Piezo Studies and Temperature Measurements

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Piezo Studies and Temperature Measurements

• Ruben Carcagno
• May 11, 2005

2
Background

• Fast tuners (e.g., piezo tuners) are needed to
  maintain high RF power efficiency in high
  gradient (e.g., 35 MV/m) SCRF cavities
• Key component for cost reduction of ILC and
  Proton Driver
• FNAL piezo tuner studies were done for the 3.9
  GHz CKM deflecting cavity at A0.
• Experience and results are transferable to 1.3
  GHz cavities for the ILC and Proton Driver. RD
  in these areas will continue at HPTF.

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Detuning and RF Power

• RF power increase for field control due to
  detuning

?f cavity detuning (Hz) f1/2 cavity
bandwidth 200 Hz for 1.3 GHz TESLA
cavities 65 Hz for 3.9 GHz CKM
cavities

• Detuning highly sensitive to small changes in
  cavity shape
• Example 13-cell, 3.9 GHz CKM cavity (from FEA)

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Detuning Sources

• Fast, small changes in cavity shape are caused by
  two primary sources
• Lorentz Forces (electromagnetic)
• Important for pulsed operation, high gradients
  (e.g., 35 MV/m)
• Highly repetitive
• Main detuning concern for ILC and Proton Driver
• Piezo compensation demonstrated at the Tesla Test
  Facility
• Microphonics (vibration sources)
• Important for cw operation, narrow bandwidth
• Random
• Microphonics compensation less advanced than
  Lorentz
• FNAL work at A0 contributed to advances in the
  state of the art of microphonics detuning
  compensation

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Detuning Compensation Fast Tuners
Fast tuners have been proposed for active
detuning control by applying a counteracting
force to the cavity

• PIEZOELECTRIC ACTUATORS
• Commercially available from multiple sources
• Typically used at room temperature
• Work at cryogenic temperatures with reduced
  stroke. Characterization important
• Actuator of choice in other labs for detuning
  compensation studies

• MAGNETOSTRICTIVE ACTUATORS
• Being introduced as an alternative to
  piezoelectric actuators for SCRF fast tuning
• Newer technology for this application, single
  source
• Some labs are investigating this option

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Studies at 1.8 K3-cell 3.9 GHz CKM cavity

• Microphonics Spectrum with pumps ON and OFF
• Vibration measurements with piezo as a sensor
• Piezo-RF detuning transfer function
• Manual microphonics detuning piezo compensation
• Quench and hot spot location using thermometry

Temperature Rings
Piezo Actuator P-206-40 from Piezosystem Jena
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Manual Detuning Compensation

• Cavity system support was not optimized to
  minimize microphonics
• Microphonics spectrum shows a strong detuning
  frequency at 30 Hz
• Detuning compensation at 1.8 K was attempted by
  manually adjusting the piezo frequency,
  amplitude, and phase
• Detuning was reduced by more than a factor of
  three and maintained for several seconds
• The result was reproducible, showing the
  feasibility of using a piezo actuator to
  compensate microphonics detuning

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Studies at Room TemperatureAutomatic
Microphonics Detuning Compensation
Piezo

• Automatic compensation with an adaptive
  feedforward control method demonstrated in a
  13-cell CKM cavity at room temperature.
• For details, see
• R. Carcagno, L. Bellantoni, T. Berenc, H.
  Edwards, D. Orris, A. Rowe, Microphonics
  Detuning Compensation in 3.9 GHz Superconducting
  RF Cavities, 11th Workshop on RF-Superconductivit
  y SRF 2003.

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Detuning Compensation Results

• Automatic compensation demonstrated for three
  induced frequencies (15 Hz, 27 Hz, and 45 Hz)
• More than 20 dB attenuation
• Mechanical Resonances quickly identified by
  driving piezo with white noise

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Piezo RD Next StepsILC and Proton Driver
Support
Capture Cavity 2 Tuner

• Piezo RD will continue with the HPTF Capture
  Cavity 2 test
• Integrate piezo with cavity tuner
• Start with DESY design
• Studies at 2 K for ILC and Proton Driver
• Lorentz detuning compensation
• Microphonic detuning compensation
• Piezo characterization and reliability under
  operating conditions
• Integrate piezo control with LLRF controls
• Evaluate Alternatives (e.g., magnetostrictive
  actuators)
• Increase collaboration efforts with other Labs
  and institutions (e.g., DESY, ANL, JLab, Saclay,
  etc)

Two Piezos

• Challenges
• Piezo mechanical integration with tuner (preload,
  reliability)
• Mechanical resonances (complicate control
  algorithms)
• Cost/space reduction for mass production and
  industrialization (power amplifiers, piezo size)

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Fast Cavity Thermometry
New system based on smaller CERNOX sensors was
developed at FNAL Fast (10 kHz) temperature
acquisition rate to study quench evolution

• Traditional Carbon Glass RTDs used in SCRF
  thermometry (e.g., Cornell system) too large for
  small 3.9 GHz CKM cavity geometry

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Thermometry Results

• Quench location clearly identified
• Hot spot shifts 90 degrees with cw polarization
  mode
• Increasing RF power resulted in quench at hot
  spot location

Lambda point
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Conclusions

• FNAL has already begun developing expertise in
  areas of piezo tuning and cavity thermometry
• RD in these areas has resulted in advances in
  microphonics detuning compensation and the
  ability to pinpoint quench location in small
  cavities
• The focus of this work is now shifting towards
  ILC and Proton Driver support
• Piezo tuning development work will continue with
  the HPTF Capture Cavity 2 test
• Fast tuning (e.g., piezo) capability is critical
  for cost reduction efforts in high gradient SCRF
  machines (high RF power efficiency)