Introduction:

Each cavity's LLRF system monitors various values and input bits that it uses as interlocks to turn off the cavity. If a cavity interlock trips, operators should CATER the issue, attempt to reset the interlock, and contact the area physicist if it doesn't reset. As always, please keep track of interlock trips and subsequent actions via the elog. 

Controls

Go to LCLSHome → LxB/RF → Cavity Control and select a cryomodule from the dropdown. Click the "More..." button next to the cavity you want to see the Cavity Overview screen, the top part of which is in the following figure: 

SC LLRF Overview screen.png

On this screen in the middle-upper right is a section labeled "Interlocks" which shows the status for the interlocks. The Current column shows if that interlock is currently faulted and the Latched column shows if the interlock has faulted but not been reset. There's a reset button at the bottom of that section that sends a reset to the four cavities controlled by that Resonance/Interlock chassis.

If you select "Interlocks" button at the top, you get the following display:

SC LLRF Ilock screen.png

Interlocks

In the left column are the interlocks input to the Resonance/Interlock chassis:

  • Stepper Temp
    • This indicates that the tuner stepper motor temperature is out of range. If the stepper motor temperature is too high, it could indicate a problem with the tuner or the thermal strapping of the motor. A hot motor could transmit heat to the cavity causing a quench.
    • How to set range (done only with area physicist approval):
      • If you click Temperatures in the lower right, you get a screen that allows you to set the low and high limits (in volts) for the interlock.
  • Coupler Temp 1 & 2
    • This indicates that a coupler thermal sensor detects a temperature out of range. If the coupler is too warm, this could indicate a problem with the coupler (wrong Qext) or with the coupler's thermal strapping.
    • How to set range (done only with area physicist approval):
      • If you click Temperatures in the lower right, you get a screen that allows you to set the low and high limits (in volts) for the interlock.
  • Coupler Vacuum
    • This is the a fault indication from the vacuum system to the LLRF system when the combination gauge on the coupler manifold exceeds the given limit.
    • How to set trip threshold (done only with area physicist approval)
      • Presumably this is within the vacuum system.
  • Beamline Vacuum
    • This is the a fault indication from the vacuum system to the LLRF system when the beamline vacuum exceeds the given limit. It would be nice if the vacuum system said which gauge it was using. Presumably the nearest one?
    • How to set trip threshold (done only with area physicist approval)
      • Presumably this is within the vacuum system.
  • Cryo Summary
    • Not sure what this is just yet. An input from the CM cryo system to the LLRF system is planned. Liquid level too low? Pressure too high? Those would be nice.
    • Response: If the liquid level or pressure is out of spec, you can't run RF until it is within spec. Contact area physicist and start digging into archived values to try to figure out what went wrong. Solution might be to wait until the system re-equilibrates or (not likely) with area physicist approval and if you have the headroom, park all the cavities and follow procedure before recovering beam.


On the right you see a summary of the Resonance/Interlock Chassis' interlock as an input to the RF Station interlock AND which also includes:

  • FPGA PLL Lock
    • This detects a temporary loss of externally supplie LO for the onboard clock which no longer guaranteees the LLRF digital clock is locked to the accelerator.
    • Short term fix is to re-run the rack checkout to synchronize the clock. If the problem persists, then LLRF experts need to investigate the LO level into the chassis.
  • EPICS IOC Watchdog
    • If the watchdog detects that the IOC is down, it trips the interlock.
    • Bug a LLRF expert (Andy, Sonya) for appropriate response.
  • Resonance/Interlock Link
    • This trips if a problem is detected in the communication link between the RF Station Chassis and the Resonance/Interlock Chassis.
    • Bug a LLRF expert (Andy, Sonya) for appropriate response.
  • SSA Permit
    • This trips if the SSA isn't ON and happy. Appropriate response is to go to the SSA screen from the Overview display ("More SSA..." in upper left section and the subsequent Expert... screen if needed), identity why the SSA tripped, attempt a Fault Reset. If it resets and turns on without issue, CATER to RF group and put a note in elog explaining what faults were seen. If it trips immediately, park the cavity following the Cavity Parking procedure BUT NEED HELP HERE which includes steps to CATER the problem and making elog entries.
  • Quench
    • This trips if the measured power in the cavity is less than expected given the forward power measured at the input waveguide.
    • Quench response procedure is forthcoming. Bug the area physicist or your nearest SRF Group member when next you see them.
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