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Beam-beam and BTF

Beam-beam and BTF. W. Fischer, P. Cameron. RHIC Accelerator Physics Experiments Workshop, BNL, 3 November 2006. can extract r ( w ) with W -scan. In-phase response. Out-of-phase response. [A. Chao, “Physics of collective beam instabilities …”, Chapter 5].

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Beam-beam and BTF

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  1. Beam-beam and BTF W. Fischer, P. Cameron RHIC Accelerator Physics Experiments Workshop,BNL, 3 November 2006

  2. can extract r(w)with W-scan In-phase response Out-of-phase response [A. Chao, “Physics of collective beam instabilities …”, Chapter 5] Transfer functions give tune distributions • Have collection of oscillators (particles) with frequency distribution r(w) • Have external driving force Ae-iWt • Coherent response of particle distribution after transient effects is

  3. BTF application • Hardware from Q & DQmin-feedback (P. Cameron) • Application initiates scan, collects data, archives (J. Laster) Last year application showed amplitude (and phase) of response.This is not the tune distribution.

  4. excitation frequency measured amplitude measured phase normalization factor unknown phase offset Tune distribution from BTF application

  5. Amplitude and phase of BTF measurement Store 7949

  6. Determination of phase offset • Phase offset y0 does not change from store to store • For symmetric tune distributions r(w) (no beam-beam), phase cos(yBTF–y0) goes through zero when amplitude ABTF is at maximum  Fit y0 with non-colliding beam, average over a sufficiently large number of measurement, use fixed number in BTF application

  7. DQ  0.009 Tune distribution, beam-beam OFF and ON [Store 7949, no phase offset correction.] Tune spread expectation from intensity and emittance DQbb,tot = 0.010

  8. BB OFF BB ON DQ = 0.008 Calculated tune distributions • beam-beam • no amplitude dependent tune shift from nonlinear IR magnet errors (not sure tracking model is correct) • nonlinear chromaticity and momentum spread(up to 3rd order in dp/p – Harmon, S. Tepikian) • Random points in (x,y,dp) from Gaussian distributions, tune calculation and sorting into histogram (Mathematica) Not all features of measurement reproduced.

  9. BTF Improvements • Eliminate frequency steps (pointed out by Mike Bl.) • Optimize sweep rate (fast, but no transient effects) • Determine phase offset y0 with small error • Systematically analyze tune distributions,should be able to explain all features • Analyze BTFs across beams (excite one beam, measure other – done already by Pete)

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