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RF System Improvements for Performance and Reliability

RF System Improvements for Performance and Reliability. Dan Van Winkle Kirk Bertsche, John Fox, Themis Mastorides, Claudio Rivetta, Heinz Schwarz. Brief Outline. Current performance and future plans Brief RF System Review What keeps us up at night Longitudinal Growth Rates Aborts

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RF System Improvements for Performance and Reliability

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  1. RF System Improvements for Performance and Reliability Dan Van Winkle Kirk Bertsche, John Fox, Themis Mastorides, Claudio Rivetta, Heinz Schwarz

  2. Brief Outline Current performance and future plans Brief RF System Review What keeps us up at night Longitudinal Growth Rates Aborts General ongoing global issues Conclusions and Outlook

  3. Current and Planed Performance

  4. Current performance and future plans Run 6 Parameters (max achieved) LER HER Beam Current 3.026 (1.4X) 1.96 A (2X) RF Voltage 4.05 16.5 MV # Cavities 8 28 # Klystrons 4 11 (1.8X) Voltage/Cav 506 590 kV Klystron Pwr 755.1 845.9kW

  5. Current performance and future plans Run 7 Parameters (max planned) LER HER Beam Current 4.00 (1.9X) 2.2 A (2.2X) RF Voltage 5 17.5 MV # Cavities 8 28 # Klystrons 4 11 (1.8X) Voltage/Cav 625 625 kV Klystron Pwr 1005980 kW

  6. Brief Overview of PEP-II RF System

  7. The PEP-II LLRF STATION REF (EPICS) SAT LOOP 476 MHz REF STATION REF (EPICS) Gap Loop HVPS + RF CAV TUNER LOOP IQ MOD Klystron 120W Driver - - IQ DEMOD DIRECTLOOP • 15 Stations • 4 LER • 11 HER • 8 Cavities LER • 28 Cavities HER BEAM Slow Loop (EPICS) COMB LOOP Fast Loop (Electronics) 476 MHz Baseband

  8. The PEP-II LLRF LLRF VXI Crate 1.2 MW Klystron Fast Interlock Chassis 120W Klystron Pre-Amplifier Temperature Controlled LLRF “Blue Box” LLRF Station

  9. Insomnia Producing Problems

  10. What Keeps us up at Night Longitudinal Growth Rates Grow Damp measurements in 2003 showed 5-10X greater growth rates than predicted by a linear model.

  11. Longitudinal Growth Rates Previous MAC talks have addressed various ideas we’ve tried which include: Non-Linear Modeling Effort (Claudio Rivetta Talk) Klystron Linearizer (MAC Oct ’06 Talk) Klystron Pre-Amplifiers (MAC Oct ‘06 Talk – Preliminary)

  12. Solution Flow Diagram High Growth Rates Observed Linearizer Project Non-linear Model Comb Rotation Pre-amp Evaluation New Pre-Amps Reduced Growth Rates Observed

  13. Longitudinal Growth Rates Today, I’ll Discuss: Progress since last MAC on: Identifying key parameters and measurements for replacement amplifiers Progress on purchasing and replacement Results of new installations

  14. Pre-Amplifier Specification and Measurements

  15. Klystron Pre-Amplifiers Swept Low Level Carrier Small (network analyzer swept) signal injected along with large carrier to simulate small signal modulation on CW carrier Full Power Carrier

  16. Klystron Pre-Amplifiers Unusual (distorted) response seen when carrier is present Since we use the amplifier with carrier and small signal modulation, the modulation “sees” this response rather than the flat (desirable) response.

  17. Klystron Pre-Amplifiers • Old Data showed LR4-2, HR12-2 and HR12-6 were especially bad in small signal response

  18. Klystron Pre-Amplifiers • LR4-2 Distortion affected ability to implement comb rotation LR42 was nearly unstable with 20 degrees of comb rotation. Simulations show this is due to non-linear pre-amplifier response.

  19. Klystron Pre-Amplifiers Non-linear distortion is also a key parameter of these amplifiers. Rather than use two large tones as is typically done in a TOI measurement, we decided to try a new technique similar to our network analyzer technique. Namely, a small signal in the presence of a large signal.

  20. Klystron Pre-Amplifiers

  21. Klystron Pre-Amplifiers

  22. Klystron Pre-Amplifiers In this case, AmpC was a class A amplifier powered off 240V AC. Amp B was a class AB amplifier powered of 120V. We chose amp B based upon “good enough” performance and much less expensive price

  23. New Pre-Amp Performance In Station

  24. Klystron Pre-Amplifiers STATION REF (EPICS) 476 MHz REF IQ DEMOD Gap Loop ADC + RF CAV IQ MOD Klystron 120W Driver - + - IQ DEMOD DIRECTLOOP DAC BEAM COMB LOOP Built in stimulus driver allows for unique in-situ measurements

  25. Klystron Pre-Amplifiers New Amps installed in all stations

  26. Klystron Pre-Amplifiers

  27. Klystron Pre-Ampliers Since Last October Significant Time spent characterizing and specifying amplifiers in a “new” way. Found Vendor who met specs Bought 17 and installed 15 new pre-amplifiers Amplifiers show much improved response and allow for 20 degrees of comb filter rotation

  28. Longitudinal Growth Rates Conclusions We now feel system is prepared to move to higher current realms in terms of longitudinal growth rates Further work may include: Asymmetric Combs RFP asymmetry calibrations

  29. What else keeps us up? Aborts Biggest Contributors are cavity arcs during startup after down (Heinz S.) We also had many issues with the HVPS systems (things breaking) Things we plan to work on are: PG&E Power Dips (55 Aborts during run 6) LR4-4 Drive Glitches (41 Aborts during run 6)

  30. HVPS Dips

  31. What’s Going On? Constant Running Swing Required of 5W to keep output constant at 900 kW Power can not reach 900 kW and goes over the top For 77 kV @ 900 kW Output, ~24 W Input For 77.5 kV @ 900 kW Output, ~22 W Input For 76.5 kV @ 900 kW Output, ~27 W Input

  32. HVPS Dips What to do? Lower drive power on Klystron Upside: Allows for greater head room More linear running Downside Can’t reach as high power Higher Collector Power

  33. HVPS Dips Since these dips appear to be coming from PG&E, there is very little we can do locally to mitigate them. Constant monitoring of drive set-points will be required For peak currents, we may need to live with the occasional power dip abort

  34. LR4-4 Drive Dips • Ongoing problem since 2005 • AIM HVPS monitor shows noise burst • Followed by Klystron Forward “wiggle” • Followed by very short dropout in drive signal • Followed by beam abort…

  35. LR4-4 Drive Drop Drive mysteriously drops (or rises) Cavity responds after delay

  36. LR4-4 Drive Dips Things Tried so far: Replaced several modules (not well controlled study) Moved drive set point Low trip rate and missing measurement points makes this difficult to diagnose Plans New klystron being installed. Will let run for some time to see if this makes any difference (not likely) Begin plan for swapping various modules. Likely culprits are gap module and RFP module. Will start with one then wait 2-3 weeks, then swap another. Extra Monitoring on HVPS signals to attempt to understand mysterious HVPS noise burst More plans to be developed in LLRF ongoing meetings. This will become high priority.

  37. General Issues

  38. General Ongoing Issues Cavity Tuning Polynomials Polynomial fits for cavity de-tuning vary with temperature Occasionally cavity temperatures have been varied without concern for these polynomials (RF experts not notified) Net result is constant tuning of RF stations as current is pushed. Machine seems to run better after stations are given “tune cavities” and “make polynomials” tune ups. This process take time without beam so administration is reluctant to do except when necessary

  39. General Ongoing Issues Cavity Tuning Polynomials We are working on scheme to make this process run-able by operators. Process must be “bullet proof” Will remind operators to run at opportunistic times when we are without beam for 30 minutes

  40. Summary and Conclusions

  41. Summary and Conclusions Much progress has been made over the last 3-5 years in improving the reliability and performance of the PEP-II RF systems. Some highlights are: Re-designed RFP modules Re-designed IQ&A modules Fixed “Stuck Tuner” Problem Better temperature control on blue boxes Designed new R2 COMB Module (reduced two VXI modules to one) New pre-amplifiers Comb rotation for better beam stability Filters on RE signals Non-linear modeling for low order model longitudinal damping improvement Low Group Delay Woofer for increase low order mode damping Gage Board diagnostics for transverse and longitudinal troubleshooting Matlab GUIs for fault files Matlab GUIs for “tune cavities” and “make polynomials” RF training for operators Model based RF station tuning AIM module diagnostics of HVPS signals SLAC Klystrons in most stations Klystron Linearizer Development Re-designed VXI Clock module Re-designed VXI AIM Module Found & Fixed old VXI COMB stuck overflow problem Upgraded VXI CPU from 40MHz 68040 to 350MHz PPC (and re-designed VXI interface on all old VXI modules) Re-wrote RFP DSP Ripple loop code to reduce phase ripple Added RFP analog ripple loop Found & fixed AC power wiring issue with VXI Crate power supplies, which was causing intermittent problems Upgraded 476Mhz RF Phase Reference System to reduce phase drift and improve stability as well as added more diagnostics Developed full-fledged RF station mock-up in lab for development & troubleshooting Insulated Blue VXI Racks and added heaters with closed-loop control for better temperature regulation Improved RFP Calibration routine Improved IQA calibration method

  42. Summary and Conclusions The PEP-II RF system is running relatively well (2.5 aborts per day) considering the complexity of the overall system. This rate is still too high, but there will be difficulties in reducing this rate due to the lack of “big ticket” aborts to go after. We will (of course) continue working on these issues to the last day of running.

  43. Summary and Conclusions Finally Running at the highest currents will require constant vigilance If we lose a station, we WILL NOT be able to continue running at full current

  44. Acknowledgements Technical Review and Discussions: Dmitry Teytelman, Mike Browne, John Dusatko, Jim Sebek, Ron Akre, Vojtech Pacak, Alan Hill, Kirk Bertsche Original Concept and Design Paul Corredoura, Rich Tighe and Flemming Pedersen Support and Permission Uli Wienands, John Seeman, Mike Sullivan All this work was done under contract #DE-AC02-76SF00515 from the U.S. Department of Energy

  45. The PEP-II RF TEAM High Power RF Alan Hill, Heinz Schwarz, Vojtech Pack, Al Owens, Ron Akre Accelerator Research Department John Fox, Claudio Rivetta, Controls Department Mike Browne, John Dusatko, David Brown, Bill Ross High Voltage Marc Larrus, Dick Cassel, Paul Bellomo, Serge Ratkovsky Control Software Mike Laznovsky Accelerator Dept Mike Sullivan, Uli Wienands, William Colocho, Franz-Josef Decker, Alan Fisher, Stan Ecklund, Mat Boyes, Kirk Bertsche Management John Seeman, Ray Larsen, Sami Tantawi

  46. References Dan Van Winkle – MAC ’06 Talk http://www.slac.stanford.edu/~dandvan/mac_1006_dvwR3.ppt Dan Van Winkle – MAC ’04 Talk http://www.slac.stanford.edu/~dandvan/MAC_12_04.ppt Dan Van Winkle – Internal Linearizer Review http://www.slac.stanford.edu/~dandvan/project_review_3_08_06.ppt Claudio Rivetta et al – PRST Longitudinal Simulation Paper http://prst-ab.aps.org/pdf/PRSTAB/v10/i2/e022801 Dan Van Winkle - EPAC ’06 Klystron Linearizer http://www.slac.stanford.edu/pubs/slacpubs/11750/slac-pub-11945.pdf John Fox – RF Amplifier Selection PAC ’07 http://www.slac.stanford.edu/pubs/slacpubs/12500/slac-pub-12636.pdf Dan Van Winkle – LLRF Workshop 2007 Invited Talk http://www/~dandvan/llrf07.ppt

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