn BPM The BBQ sensitivity was estimated to be better than 10 nm

26. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 26 Extra sides: SPS BBQ – mains ripple in the beam spectrum 72 LHC bunches,  10 11 p + / bunch, 270 GeV, coasting (RF on) Even around 5kHz, placing the tune on a 50 Hz multiple increases beam oscillations! 50Hz No explicit excitation

27. M.Gasior, CERN-AB-BIBase-Band Tune (BBQ) Measurement System 27 Extra slides: PS BBQ – Mains ripple in the beam spectrum 10 lines spaced by 100 Hz 2 injections, 6 bunches,  8  10 12 p + / bunch, 1.4-26 GeV, splitting into 72 bunches

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