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RHIC Optics Correction

RHIC Optics Correction. M. Bai C-A Dept., BNL Mini-workshop on ICA in Beam Measurement and Generic algorithm in Nonlinear beam dynamics, Bloomington, Indiana, March 14-16, 2012. Outline. RHIC Optics Design Offline linear model design Online implementation

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RHIC Optics Correction

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  1. RHIC Optics Correction M. Bai C-A Dept., BNL Mini-workshop on ICA in Beam Measurement and Generic algorithm in Nonlinear beam dynamics, Bloomington, Indiana, March 14-16, 2012

  2. Outline • RHIC Optics Design • Offline linear model design • Online implementation • RHIC optics measurements status • RHIC optics correction status • ORM approach • AC dipole measurement based • Summary of commissioning of SBST • Future plans

  3. RHIC Optics Design • Build linear model to fulfill desired optics functions for the entire ramp with the constraints/inputs of • Magnet transfer functions • RHIC power supply/shunt currents limit • RHIC magnets’ wire-up scheme • Smooth changes of currents as function of beam energy • This is done by MAD

  4. Flowchart of RHIC optics design Courtesy of S. Tepikian, BNL

  5. RHIC Optics Design • Build linear model to fulfill desired optics functions for the entire ramp • Output: magnet strength as function of beta* • Handover the designed magnet strength as function of beta* to OptiCalc, RHIC online model • OptiCalc then re-generates beta functions for the entire ramp for machine operation. • Mode details on RHIC online model are discussed by G. Robert-Demolaize tomorrow

  6. RHIC Optics Measurement Techniques

  7. Status of RHIC Optics Measurement • Routine full ring beta/phase beat measurement using ac dipole for each operational lattice • Routine ac dipole setup: 0.01 away from betatron tune. A known systematic of ~6% • Each optics measurement is the average of at least 3 data sets in each plane. Each data set has 1024 turns. The bpm noise is less than 5%

  8. Measured Beta and Phase advance: Blue@100 GeV

  9. Status of RHIC Optics Measurement • Routine full ring beta/phase beat measurement using ac dipole for each operational lattice • Routine ORM measurement • Routine beta* measurement • using ac dipole • Modulating triplet quadrupoles • ORM

  10. Status of RHIC Optics Corrections • Focused on commissioning LOCO at RHIC before RUN10 • Initiated by T. Satogata ~ 6 years ago • limited quadrupoles to avoid degeneracy problem • Lumped triplet quads, Q4,Q6,Q8. Dual bpms are available at these quadrupoles • The data analysis shows the fits should be available to correct 15~20% beta-beat • Application of ORM analysis to actual machine was a mixed results • BPM data quality

  11. Status of RHIC Optics Corrections • Introduced SBST technique in RUN11 of pp • SBST: Sector By Sector Technique • It was first developed at LHC led by Dr. R. Tomas, “CERN Large Hadron Collider optics model, measurements, and corrections”, Phys. Rev. ST Accel. Beams 13, 121004 (2010) • The essence of this technique is to identify localized gradient errors. It assumes that the measured beta-beat mainly comes from the the gradient errors of triplets in IP with small beta* • Under this assumption, SBST treats part of machine as beamline with initial conditions matched to the measured twiss parameters • Then calculate the difference of measured phase advance vs. the model phase advance at each bpm • Can also be used to identify the local coupling error, dispersion error, etc.

  12. SBST Analysis of RHIC Blue Ring at 100 GeV IP 8

  13. SBST Commissioning in RUN11 • Initial IP6 correction helped to reduce the vertical beta-beat except sector 12-1 and sector 2&3 Calculated: Q5I6, 0.95 Q5O6, 0.96 Actual applied correction: design trim bi5-qf7 0.078881 0.00135248944 bo6-tq5 0.0211343 -0.0029438348

  14. Effect of IP6 Correction Fill15161

  15. Summary of SBST Commissioning • Initial IP6 correction helped to reduce the vertical beta-beat except sector 12-1 and sector 2&3 • IP8 correction wasn’t effective in vertical. And it showed mixed effects on the horizontal beta-beat Calculated: Q6OT8,0.99, Q5OT8,0.9, Q3I8,1.0005, Q5IT8,0.98

  16. Effect of IP8 Correction Fill15329

  17. Summary of SBST Commissioning • Initial IP6 correction helped to reduce the vertical beta-beat except sector 12-1 and sector 2&3 • IP8 correction wasn’t effective in vertical. And it showed mixed effects on the horizontal beta-beat • Together with IP6 correction, IP12 correction shows moderate effect on horizontal beta-beat at the expense of vertical beta-beat. This solution also affected beta* at IP6 and IP8

  18. Baseline, IP6, IP12+IP6

  19. Summary of SBST Commissioning • Initial IP6 correction helped to reduce the vertical beta-beat except sector 12-1 and sector 2&3 • IP8 correction wasn’t effective in vertical. And it showed mixed effects on the horizontal beta-beat • Together with IP6 correction, IP12 correction shows moderate effect on horizontal beta-beat at the expense of vertical beta-beat. This solution also affected beta* at IP6 and IP8 • Together with reduced IP6 correction, IP4 correction shows moderate effect on vertical beta-beat except sector 6&7. No significant effect on horizontal beta-beat

  20. SBST Analysis IP12, Fill 15161

  21. Encountered Issues • Limited knobs • RHIC nesting power supply scheme

  22. Encountered Issues • Limited knobs • RHIC nesting power supply scheme

  23. Encountered Issues • Limited knobs • RHIC nesting power supply scheme • limited independent knobs: trim quads at Q5, Q6 • Power supply limit • Reproducibility of optics

  24. Reproducibility?

  25. Encountered Issues • Issues • Limited knobs • Reproducibility of optics • Complicated RHIC modeling infrastructure • Two model engines for RHIC: mad and online model(Opticalc) • They don’t carry exact the same lattice, for instance, the crossing angles, local coupling corrections, etc. • Each model uses slightly different magnet transfer function • For mad, it assumes the same transfer function for the same type of magnets • For online model, the actual measured transfer function for each magnet is used

  26. Beam not centered in Quads Applying 40% IP2+12 correction removing 40% IP2+12 correction 80% IP6, 20% IP12 correction and IP2 20% 80% IP6, 20% IP12 correction 80% IP6 correction Applying 80% IP6 correction Removing all correction

  27. Summary • First experience of SBST at RHIC was encouraging • Latest SBST analysis of latest RHIC 100 GeV pp operation indicates there is no gross local gradient errors in Blue IR. The measured beta-beat is ~10% rms. This is consistent with 0.85m beta* at 100 GeV • SBST is also very sensitive to bpm timing, …. • In order to reach less than 10% beta-beat, one needs to consider global optics correction as demonstrated in LHC

  28. Global Optics Correction • What is it? Phase advance • Calculate gradient deviation from the model • Only work for small perturbation and assume the model is pretty close to reality • Demonstrated proof-of-principle in RUN2009 ago with a dialed-in gradient error of one of the IR trim quads • Briefly tested correction at injection with only IR trim quads. No conclusions due to limited data

  29. Measured Beta-Beat: Blue • rms beta-beat in arcs is under 10% • large beta-beat spikes at IP8 not quite • understood. Investigating …

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