General How-to

Beam Restoration

• Study the manual: Establishing Physics-Quality Beam. If you do not feel confident to do this by yourself, contact the Beamline Expert.

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 (at the bottom of Short Term Schedule tab) whenever

• there is a beam steering or a change in its orbits;

• the beam current is changed; e.g., after a target change;

• BPMs 2C21A and 2H01 positions are off, i.e., they are not within +/-0.1 mm. If so, ask MCC to bring them to the reference values recorded at the bottom of Short Term Schedule tab.

Beam Tuning to Tagger Dump

• Study the manual: Establishing Physics-Quality Beam, and take into account the first steps mentioned therein.

◊ 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 to avoid getting an alarm;

• 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 (at the bottom of Short Term Schedule tab);

- 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 at the bottom of Short Term Schedule tab 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

• Check its manual: Performing Møller Runs:

• Must be noted that the manual has not been updated since the last run period. However, the underlying script in the Møller GUI should do it all for you.

• After "reconfigure" and "enter," ask MCC for 5 nA and make sure the Orbit Locks are still OFF;

- The BPMs 2C21 and 2C24A may become out of range after the Møller configuration. That is fine, so don't ask MCC to adjust it to the reference values, as that will mess up the positions after exiting the Møller configuration.

• Start the run and keep it running until the polarization uncertainty reaches 1.5%, then end the run and log its results after entering your username.

• Exit the Moller configuration.

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.

• Make sure the Beam Blocker is OUT of the beamline.

• Move the collimator to the 20 mm position;

• Ask MCC to unmask beam halos;

• Insert the Downstream Viewer in the beamline;

• Ask MCC for 5 nA beam current;

• Check the 2C24A and 2H01 beam positions (x, y) against the Reference Values (at the bottom of Short Term Schedule tab);

- 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 at 2H01 (Midstream Left):

- 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 at the bottom of Short Term Schedule tab;

- If good, log the new scan results.

• Once done and prior resuming the production data-taking:

• Retract the Downstream Viewer from the beamline;

• Turn all detectors HV ON and make sure the MVT is switched to "HV ON - Full Voltage";

• Proceed with production as instructed in Short Term Schedule tab:

- Keep in mind that MCC might need to adjust the beam positions after going to the production beam current.