Zero field controller (HIFI)

The zero field controller on HIFI follows a similar design to the zero field controller used on other instruments such as EMU and MuSR, but is implemented as a separate IOC, ZFHIFI, due to a number of differences.

The main differences are:

  • There are 6 field probes, across 2 magnetometer devices (each an instance of a Group3 hall probe, G3HALLPR).

    • There is HIFI-specific field correction logic used to get a corrected field from these 6 probes

  • The zero field system on HIFI uses the shim coils from the HIFI cryomag as it’s outputs. These are CRYOSMS_02..CRYOSMS_04, hosted on hifi-cryomag

Expected setup

The expected setup for this system is:

  • CRYOSMS IOCs on HIFI-CRYOMAG for the shim coils, configured with:

    • "CRYOMAGNET": "No" (The shim coils should not be set up as a cryomagnet)

    • "NON_PERSISTENT_SETTLETIME": 0 (To avoid excessive settle times on ZF writes)

    • "HOLD_TIME": 0 (To avoid excessive settle times on ZF writes)

    • "HOLD_TIME_ZERO": 0 (To avoid excessive settle times on ZF writes)

  • G3HALLPR IOCs on NDXHIFI configured with:

    • "FIELD_SCAN_RATE": "Passive" (the zero-field system will scan these when relevant)

    • "FLNK0": "IN:HIFI:ZFHIFI_01:MAGNETOMETER:X1:READINGS_UPDATED.PROC CA" (and similar for flnk1/2)

  • ZFHIFI_01 configured with:

    • "PSU_X": f"IN:HIFI-C11:CRYOSMS_02" (and similar for PSU_Y/PSU_Z)

    • "MAGNETOMETER_X1": f"IN:HIFI:G3HALLPR_01:0"

    • "PSU_X_MIN": -15 (and similar for Y&Z, and MIN/MAX)

The flow of control is:

  • The ZFHIFI ioc will request the magnetometers to take readings by processing G3HALLPR:...:TRIGGER

  • The G3HALLPR ioc will take a reading

  • The G3HALLPR ioc will process the READINGS_UPDATED pv on the ZFHIFI ioc

  • When all probes are ready, the zero-field ioc will calculate corrected fields

  • The zero-field controller will write a new setpoint to the cryosms IOCs

  • The cryosms IOCs will ramp the fields on the shim coils using it’s internal state-machine

  • The zero-field controller will wait for the cryosms to be “within tolerance” of the setpoint and reporting READY status.