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PREX Main<< Information for Shift Takers << Shift Leader << HOW TOs

If a lead target has not already been commissioned, this run plan is incomplete. In this case, an expert is needed. For commissioned targets, there is a fast way, and a slow way. To protect targets, the default is to do it the slow way. Use the fast way only when instructed to by the run coordinator or a similar expert.

Fast way: for well known targets and running conditions (someone will get fired if they don't check quad settings before doing this).

  1. verify the raster is on by looking at the scope. Verify that nominal raster settings and nominal beam positions are being used
  2. with the target out or the current at 1uA, perform a "high current spot++". Check the raster, as visualized by the bpms, is the same size as previous high current spot measurements in the logbook.
  3. if this passes the check (and an expert has checked quad settings and is willing to gamble with the target) then you are good to go!

Slow way: this is the only right way to do it. For a lead target that is already known and commissioned:

  1. Check if the raster has been measured for the particular beamline quadrupole settings in use now. See "how to check if raster has been measured for these beam optics" (to be written)
    • If the raster size has already been measured, then you can use the previously used raster specification in "MCC units" that correspond to this set of quadrupole setpoints.
    • If you ask for 12 x 7.2 mm raster to give the correct spot size, this requires that the quad settings on the beamline have not changed. Check that the quadrupole settings are the same as ever.
    • If the raster size has not been measured for this specific set of quadrupole settings, you must measure the raster size with the 90-degree carbon hole.
  2. Measure the raster size with the 90-degree carbon hole
    1. With no target, establish 2uA beam. Turn off FastFeedback.
    2. With no target and 2 uA beam. Move beam to center on the collimator, which is now the same as the carbon hole center: bpm1H04a (x,y) = (0,0), bpm1H04e (x,y) = (0.6, 0.4)mm. Record the cavbpm4b and cavbpm4d readbacks at this location. (The cavity bpms will continue to work at very low current)
    3. turn off beam. (do not change correctors, and be sure target lock is turned off, so beam will recover to same location).
    4. verify that VDC and GEM detector HV are off
    5. Move in C-hole 90deg target.
    6. turn on 20 nanoAmp beam. (At the present time, this corresponds to MCC using an attenuator setting = 107. If you have doubts, you can always ask MCC to use Faraday Cup#2 to find an attenuator setting for approximately 20 nA.)
    7. Record the cavbpm4b and cavbpm4d readbacks at this location. (The cavity bpms will continue to work at very low current)
    8. Set raster to the "MCC units" listed on the white board.
    9. run spot++. verify that raster (4mm x 6mm is desired in reality) is (approximately) appropriately filled by the 2mm diameter hole. If not, tune the MCC setpoints until the raster size scale matches the dimensions for the 2mm diameter hole. (it may not "look" round, but the horizontal and vertical dimensions should both match a 2mm diameter hole).
  3. Prepare beam for Lead target
    1. remove the C-hole target
    2. establish 1 uA beam (with no target)
    3. move beam to collimator center 4A(x,y) = (0,0) and 4E(x,y) = (0.6, 0.4)mm.
      • Record the cavbpm4b and cavbpm4d positions.
    4. turn beam off
    5. set raster to 10x10 (MCC units)
  4. Move to lead target
    1. verify that VDC and GEM detector HV are off
    2. mask and insert lead target
    3. establish 20 nanoAmp beam. (Again, at present, this is an attenuator setting of 107.)
    4. run spot++. Verify no edges.
    5. Set raster to nominal size. (presently 6mm width and 7mm height).
    6. run spot++ (this allows us to check the uniformity of the lead).
    7. turn off S0 voltages on left and right arms.
    8. set to desired current. No more than 50uA. But keep an eye on the whiteboard, we may be increasing this limit over time.
      • WATCH target temperatures, target return coolant temperature, collimator temperature, and beamline thermocouples.