General How-to

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Beam Restoration

Restoring Beam after Short Downtime

  • Ask for 5 nA beam current and check the 2C24A and 2H01 beam (x, y) positions against the Reference Values (tab "Short Term Schedule") after

Beam Tuning to Tagger Dump

◊ Make sure the BMT along FMT is in SAFE mode, SVT HV is OFF, (LV is ALWAYS ON), and all other CLAS12 detectors HV are OFF.
  • A few points to note:
• Change the beam type to "Photon" from the "BTA Config"
• Ask MCC to energize the tagger magnet
• Move the collimator to the Blank position after the tagger is energized
• Ask MCC to mask the beam halo counters (FSDs: Upstream, Midstream, Downstream, BOM)
• Ask MCC for 5 nA beam current and make sure the Orbit Locks are OFF;
• Check the 2C21A and 2C24A beam positions (x, y) against the Reference Values (tab "Short Term Schedule")
- If the beam positions are OFF, ask MCC to bring them to the reference values.
• In case the two BPMs (x, y) positions look good, take a harp scan (HS) at Harp 2C21 (Upstream Right Counter) and Tagger Harp (2C24; Upstream Right Counter):
- It should be noted that the beam must be ON during the scan. Once OFF, abort and restart once the beam is back.
- Compare the results with the HS References (tab "Short Term Schedule") and bear in mind that the fit ranges might need to be adjusted manually to assess the fit results;
- If good, log the new scan results.

Møller run

Follow the standard procedure as described in the manual Performing Møller Runs.

A few points to note:

  • Request 20 nA , Orbit Locks should be OFF;
  • The BPMs 2C21 and 2C24A may be out of range after the Møller configuration.
  • Keep running until the polarization uncertainty is < 1.5%

Beam Tuning to Faraday Cup

Study the manual: Establishing Physics-Quality Beam, and take into account the first steps mentioned therein. This is typically done after tuning to the tagger dump (and possibly taking a Moller run).

  • A few points to note:
    • Change the beam type to "Electron";
    • Ask MCC to de-energize the tagger magnet, which includes degaussing the tagger magnet and turning the power supply OFF;
    • Ask the operator to use the script only, not try it by hand, as this might trip the circuit breaker of the tagger magnet power supply.
    • (If initial beam tune, target should be "Empty")
    • Make sure the Beam Blocker is OUT
    • Move the collimator to the 20 mm position
    • Ask MCC to unmask beam halos
    • Set the halo counter FSD thresholds to 1 MHz and the integration time interval to 50 milliseconds
    • Insert the Downstream Viewer, Chromax, in the beamline
    • Ask MCC for 5 nA beam current
      • If the 2C24A and 2H01 beam positions are OFF, ask MCC to bring them to the reference values (see tab Short_Term_Schedule)
      • In case the BPM (x, y) positions look good, take a harp scan at 2H01 (Midstream Left)
      • The beam must be ON during the scan. Once OFF, abort and restart once the beam is back
      • Compare the results with the harp scan references (see tab Short_Term_Schedule)
      • If good, log the new scan results.
  • Once done and before resuming the production data-taking:
    • Retract the Downstream Viewer from the beamline;
    • Put the FSDs thresholds and integration time to their reference values;
    • Turn all detector HV ON, for MVT "HV ON - Full Voltage";
    • MCC might need to adjust the beam positions after going to the production beam current.
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