Compton Photon Detector Centering Procedure

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Spring 2019 Compton Photon Detector Commissioning

  • Before MCC begins the initial process of passing bream through the Chicane, we must:
    1. Check and set HV:
      • PhDet HV -> OFF
      • Side (V) and Top (H) Finger Scintillator -> ON
      • Laser table scintillators -> ON
    2. The following EPICS channels may be useful to monitor the backgrounds
      • ComptonUSbg1
      • ComptonUSbg2 <-- It's possible this one is unplugged
      • ComptonDSbg1
      • ComptonDSbg2
    3. The following EPICS values may also be useful
      • hac_bcm_average
      • IPM1P02A.XPOS
      • IPM1P02A.YPOS
      • IPM1P02B.XPOS
      • IPM1P02B.YPOS
      • Optionally the two finger scintillators may be useful, though it's likely they won't see anything if they are behind the collimator
        • ComptonHfingerRate
        • ComptonVfingerRate
    4. It may be useful to take a run during this period. Even though the HV on the detector is off, we may use it to study noise on the system.
  • After the beam is stable in the chicane and ready to center beam on laser
    1. Check and set HV:
      • PhDet HV -> ON
      • Side (V) and Top (H) Finger Scintillator -> ON
    2. Start a Compton Run (though, no need to analyze the run right now, this will just help us commission and calibrate the DAQ later)
    3. With the laser ON and 'not flipping, monitor the following EPICS channels:
      • IPM1P02A.YPOS
      • IPM1P02B.YPOS
      • ComptonCentralRate
      • ComptonCentralRateHigh
      • COMPTON_PW1PCAV_ca
    4. As the beam is scanned vertically monitor for spikes in ComptonCentralRate and ComptonCentralRateHigh.
      • The goal is to maximize ComptonCentralRate (assuming stable beam and laser power) and record the vertical position
      • Ideally we would like the slope between BPM 02A and 02B to be as close to zero as possible
  • After the beam is centered on the laser, ask MCC to lock the beam in the optimal position found previously and then begin the detector centering procedure
    1. Check and make sure all HV Compton channels HV_Control_GUI are ON (should have been done by steps above, so just confirm nothing has tripped off)
    2. Start a new run
    3. Center the detector vertically (Note: do not lower the table to 0, always keep it above 0 mm)
      1. Set the Photon Detector table to X=69.00 mm, Y=6.00 mm
      2. Monitor EPICS channels:
        • ComptonHfingerRate <-- looking for a maximum/peak on this when scanning table position
        • COM_DETPH_YCPOSai
        • ComptonCentralRate <-- possibly should see a minimum on this channel
        • ComptonCentralRateHigh <-- possibly should see a minimum on this channel
      3. Then in 0.5 mm increments scan Y from 6.00 to 16.00 mm (~2-3 seconds at a time is enough)
      4. Once a rough idea of where the max was, scan a range in as small increments as possible with a +/- 2mm range
      5. Once you confirm the optimal y-position that gives maximum ComptonHfingerRate maximum (and minimum on ComptonCentralRate and ComptonCentralRate) , then move the table up by 20 mm from this position.
    1. Center the detector horizontally (Note: do not lower the table to 0, always keep it above 0 mm)
      1. Set the Photon Detector table to X=44.00 mm, Y=<value from step above>
      2. Monitor EPICS channels:
        • ComptonVfingerRate <-- looking for a maximum/peak on this when scanning table position
        • COM_DETPH_YXPOSai
        • ComptonCentralRate <-- possibly should see a minimum on this channel
        • ComptonCentralRateHigh <-- possibly should see a minimum on this channel
      3. Then in 0.5 mm increments scan Y from 44.00 to 54.00 mm (~2-3 seconds at a time is enough)
      4. Once a rough idea of where the max was, scan a range in as small increments as possible with a +/- 2mm range
      5. Once you confirm the optimal y-position that gives maximum ComptonVfingerRate maximum (and minimum on ComptonCentralRate and ComptonCentralRate) , then move the table in +x direction by 20 mm from this position.