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Schottky Measurements in RHIC Peter Cameron

Schottky Measurements in RHIC Peter Cameron. Outline. RHIC systems overview System-by-system 2GHz resonant cavity pickups 245MHz resonant stripline pickups ‘Transition Chromaticity Monitor’ 1.7GHz traveling wave pickup BBQ?. RHIC Systems Overview. Schottky systems history at RHIC:

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Schottky Measurements in RHIC Peter Cameron

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  1. Schottky Measurements in RHIC Peter Cameron Care Workshop Dec 2007

  2. Outline • RHIC systems overview • System-by-system • 2GHz resonant cavity pickups • 245MHz resonant stripline pickups • ‘Transition Chromaticity Monitor’ • 1.7GHz traveling wave pickup • BBQ? Care Workshop Dec 2007

  3. RHIC Systems Overview • Schottky systems history at RHIC: • early years – owned by BI group, vigorous development work, productive data delivery, Nat Inst DAQ, labview interface to Controls • middle years – owned by BI, attempt to upgrade DAQ and Controls interface stymied by Pentek DSP issues, personnel changes • recent years – owned by AP, very little progress (going backwards?), very little data delivery, DAQ limitations, focus on custom C-code,… Care Workshop Dec 2007

  4. High Frequency Schottky • Built by LBNL - follow on to FNAL system (W Barry et al, EPAC 98) • Gold in RHIC gives ~+18dB relative to protons • Three cavity modes • TM210 - Horizontal 2.067GHz • TM120 - Vertical 2.071GHz • TM111 - Longitudinal - 2.721GHz (used by RF guys for cavity phasing) • Cavity properties • Qloaded ~ 5000, Transverse impedance ~ 9 MW/m • DAQ • LO at 2.069GHz mixes both transverse modes to 2MHz • filter, mix to base band, acquire with SRI DSA Care Workshop Dec 2007

  5. HF Schottky Cavity Care Workshop Dec 2007

  6. RHIC 2000 – HF Schottky the first transition crossing 100msec transition ramp tunes Care Workshop Dec 2007

  7. Polarized Protons – RHIC 2001 Care Workshop Dec 2007

  8. HF Schottky at Store - RHIC 2001 Flat top 200MHz on tunes Care Workshop Dec 2007

  9. HF Schottky at Store RHIC 2001 chromaticity DAQ was Nat Inst 5MS/s A/D in MacIntosh, running LabVIEW, interfaced to controls via SNAP Care Workshop Dec 2007

  10. Spectral effects of beam out of bucket,beam offset plus dispersion (transverse mode) asymmetric rev line (due to beam offset plus dispersion?) beam out of bucket 197 MHz off no asymmetry in longit mode 197 MHz on Care Workshop Dec 2007

  11. HF Schottky Cavity Care Workshop Dec 2007

  12. motion control to overcome rev line saturation Care Workshop Dec 2007

  13. e calibration - the principle • Simple • Schottky pickup is moveable controllable beam offset • Schottky signal is macro-particle of charge sqrt(N), where N is number of beam particles • This macro-particle deposits power in the spectrum at both revolution and betatron frequencies • Beam/pickup offset at which power in rev line equals power in betatron line is the rms beam sigma (see next slide) • For preliminary exploration we just did this by eye • For proper calibration need to take fill pattern into consideration, use WCM to calibrate to correct rev line Care Workshop Dec 2007

  14. Spectra at 3 pickup positions Counts = 75 Counts = 675 Counts = 1275 Care Workshop Dec 2007

  15. mirrored down for least squares fit Departure from straight line indicates non-Gaussian profile, can be fitto determine profile Care Workshop Dec 2007

  16. Comparison with IPM – RHIC 2005 flattop • Resolution > x10 better • No beam kick • May be useful on ramp • Schottky point every 4 sec Care Workshop Dec 2007

  17. Yet more comparison with IPM Schottky IPM These differences are meaningful? – related to shape of transverse profile? Care Workshop Dec 2007

  18. Sideband widths – 3 terms 1 2 3 3dB to rms where Care Workshop Dec 2007

  19. this line is a sideband of a rev line that is 28 lines that way for tune below the half integer this line is a sideband of a rev line that is 28 lines that way rev lines betatron lines Care Workshop Dec 2007

  20. Chattopadhyay CERN SPS 84-11 Care Workshop Dec 2007 http://documents.cern.ch/cgi-bin/setlink?base=cernrep&categ=Yellow_Report&id=1984-011

  21. Schottky DSP System 28MHz LLRF Distribution LFS 2-Channel/box Receiver’s HFS Tracking LO’s 3-Quad C6701 Floating Point Pentek DSP boards LabView Applications Running on Linux HFS 2-Channel/box Receiver’s (4-Transverse) (2-Longitudinal) Care Workshop Dec 2007

  22. Present LF and HF Schottky DAQ Care Workshop Dec 2007

  23. Outline • RHIC systems overview • System-by-system • 2GHz resonant cavity pickups not in use so far in Run 8 , minimal use in Runs 6 and 7 • 245MHz resonant stripline pickups • ‘Transition Chromaticity Monitor’ • 1.7GHz traveling wave pickup • BBQ? Care Workshop Dec 2007

  24. Resonant BPM • M. Kesselman et al - PAC 2001 • Stub-tuned 1/4 wave resonator • Simulated in Spice • frequency ~ 240MHz (8.5xRF) • Qloaded ~ 100 optimal coupling • In-tunnel hybrid for S and D • Resonate difference mode - not sum mode signal at revolution line • Moveable - minimize difference mode signal at revolution line • Resonate above coherent spectrum Care Workshop Dec 2007

  25. Moveable Resonant BPM Care Workshop Dec 2007

  26. lineshape- space charge? LF Schottky at Injection Span 78KHz 5dB/div dq = hNdp/p ~ 2 KHz h ~ .007 N ~ 3060 dp/p ~ .001 Care Workshop Dec 2007

  27. LF Schottky on the Ramp – RHIC 2001 Injection Transition Care Workshop Dec 2007

  28. Status of LF Schottky Care Workshop Dec 2007

  29. Outline • RHIC systems overview • System-by-system • 2GHz resonant cavity pickups not in use so far in Run 8, minimal use in Runs 6 and 7 • 245MHz resonant stripline pickups tune at store only • ‘Transition Chromaticity Monitor’ • 1.7GHz traveling wave pickup • BBQ? Care Workshop Dec 2007

  30. Transition Chromaticity Monitor • RHIC luminosity with Ions limited by transition • Need to measure chromaticity around transition – model is not adequate • Time resolution needed ~100msec • only feasible diagnostic for tuning chrom at transition is Schottky? • Narrow linewidths give good S/N • Ions give good S/N • If need be provide additional white noise excitation Care Workshop Dec 2007

  31. “Continuous Beam Transfer Function” RHIC ramp with white noise excitation, octupole tune spreadandasymmetry in chromaticity around transition clearly visible horizontal transition Ramp 8311 blue ring as seen by BBQ vertical Care Workshop Dec 2007

  32. beam 245MHz from LF Schottky kicker 10W RF power amp LFS DAQ splitter ‘line hopping’ not needed 245MHz 245MHz 243MHz 243MHz x32 1.9MHz 1.9MHz Xtal filter 70KHz BW NCO NCO 1.9MHz filter 70KHz BW filter 192KS/s A/D 1002a white noise MCR LabVIEW Care Workshop Dec 2007

  33. ramp data from ‘Transition Chromaticity Monitor’ saturation around transition Care Workshop Dec 2007

  34. Care Workshop Dec 2007

  35. Care Workshop Dec 2007

  36. Care Workshop Dec 2007

  37. Care Workshop Dec 2007

  38. Care Workshop Dec 2007

  39. Care Workshop Dec 2007

  40. Outline • RHIC systems overview • System-by-system • 2GHz resonant cavity pickups not in use so far in Run 8, minimal use in Runs 6 and 7 • 245MHz resonant stripline pickups tune at store only • ‘Transition Chromaticity Monitor’ all is well, excepting saturation at transition (secondary issue – LO phase noise?) • 1.7GHz traveling wave pickup development continues, eventual abort gap monitor • BBQ? Care Workshop Dec 2007

  41. FFT of BBQ AFE excitation here is only mains harmonics, perturbed by AGS Booster cycle every 4 sec Care Workshop Dec 2007

  42. Summary/Conclusion • A lot of good hardware available • A serious need to get all possible data from the available systems • Seriously underutilized for several years, due to a variety of circumstances. Care Workshop Dec 2007

  43. Backup Slides Care Workshop Dec 2007

  44. Sideband widths – 3 terms 1 2 3 3dB to rms where Care Workshop Dec 2007

  45. Envelopes of the modified Bessel functions for chromaticity = 0 The amplitude of a given order Bessel function determines the amplitude of the same order synchrotron satellite at that frequency Care Workshop Dec 2007

  46. Envelopes of the modified Bessel functions for chromaticity = 2 Center of the envelopes is shifted by the chromatic frequency (~80MHz for RHIC parameters) Care Workshop Dec 2007

  47. Care Workshop Dec 2007

  48. a1 is not a concern? Care Workshop Dec 2007

  49. kicker LF Schottky 245MHz beam baseband out 10W RF power amp rear panel 300MHz low-pass 250MHz hi-pass cavity bandpass rear panel 300MHz low-pass 250MHz hi-pass -10dB coupler x2 x2 kicker box receiver box x16 x16 -3dB 19dB 19dB 1.9MHz bandpass 70KHz BW 1.9MHz low-pass 1.9MHz bandpass 70KHz BW -10dB -10dB 19dB splitter front panel front panel splitter RF sample baseband out white noise Care Workshop Dec 2007 NCO NCO

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