RF System Improvements for Performance and Reliability Dan Van Winkle Kirk Bertsche, John Fox,...
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Transcript of RF System Improvements for Performance and Reliability Dan Van Winkle Kirk Bertsche, John Fox,...
RF System Improvements for Performance and Reliability
Dan Van WinkleKirk 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
• General ongoing global issues
• Conclusions and Outlook
Current and Planed Performance
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
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 1005 980 kW
Brief Overview of PEP-II RF System
The PEP-II LLRF
Gap Loop
SAT LOOP
HVPS
Klystron120W Driver
IQ MOD
IQ DEMOD
DIRECTLOOP
COMB LOOP
RFCAV
476 MHzREF
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
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
Insomnia Producing Problems
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.
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)
Solution Flow Diagram
High Growth Rates Observed
Linearizer Project Non-linear Model
Pre-amp EvaluationComb Rotation
New Pre-Amps
Reduced Growth Rates Observed
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
Pre-Amplifier Specification and Measurements
Klystron Pre-Amplifiers
Full Power Carrier
Swept Low Level CarrierSmall (network analyzer swept) signal injected along with large carrier to simulate small signal modulation on CW carrier
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.
Klystron Pre-Amplifiers
• Old Data showed LR4-2, HR12-2 and HR12-6 were especially bad in small signal response
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.
Klystron Pre-AmplifiersNon-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.
Klystron Pre-Amplifiers
Klystron Pre-Amplifiers
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
New Pre-Amp Performance In Station
Klystron Pre-Amplifiers
Gap Loop
Klystron120W Driver
IQ MOD
IQ DEMOD
DIRECTLOOP
COMB LOOP
RFCAV
476 MHzREF
STATION REF (EPICS)
+
-
-
BEAM
+
IQ DEMOD
DAC
ADC
Built in stimulus driver allows for unique in-situ measurements
Klystron Pre-Amplifiers
• New Amps installed in all stations
Klystron Pre-Amplifiers
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
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
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)
HVPS Dips
Pout vs. Pin
600
650
700
750
800
850
900
950
1000
1050
1100
0 10 20 30 40 50 60 70
Pin (W)
Po
(k
W)
77 kV
77.5 kV
76.5 kV
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
Pout vs. Pin
600
650
700
750
800
850
900
950
1000
1050
1100
0 10 20 30 40 50 60 70
Pin (W)
Po
(k
W)
75.5 kV
76 kV
75 kV
Constant Running
Power can not reach 900 kW and goes over the top
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
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
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…
LR4-4 Drive Drop
• Drive mysteriously drops (or rises)
• Cavity responds after delay
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.
General Issues
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
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
Summary and Conclusions
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
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.
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
Acknowledgements
Technical Review and Discussions:Dmitry Teytelman, Mike Browne, John Dusatko, Jim
Sebek, Ron Akre, Vojtech Pacak, Alan Hill, Kirk Bertsche
Original Concept and DesignPaul Corredoura, Rich Tighe and Flemming Pedersen
Support and PermissionUli Wienands, John Seeman, Mike Sullivan
All this work was done under contract #DE-AC02-76SF00515 from the U.S. Department of Energy
The PEP-II RF TEAMHigh 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
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