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) LERHER Beam Current3.026 (1.4X)1.96A (2X) RF Voltage4.0516.5 MV # Cavities828 # Klystrons411 (1.8X) Voltage/Cav506590 kV Klystron Pwr755.1845.9kW

5. Current performance and future plans Run 7 Parameters (max planned) LERHER Beam Current4.00(1.9X)2.2A (2.2X) RF Voltage517.5 MV # Cavities828 # Klystrons411 (1.8X) Voltage/Cav625625 kV Klystron Pwr1005980kW

6. Brief Overview of PEP-II RF System

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

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

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 ProjectNon-linear Model Pre-amp Evaluation Comb Rotation 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 Full Power Carrier Swept Low Level Carrier Small (network analyzer swept) signal injected along with large carrier to simulate small signal modulation on CW 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

22. 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 Gap Loop Klystron 120W Driver IQ MOD IQ DEMOD DIRECT LOOP COMB LOOP RF CAV 476 MHz REF STATION REF (EPICS) + - - BEAM + IQ DEMOD DAC ADC 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? For 77 kV @ 900 kW Output, ~24 W InputFor 77.5 kV @ 900 kW Output, ~22 W InputFor 76.5 kV @ 900 kW Output, ~27 W Input Swing Required of 5W to keep output constant at 900 kW Constant Running Power can not reach 900 kW and goes over the top

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. 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.ppthttp://www.slac.stanford.edu/~dandvan/mac_1006_dvwR3.ppt Dan Van Winkle – MAC ’04 Talk –http://www.slac.stanford.edu/~dandvan/MAC_12_04.ppthttp://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.ppthttp://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/e022801http://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.pdfhttp://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.pdfhttp://www.slac.stanford.edu/pubs/slacpubs/12500/slac-pub-12636.pdf Dan Van Winkle – LLRF Workshop 2007 Invited Talk –http://www/~dandvan/llrf07.ppthttp://www/~dandvan/llrf07.ppt