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:
- Run an SSA calibration
- Tune a cavity to resonance (a detune of 0Hz)
- Characterize the cavity and calculate the probe Q
- 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
Full Procedure
SSA Calibration
- Set the drive max to the previously saved drive max found during initial cavity commissioning (or 1 for the the harmonic linearizers)
- Recursively run an SSA calibration with decreasing drive max until either the calibration succeeds or it hits one of two fault conditions:
- The max forward power is less than 3kW
- The desired drive max is less than 0.5
Tune to Resonance
- Enable the piezo
- Set the piezo to manual
- Set the piezo DC voltage offset to 0
- Set the piezo bias voltage to 25V
- Set the RF drive level to 15%
- Set the RF mode to chirp
- Find a chirp range that yields a valid detune
- If no valid detune found and chirp range exceeds 500000Hz, throw an error
- Set TUNE_CONFIG PV to Other (indicating that the cavity is at an intermediate state)
- Estimate the (micro)steps to resonance using an empirically found steps per hz from initial cavity commissioning
- Currently 256/1.4 for 1.3GHz cavities and 256/18.3 for 3.9GHz cavities
- 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
- Throw an error if the total number of steps moved exceeds the original estimate by 10% (this could indicate the motors disengaging)
- Set TUNE_CONFIG PV to On Resonance
Cavity Characterization
- Set the pulsed drive level to 15%
- Run a cavity characterization
- Raise an error if the characterization crashed
- Raise an error if the loaded Q is not within 2.5e7 and 5.1e7
- Raise an error if the cavity scale factor is not within 10 and 125
- Push the loaded Q and cavity scale factor
- Reset the data decimation to 255 for both CW and pulsed
- Reset the piezo feedback set point to 0
- Run the cavity probe Q calculation
Cavity Ramp-Up to ADES
- Set the piezo to feedback
- Set the RF mode to SELA
- If the cavity is off, set the amplitude to 5MV and turn it on
- Walk the amplitude in steps of 0.5MV up to 10MV and steps of 0.1MV above 10MV
- Raise an error if the quench interlock is latched
- Set the RF mode to SELAP