RF%20System%20Improvements%20for%20Performance%20and%20Reliability

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

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• Current and Planed Performance

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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

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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

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• Brief Overview of PEP-II RF System

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The PEP-II LLRF
STATION REF (EPICS)
SAT LOOP
476 MHz REF
Gap Loop
STATION REF (EPICS)
HVPS

RF CAV
TUNER LOOP
Klystron
IQ MOD
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
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The PEP-II LLRF

• LLRF Station

LLRF VXI Crate
1.2 MW Klystron
Fast Interlock Chassis
120W Klystron Pre-Amplifier
Temperature Controlled LLRF Blue Box
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• Insomnia Producing Problems

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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.

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Longitudinal Growth Rates

• Previous MAC talks have addressed various ideas
  weve tried which include
• Non-Linear Modeling Effort (Claudio Rivetta Talk)
• Klystron Linearizer (MAC Oct 06 Talk)
• Klystron Pre-Amplifiers (MAC Oct 06 Talk
  Preliminary)

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

• Today, Ill Discuss
• Progress since last MAC on
• Identifying key parameters and measurements for
  replacement amplifiers
• Progress on purchasing and replacement
• Results of new installations

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• Pre-Amplifier Specification and Measurements

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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
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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.
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Klystron Pre-Amplifiers

• Old Data showed LR4-2, HR12-2 and HR12-6 were
  especially bad in small signal response

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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.
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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.
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Klystron Pre-Amplifiers
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Klystron Pre-Amplifiers
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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
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• New Pre-Amp Performance In Station

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Klystron Pre-Amplifiers
STATION REF (EPICS)
476 MHz REF
IQ DEMOD
Gap Loop
ADC

RF CAV
Klystron
IQ MOD
120W Driver
-

-
IQ DEMOD
DIRECTLOOP
DAC
BEAM
COMB LOOP
Built in stimulus driver allows for unique
in-situ measurements
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Klystron Pre-Amplifiers

• New Amps installed in all stations

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Klystron Pre-Amplifiers
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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

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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

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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
• PGE Power Dips (55 Aborts during run 6)
• LR4-4 Drive Glitches (41 Aborts during run 6)

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HVPS Dips
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Whats 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 _at_ 900 kW Output, 24 W Input
For 77.5 kV _at_ 900 kW Output, 22 W Input
For 76.5 kV _at_ 900 kW Output, 27 W Input
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HVPS Dips

• What to do?
• Lower drive power on Klystron
• Upside
• Allows for greater head room
• More linear running
• Downside
• Cant reach as high power
• Higher Collector Power

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HVPS Dips

• Since these dips appear to be coming from PGE,
  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

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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

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LR4-4 Drive Drop

• Drive mysteriously drops (or rises)
• Cavity responds after delay

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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.

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• General Issues

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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

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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

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• Summary and Conclusions

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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 IQA 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

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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.

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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

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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

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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

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References

• Dan Van Winkle MAC 06 Talk
• http//www.slac.stanford.edu/dandvan/mac_1006_dvw
  R3.ppt
• Dan Van Winkle MAC 04 Talk
• http//www.slac.stanford.edu/dandvan/MAC_12_04.pp
  t
• Dan Van Winkle Internal Linearizer Review
• http//www.slac.stanford.edu/dandvan/project_revi
  ew_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/s
  lac-pub-11945.pdf
• John Fox RF Amplifier Selection PAC 07
• http//www.slac.stanford.edu/pubs/slacpubs/12500/s
  lac-pub-12636.pdf
• Dan Van Winkle LLRF Workshop 2007 Invited Talk
• http//www/dandvan/llrf07.ppt