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PEP-II Status

This presentation by U. Wienands outlines the progress of Run 4 at PEP-II, including increased delivery rates, machine tuning efforts, encountered issues, and improvements for the upcoming runs. Learn about the significant achievements and strategic studies vital for upgrades.

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PEP-II Status

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  1. PEP-II Status U. Wienands, PEP-II Run Coordinator …for the PEP-II team

  2. Outline of Talk • Run 4 Synopsis • Machine tuning & improvements • Issues encountered during Run 4 • Other improvements and MD items • Outlook: the remainder of Run 4… U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  3. Run 4 Synopsis • PEP is now delivering twice the rate of Run 3 • Over 60/fb delivered in Run 4, over 200/fb tot • Key ingredients: • trickle-charge both rings • Raise peak Lumi to 8.34E33 (currents, ß*, orbit) • Aggressively track down & reduce rf trips. • MD program focused on near-term improvements+ strategic studies needed for upgrades. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  4. Run 4 Delivered Luminosity U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  5. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  6. Running 7-day Integral (2004) U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  7. Run Time Accounting, Run 4 BaBar up from ≈56% to 60% Tuning/Fill down from ≈22% to 20% Downtime down from 16…19% to 14% U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  8. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  9. Machine Tuning and Improvements • LER & HER trickle charge • Steering of the HER • Lowering ßy* of the HER (12–>11 mm) • Raising of the HER rf voltage • Raising the number of bunches & beam currents U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  10. LER Trickle Charge • PEP issues mostly resolved last fall • BIC, diagnostics software • Extended BaBar trickle test late Oct. 03 • followed by analysis of data quality • Trickle in production beginning Dec. 2,03 • Daily luminosity up from 250 to 350/pb • ≈15% is direct trickle gain, • remainder is increased efficiency (less trips) • Dec. a particularly stable month for rf. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  11. LER only Trickle Day U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  12. LER Trickle Background Monitor FFT of Injection- triggers (s harmonics if off energy) Injection-generated triggers(∫ also avail. as EPICS PV) U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  13. HER Trickle Charge • 1st test in Feb. 04 • significant reduction in injection background • not at full beam current, high radiation spikes • 2nd test mid-March 04 • Radiation spikes no longer an issue due to cleanup work in injector • Break-even luminosity reached. • BaBar state machine now ready for double trickle • Double-trickling operationally since March 11. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  14. Double-Trickle Gain LER-only trickleav-to-pk = 87% Double trickleav-to-pk = 99% => 12% gain U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  15. Almost Best Day of PEP-II The best day actually had 669/pb delivered. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  16. HER Steering • Steer the HER “flat” except for IR 2 • this has worked historically • IR 2 steering in the past has caused difficulties with coupling • Motivation • lower vertical dispersion • better acceptance • better agreement of the lattice with the design U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  17. Orbit (absolute) Y dispersion Coupling (C12,n) ßx/ßx,design U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  18. Before ßy* reduction ßy* ≈ 12.3 mm ßx* ≈ 28 cm Benefit for luminosity HER beam “stronger” 3% increase in spec. lumi. Before STDZ After ßy* reduction ßy* ≈ 11.0 mm ßx* ≈ 27 cm After STDZ ßy* ≈ 10 mm ßx* ≈ 25 cm ßx* lower due to larger global ßx beat. HER ßy* Reduction We used 60% of a knob designed to bring ß* down to 10 mm Significant tuning work required post-STDZ to regain luminosity benefit U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  19. Coupling after ßy* Reduction U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  20. Lowering HER ßy* (cont’d) To be able to meaningfully reduce ßy*, we are raising the HER rf voltage. At 18 MV we expect 11 mm bunch length. The rate of rise is limited by increased rf trip rate. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  21. Fill Patterns & Beam Currents • At the beam-beam limit need to raise # bunches and beam current to gain lumi. • Need to run by-2 (4.2 ns) bunch spacing: • How will electron-cloud effects behave? • Will luminosity scale with # bunches? • What is the effect of parasitic crossings? • How will HOM heating behave? • (only the last expected to be better) U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  22. Raising # Bunches & Beam Currents Bunch currents: ≈ 1.5 mA (LER) ≈ 0.9 mA (HER) fairly constant U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  23. Spec. Luminosity vs # Bunches Fixed bunch current in both rings Fixed by-2 pattern with mini trains Vary train length, thus # of bunches U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  24. PEP Fill Patterns 1415 bunches trains of 15, 4.2 ns 1550 bunches trains of 33, 4.2 ns Note: 1st and last bunch have lower luminosity: only one parasitic xing “Pilot bunches” (no parasitics) have even less luminosity! U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  25. Luminosity vsIHER*ILER U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  26. Issues encountered • IR 2 vacuum and background issues • Rf issues • LER orbit & beam optics issues • Bunch-by-bunch feedback issues U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  27. The IR 2 Vacuum Problem • Late March, we regn’d the IR 2 NEGs • Pressure and background had been on rise • At Run 4 startup, NEGs regen’d before 1st beam • After this, LER backgrounds and pressures much worse than before • Also, long time constants (≈hours) observed • Strongly bunch-length dependent • Scrubbing very slow, almost 2 weeks • NEGs being heated by HOMs to several 100°F U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  28. LER Vac. Gauge close to IR U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  29. LER Vacuum Pump @ -28 m U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  30. NEG Temperature at -28 m In essence, the NEG is being constantly regen’d with beam! U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  31. Rf Issues • Rf has been holding up better than in Run 3 • thanks to significant effort of the RFTF • The primary issues/causes of trips • endemic failure (again) of SCRs in the HVPS • phase drifts (esp. LER 4-5) & other board issues • various tuner issues • klystron issues • misc. IOC issues U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  32. HER rf trips: 5.0/day LER rf trips: 2.0/day Total: 7.0/day HER rf trips: 2.1/day LER rf trips: 0.9/day Total: 2.3/dayincl. l. inst. 3.7/day PEP Rf Beam Aborts Run 3 Run 4 Despite the overall improvement, # rf trips actually increased significantly after Dec. 03 U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  33. LER Orbit Issues • Steer the ring without the IR, as has worked before. • LER IR steering perilous due to BPM offsets • This caused a large drop in spec. luminosity • Root cause was a large beat in ßx, also, dispersion still >50 mm rms. • No obvious quick fix => backed out • Presently using MIA to try finding a correction strategy. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  34. LER Steered Orbit U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  35. LER ßx after Steering U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  36. Other improvements and MD • BPM improvements • Modeling improvements (incl. ORM, C12) • Transverse grow-damp measurements • Longitudinal grow-damp measurements • New RF 8-1 klystron • New rf IOCs using PowerPC controllers • Injection • Crossing-angle experiment U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  37. BPM Improvements • BBA on all possible IR 2 BPM/quad pairs • Offsets from this BBA now in DB • Auto-calibration every 8 hours after a beam-dump • Timing database updated • New procedure to measure timing during delivery • See talks by Smith & Ross U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  38. Online Model Improvements • Updated online models for both rings • Survey data for IR 2 elements • More accurate parametrization of QD1 • Can run a model against machine config. & orbit • Model runs on pepoptics => can use MAD & new version of DIMAD. • C12 coupling analysis now online U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  39. HER Model vs Measurement(y) U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  40. History of ß Functions at the IP U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  41. Orbit-Response Measurements • ORM (LOCO) running on pepoptics • HER and LER data taken • ß function analysis consistent with phase-advance analysis • More work needed to understand quad-strength factors • => presentation by C. Steier U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  42. HER ORM ß/ßdesign U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  43. HER ORM – Magnet strengths Relative to design strengths. E(HER) = 8.9732 GeV U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  44. Multibunch Stability • Grow-damp measurements • HER: longitudinal & transverse • HER transverse: • good margin in x, strong nonlinearity in y, • longitudinal: only 20…30% margin for low-lying long. modes • Low-group-delay Woofer significantly better. • As a result of the HER measurements, we raised priority on the new Woofer U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  45. HER TFB Damping (x) HER X damping Data suggest stability up to 2…3 A beam current by-2 fill pattern. U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  46. Crossing Angle Experiment • Xing angle or not for the IR upgrade in 2005? • Measurements done: • Sensitivity of ∑x to beam-beam • Sensitivity of Lumi to xing angle vs currents • Results: • L vs x separation becomes narrow at high I • L vs x’ becomes somewhat narrower at high I U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  47. Xing Angle Expt: Lum. vs ∂X Simulation by I. Narsky using 3-d code by Y. Cai U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  48. Injection Orbit Feedbacks • With both rings trickling injection problems are highly visible. We are implementing feedback systems to stabilize the beams • LER injecting beam now working, HER to follow • requires BPM hardware changes • Ring-orbit stabilization under development • tricky because of modeling issues • (Note: we do not let the GOFs steer at injection) U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  49. LER Injection Orbit Feedback U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

  50. Rf Improvements • New PowerPC IOC processors • Old 68k units above 80% CPU load, causing stalls • New LLRF boards • New SLAC klystron for HER 8-1 U. Wienands, SLAC-PEP-II PEP MAC, 15…17-Apr-04

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