Beam Recovery

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PREX Main<< HOW TOs << Expert Tools


  • 1. Make sure we are centered on beam collimator so we don't destroy it.
  • 2. Ideally that BPM position is also compatible with not hitting the copper frame of the Pb/D target. Need to check.
  • 3. Rastered beam should be big enough to spread heat and not melt the target, and also at least 3 mm from copper frame. (scatter from Cu would be a ruinous background.)


  • The "MCC units" of raster is what they set and what is displayed in the Raster GUI.
  • The "observed" raster size is what is displayed by spot_L. It's different because of quad optics.
  • Make sure you understand the difference. We care about the observed size, but we communicate to MCC by telling them in their units.

PREX I procedure

Procedure for Long Beam Down

Check if the septum on !!

Make sure we have Tune P. (If someone has turned off HRS magnets they may not come back in right state.)

  1. Empty target, establish correct beam position Check beam position
    • 1 uA empty target
    • BPM4A (X,Y) = ( 0, 0) mm
    • BPM4E (X,Y) = ( 0.6, 0.4) mm
    • See white board for updates on these.
    • Tolerances on these : +/- 0.3 mm
  2. Establish Raster
    • It gets turned off for access, (sometimes people forget.)
    • Still at empty target.
    • All scint HV off (normally they are).
    • Need to use T8 pulser, so use ps8 = 2 on L-HRS.
    • spot_L check of raster see 4.4 (width) x 7.2 (height) mm2
  3. Put in Carbon Hole (90 deg) target
    • 1 uA rastered beam on Carbon Hole target.
    • Lock the beam position using 1 uA current
    • Go to 20 nA current, turned on scintillators HVs and check spot++ on Carbon hole target.
  4. Put in the Lead /1% carbon target
    • See white board for which one we are using
    • IMPORTANT: Raster always on and 4.4x7.2 when Lead / Diamond target in beam !!
    • Ask for the SAME attenuator and slit as above.
    • Observe T1/T2 = 13 +/- 3 kHz. This is fine.
  5. Run spot_L again, this time with ps8=0 and ps1/2=10
    • Observe the raster current pattern, see if it's flat
    • Flat means we're not hitting a frame !
    • Increase raster by 50% and check spot++ again to make sure not hitting the frame
  6. Turn off all scint HV.
  7. Ready for high current: Ramp up to 50 uA at about 10 uA per min.

Procedure for Short Beam Down or target movement

less than 2 hours of no beam, and no changes to beam

IMPORTANT: Raster always on and 4.4x7.2 mm (observed on target) when Lead / 1% carbon target in beam !!

  1. If you are unsure of raster status, check it !!
  2. Can be sure raster is ok if
    • You were just running and it was on.
    • Check the scope in middle room (familiar TV pattern of raster)
    • Look at raster EPICS screen.
  3. To check raster:
    • Go to empty target
    • Ask for 1 uA
    • Do a spot_L run with ps8=2 as explained above.
  4. Put in Pb/1% Carbon Target
    • See white board for which one.
  5. Ask for 1 uA. Check beam positions.
    • BPM4A (X,Y) = ( 0, 0) mm
    • BPM4E (X,Y) = ( 0.4, 0.6) mm
    • See white board for updates on these.
    • Tolerances on these : +/- 0.3 mm
  6. If you didn't do spot_L in the first step, do one a quick one now.
    • Want 6x4 mm on target.
  7. Ready for high current: Ramp up to 50 uA at about 10 uA per min.