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Beam-beam wire compensation, status and plans

Beam-beam wire compensation, status and plans. W. Fischer R. Calaga, Y. Luo, BNL ; V. Ranjbar, T. Sen, FNAL ; U. Dorda, J.-P. Koutchouk, F. Zimmermann, CERN ; J. Qiang, LBNL ; A. Kabel, SLAC ; J. Shi, KU. RHIC Accelerator Physics Experiments Workshop, BNL, 2 November 2006. Content.

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Beam-beam wire compensation, status and plans

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  1. Beam-beam wire compensation,status and plans W. Fischer R. Calaga, Y. Luo, BNL; V. Ranjbar, T. Sen, FNAL; U. Dorda, J.-P. Koutchouk, F. Zimmermann, CERN; J. Qiang, LBNL; A. Kabel, SLAC; J. Shi, KU RHIC Accelerator Physics Experiments Workshop,BNL, 2 November 2006

  2. Content • Long-range beam-beam effect in RHIC • Status • Beam tests so far (2005/2006) • RHIC BBLR wires • Simulations • Plans

  3. 52.4 ns 15.7 m 45.0 ns 13.5 m 32.7 ns 9.8 m DX IP DX BPM(x,y) BPM(x,y) Long-rangeinteractions with 360 bunches      NO long-range interactions with 120 bunches      Long-range interactions with 180 bunches RHIC interaction region • Currently (120 bunches) no long-range interactions in store • Can create 1 or 2 long-range interactions per IR • With >120 bunches cannot avoid long-range beam-beam interactions (possible upgrades like eRHIC)

  4. long-rangeinteraction(vertical) long-rangecompensation(up) RHIC Sector 5 bi5 Dfx,y = 6 deg (b* = 1m) yo5 long-rangecompensation(down) RHIC – possible location for compensation IP6 Small phase advance between long-range beam-beam interactionand possible compensator can only be realized at store.

  5. d Long-range beam tests in RHIC Basic experiment: • Have large vertical separation in all IRs • Adjust rf to have LR interactions at desired location • Change vertical separation by moving one beam • Observe beam lifetime of other beam Comments: • Beam lifetime most sensitive observable (almost no other) • Need DCCT and multiple bunches for good measurement[single bunch intensity measurement from WCM too noisy]

  6. attempts to improve lifetime, small changes in (Qx,Qy) Single LR effect at injection (24 GeV p) Collision at s = 10.6 m,Blue beam moved vertically Tunes B (0.739,0.727) Y (0.727,0.738) Effect well observable at injection. (Compensation not possible at injection due to large phase advance across triplet.)

  7. Single LR effect at store (100 GeV p) Collision at s = 10.6 m,Yellow beam moved vertically (after 15:00) Tunes B (0.739,0.727) Y (0.727,0.738) Conditions found after tune scan. Additional octupoles on in Yellow.

  8. 3.5s separation 6s separation ~0.002 Single LR effect at store (100 GeV p) Blue vertical tune distribution from BTF measurement.(Yellow beam was moved – Blue is the probe.) [Hardware for BTF measurement part of the Q&DQmin-feedback system – P. Cameron et al.]

  9. 6s separation 3.5s separation 0.002 Single LR effect at store (100 GeV p) • Calculated Blue tune distributions including: • long-range beam-beam • amplitude dependent tune shift from nonlinear IR magnet errors (up to 2nd order in action from –incorrect– tracking model, Y. Luo) • 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) Width of tune distribution reproduced, but not details[BTF tune step size, BTF noise, BTF phase offset, model not accurate enough, …]

  10. 3.5s separation 6s separation Single LR effect at store (100 GeV p) Yellow vertical tune distribution from BTF measurement.(Yellow beam was moved, additional arc octupoles on.)

  11. (0.73,0.74) (0.7,0.7) (0.68,0.68) e-growth simulations J. Qiang, LBNL Conditions: 100 GeV protons Nb = 21011 en,rms = 15 mm mrad (dp/p)rms = 0.003 (xx,xy) = (2,2) • 4s separation • 50k turns • 82k particles • Nonlinearities • beam-beam • arc sextupoles • e-growth in %

  12. Tune footprint simulation – U. Dorda (CERN) • RHIC • linear lattice incl. arc sextupoles, beam-beam force, rf off • no triplet errors yet • 0-6 s particle amplitudes, 0.5-10 s beam-beam separation

  13. Beam-beam Simulations for RHIC • FNAL – V. Ranjbar, T. Sen Code BBSIM • LBL – J. Qiang Code Beambeam3D • SLAC – A. Kabel Code PlibB Web site for results http://www-ap.fnal.gov/~tsen/RHIC/

  14. Loss Rate vs Beam separation

  15. Analysis of RHIC Experiment on May 3rd Beam separation decreased from 4 to 2 sigma by moving the yellow beam. • Tunes: • BBSIM simulations for blue beam show that Qx, Qy move down by about 0.001 • Observations: Qx went down by 0.0005 and Qy went down by 0.0012. Variation in Qx was probably within measurement error since measurements made at intermediate sigma separations yielded lower tunes. The magnitude and direction of the tune change agreed with BBSIM predictions in the vertical plane. • Power in the Tune signal • BBSIM: power halves in the horizontal plane while the power doubles in the vertical plane • Observations: The peak power went up slightly in both planes. The power in the horizontal plane went in the opposite direction predicted by BBSIM. The power in the vertical plane matches the direction of BBSIM prediction but not the size (assuming the BTF units are linear).

  16. Analysis of May 3rd experiment (contd) • Emittance growth There seems to be close agreement in horizontal emittance growth for 2 separations - but this may be fortuitous. Howevermeasurements and simulations agree on the relative growths in the horizontal and vertical planes. • Relative loss rates Level of agreement is not yet satisfactory. However more detailed analysis with additional physics in simulation model (tune modulation e.g.) will follow and for experiments on other dates.

  17. RHIC BBLR wires – design criteria • Location in the ring After Q3 in experimental IR (phase advance) • Integrated strength 10 Am for single LR, designed for 125Am (1 LHC strength) • Wire temperature < 100°C for vacuum (air cooled, 3 heat sinks, also NEG coated), allow for thermal expansion • Positioning range and accuracy wire in shadow of adjacent beam pipe if not in use, approach beam to < 3s (65mm vertical range, accuracy of 0.2 mm  0.03s) • Power supply requirements Irms/I < 10-4 (simulations F. Zimmermann, e-growth calculations) • Controls and diagnostics Local PIN diodes for loss observation

  18. Air cooled heat sink up to 1 LHC BBLR strength end with expansion loop,feed-through, and strong-back RHIC BBLR wires – design

  19. wires (2.5m long) with strong-back (-profile)7 support points NEG coated chambersduring assembly RHIC BBLR wires – assembly

  20. Planned test with RHIC BBLR wires • Better signal from LR interaction(include head-on BB as another nonlinearity, larger chromaticity) • RHIC BBLR wire commissioning(may be partially parasitic to operation, may improve collimation) • Use wires to simulate LHC-like conditions(wires designed for LHC strength, beam lifetime better than in SPS tests) • Test compensation of single LR interaction (in presence of head-on collision, need protons) • Test pulsed power supply [not in 2007](confirm that beam lifetime is not negatively affected)

  21. BBLR may improve (vertical) collimation Simulation of diffusion rates in LHC Head-on + long-range Head-on only [F. Zimmermann, Beam-Beam Workshop 2001] Increased diffusion at large amplitudes should increase impact parameter on primary collimator

  22. Summary – long-range beam-beam in RHIC Status • Beam tests so far [2005/2006 with protons]: • Measurable effect of single LR at injection (24 GeV) • Smaller effect at store (100 GeV), still measurable • RHIC BBLR wires to be installed in RHIC tunnel • Simulations show quantitative agreement with experiments in limited number of parameters only Plans for next run • Commission BBLR, explore effect on background • Tests with RHIC BBLR wires: • Test close to nominal LHC BB conditions before LHC[not possible in any other machine, should be reproduced by simulation] • Test compensation of single LR BB interaction

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