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Introduction

The need for automating SRF cavity run up arose from the human error involved in manually implementing a long list of clearly defined steps. 

The basic procedure is:

  1. Run an SSA calibration
  2. Tune a cavity to resonance (a detune of 0Hz)
  3. Characterize the cavity and calculate the probe Q
  4. Ramp the RF to the desired amplitude (ADES)


Full source code can be found here. It can be run natively on unix systems using the Local PyDM/Simulacrum Setup instructions

Pseudocode Walkthrough

SSA Calibration

  1. Set the drive max to the previously saved drive max found during initial cavity commissioning (or 1 for the the harmonic linearizers)
  2. Recursively run an SSA calibration with decreasing drive max until either the calibration succeeds or it hits one of two fault conditions:
    1. The max forward power is less than 3kW
    2. The desired drive max is less than 0.5

Auto Tune

  1. Enable the piezo
  2. Set the piezo to manual
  3. Set the piezo DC voltage offset to 0
  4. Set the piezo bias voltage to 25V
  5. Set the RF drive level to 15%
  6. Set the RF mode to chirp
  7. Find a chirp range that yields a valid detune
    1. If no valid detune found and chirp range exceeds 500000Hz, throw an error
  8. Set TUNE_CONFIG PV to Other (indicating that the cavity is at an intermediate state)
  9. Estimate the (micro)steps to resonance using an empirically found steps per hz from initial cavity commissioning 
    1. Currently 256/1.4 for 1.3GHz cavities and 256/18.3 for 3.9GHz cavities
  10. While the detune is outside of the piezo capture range (50Hz), recalculate the steps to resonance and send 90% of that value to the stepper motor
    1. Throw an error if the total number of steps moved exceeds the original estimate by 10% (this could indicate the motors disengaging)
  11. Set TUNE_CONFIG PV to On Resonance

Cavity Characterization

  1. Set the pulsed drive level to 15%
  2. Run a cavity characterization
    1. Raise an error if the characterization crashed
    2. Raise an error if the loaded Q is not within 2.5e7 and 5.1e7
    3. Raise an error if the cavity scale factor is not within 10 and 125
  3. Push the loaded Q and cavity scale factor
  4. Reset the data decimation  to 255 for both CW and pulsed
  5. Reset the piezo feedback set point to 0

Cavity Ramp-Up

  1. Set the piezo to feedback
  2. Set the RF mode to SELA
  3. If the cavity is off, set the amplitude to 5MV and turn it on
  4. Walk the amplitude in steps of 0.5MV up to 10MV and steps of 0.1MV above 10MV
    1. Raise an error if the quench interlock is latched
  5. Set the RF mode to SELAP


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