Beam Recovery

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PREX Main<< HOW TOs << Expert Tools


Establishing High Current on a Calcium Target



  • 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.)

Image 1 - 1H quad settings
Image 2
  1. Check if the 1H quads have changed - correct values are in halog 3708676
  2. See this log entry for more information on which quads to check before moving forward: halog 3779853
  3. Empty target, establish correct beam position Check beam position
    • BPM4A (X,Y) = ( 0, 0) mm
    • BPM4E (X,Y) = ( 0.6, 0.4) mm
    • See white board for updates on these.
  4. Establish Raster (12 width and 7.2 height in MCC units)
    • It gets turned off for access, (sometimes people forget)
    • Still at empty target.
    • All scint HV off (normally they are).
  5. 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
    • Keep an eye 1H04B, D to watch for changes during the low current running
    • Turn on scintillator HVs (S0A,B and S3 in each arm) - check T1 rates (~50-100 kHz) and reduce beam current if necessary
    • record attenuator and slit value
    • Check spot++ on Carbon hole target (see halog 3707033???)
      • Is the hole within 1mm of center of the raster in the horizontal direction?
      • Is the size of the raster about 4x6 mm2 (2mm diameter hole) in the plot?
  6. Turn off all scint HV.
  7. Put in the Lead target
    • See white board for which one we are using
    • IMPORTANT: Raster always on and 12x7.2 mm2 (MCC unit) when Lead target in beam !!
  8. Ready for high current: Ramp up to desired current 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 12x7.2 mm2 (MCC unit) 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) = ( 0.6, 0.4) 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.
    • Increase raster by 50% and check spot++ again to make sure not hitting the frame
    • Go back to 12x7.2 mm2 (MCC unit) raster size.
  7. Ready for high current: Ramp up to 50 uA at about 10 uA per min.