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PEP-II RF System Status and Upgrades

PEP-II RF System Status and Upgrades. By: Vojtech Pacak Klystron Department PEP-II Machine Advisory Committee Review January 18-20 2006. Summary. RF system performance Configuration inventory Status of selected problems reported in Dec 2004 MAC meeting RF aborts, run 5A/B

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PEP-II RF System Status and Upgrades

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  1. PEP-II RF System StatusandUpgrades By: Vojtech Pacak Klystron Department PEP-II Machine Advisory Committee Review January 18-20 2006

  2. Summary • RF system performance • Configuration inventory • Status of selected problems reported in Dec 2004 MAC meeting • RF aborts, run 5A/B • List of leading abort causes • Klystron status • Limitations and Spare klystrons • RF system upgrades • New HER stations 10 and 11 • Conclusions

  3. 1) RF System Configuration – Runs 4-5-6* * Luminosity predictions assuming y, y* and n remain fixed.

  4. 2) Status of Selected Problems Reported in Dec 2004 • Stuck/Slow Tuners • Found a software bug causing the motor controllers to hung up. New software installed in SPEAR3. Software will be installed in PEPII. • SCR Stacks • Problem of leaking hermetic oil seals of SCR’s fixed. • All phasing SCR’s work fine. • Crowbar SCR’s develop excessive leakage in certain manufacturing lots. Investigated by SLAC and EUPEC . • HER 12-6 Cavity Arcs • Was traced to arcing in the cavity monitor probe • A new probe installed in the auxiliary cavity probe location fixed the problem. • HER 8-3 Cavity D Arcs • Still not understood why the cavity probe signal would increase with the increase of cavity reflected power. • Occurrence increases with HER beam current. • Could be caused by arcing in the coupler box?

  5. Courtesy: Dan Van Winkle 3) Run 5A Abort Statistics, 4/21/05-10/17/05 Average of 4.5 Aborts/Day (2.8 Aborts/Day without non-RF events) Compared to 2.9/Day for Run 4

  6. Courtesy: Dan Van Winkle 3) Run 5B Abort Statistics, 10/11/05-1/17/06 Average of 5.5 Aborts/Day (0.8 Aborts/Day without non-RF events) Compared to 2.9/Day for Run 4

  7. 3) Leading RF caused aborts – run 5A/B • Cav1(2) arcs, Cav1(2) vacuum, 75,36 counts • Majority (~80%) in HER 8-1 and HER 12-1.These trips have been observed for many years. Cav1 is the first the beam enters after the beam pipe arcs. The deposit of out gassing debris from the arcs into these cavities are believed to be the probable cause. • Typically the operating voltage of these cavities is reduced to limit arcing • Klystron Arc, 41 counts • About 50% of reported aborts happened during testing, (Philips #7,LER 4-3), or during the HV processing of the klystron, (Philips #8,HER 12-6). • Observed arcing in Philips #7, (LER4-3). • klystron voltage set < 73 kV • HVPS dips or rise, 30 counts • Few milliseconds voltage reduction or rise leads to klystron oscillations. Affected HER 4-1 and LER 4-2 • HVPS re-phased • Drive glitch, LER 4-4, 26 counts • Station LLRF power supply has been changed. Problem may be fixed, but need more confirmation. • Klystron output RE, HER 12-6, 12 count • Corrected by adjusting circulator coil current. • Power dips, 11 counts • HV reduction in all RF stations in the region. Mostly region 8, also observed in region 4. • Ongoing investigation

  8. 4) Klystron Issues Output power limitation on 4 klystrons: • HER 4-1 (Philips #2) • Klystron saturation in Philips #2, power limited at ~ 850 kW • Adjusted klystron focus magnetic field, output match, circulator bias and waveguide length – no improvement! • HER 12-1 (Philips #6) • Klystron saturation in Philips #6, power limited at ~ 750 kW • Evidence of multipacting • HER 12-2 (SLAC #6) • Sideband oscillations 15 MHz, power limited at ~850 kW • Tuning of the circulator may mitigate the problem • LER 4-5 (Philips #3) • Klystron saturation in Philips #3, power limited at ~850 kW, sideband oscillation 3 MHz Hours of Operation: • HER 12-5, HER 4-1, HER 12-3, LER 4-5 • Klystrons Philips #’s 1, 2, 3 and SLAC #1 near or exceeding 50,000 filament hours Spare Klystron Status • Currently Philips #5 is the only spare until SLAC #8 is tested • It has deformed collector body and is power limited to ~ 600 kW • Only after installation of the new SLAC klystrons there will be more Philips tubes as spares

  9. 4) Klystron Manufacturing Schedule Courtesy: Chris Pearson, KLY

  10. Shutdowns 4) Klystron Replacement Schedule Power Limited Installation SLAC Tubes Run 5B Run 6 Run 5A NOW

  11. 5) PEP-II RF Station Installation Install 2006 shutdown

  12. 5) RF Stations Upgrades • Two New RF stations • HER10, new station 12-4, split 12-3.shutdown 2006 • HER11, new station 4-6.shutdown 2006 • Manufacturing/Delivery - major parts • Resonators. • Manufacturing under process at ACCEL • Expected delivery end of May 2006 • Assembly and testing at SLAC May – July 2006 • Klystrons. • SLAC #10 and Philips #4 • Expected delivery May – August 2006 • Circulators. • On site • Waveguides, Loads. • Partially Ordered • Expected delivery end of May 2006 • HVPS and SCR’s stacks. • Ordered • Expected delivery March 2006

  13. 6) Conclusions For Run 5: • RF system works in general reliably this run! • RF abort rate averaged 3/day, compared to 2.9/day for Run 4. • Currently 3 power limited klystrons in the HER, 1 in LER. • ~55% of all RF aborts caused by: • Klystron arcs in LER 4-3 and HER 12-6. • 4-3 operates with limited voltage, replaced klystron in 12-6 • Arcing or vacuum trips of cavity #1/2 in HER 8-1 and 12-1 stations. • Lower cavity voltage when arcing may cause the problem • HVPS. • Ongoing investigation of SCR’s failures and region power dips • 3 new SLAC tubes plus 2 repaired Philips klystrons by mid of 2006. • Improved situation with spare klystrons. • Starting in March, new klystron delivery in every ~ 5 weeks. For Run 6: • Two new HER RF stations, #10-(HR12-3 split) and #11-(2-cavity HR4-6). • Up to 3 more new/repaired klystrons ready for installation in LER.

  14. Acknowledgements • To all members of the PEP-II RF Systems Taskforce from the following SLAC departments: • ARD-A  LFB Systems • ESD  LLRF and Software Systems • Klystron  High Power RF and TFB Systems • PCD  HVPS Systems • Specific thanks to Heinz Schwartz, Alan Hill, Chris Pearson, Dan Van Winkle and Marc Larrus for their input to this presentation.

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