Beam Centering

Back to Installation and Commissioning

Beam Centering procedure WITH spot++

1. Move target to None Target
2. request 5uA beam with 2x2 raster
   1. note scaler rates for s0, GC sum, & shower sum
   2. Scaler rates with cosmic LHRS scalers RHRS scalers
3. Move target to Carbon Hole
4. request 5uA beam with 2x2 raster
5. Run CODA to take data, run spot++, look for hole on 2d plot
6. Compare spot ++ with examples
   1. spot ++ Example 1
   2. spot ++ Example 2
      • If: the square of the beam spot is visible, but the hole is not
        1. move the beam 2mm in any direction and return to step 4
      • Else If: the hole is visible in the square beam spot
        1. center the hole in the square by moving the beam
      • Else If: the beam spot doesn't look right
        1. Tell the Run Coordinator!
        2. Proceed to "Coarse Beam Centering WITHOUT spot++"
   3. Proceed to "Raster Target Check"
   4. When beam is centered, scaler rates should be similar to those in step 2b (cosmic rates)

   Coarse Beam Centering procedure WITHOUT spot++:

   CALL RC BEFORE EXECUTING THIS PROCEDURE. YOU SHOULD NORMALLY USE SPOT++ INSTEAD

   1. Move target to None Target
   2. Request pulsed, unrastered beam
      1. note scaler rates
   3. Move target to Carbon Single Foil
      1. note scaler rates (make sure rates are noticeably higher than Step 2a!)
   4. Move target to Carbon Hole
   5. Request delivery of pulsed, unrastered beam
      1. note scaler rates
      • If 4a ~ 2a:
        1. Congratulations! The beam center is within 2mm of target center!
        2. Proceed to "Fine Beam Centering WITHOUT spot++"
      • Else If 4a > 2a:
        1. The beam is hitting the carbon
        2. Scan the beam in +x direction until the beam hits the target support structure (scaler rates will get much larger).
        3. note beam position (x,y)
   6. move beam +/- 1mm in y, note scaler rates for each
   7. scan the beam in -x direction until the beam hits the target support structure
      1. note beam position (x,y)
   8. If Step 6 +y > -y:
      1. change beam x position to average of Step 5c x-position and Step 7a x-position
      2. scan beam in +y direction until the beam hits the target support structure
      3. note beam position (x,y)
   9. use 5c(x,y), 7a(x,y), and 8c(x,y) to calculate the center of the circular carbon target
   10. Proceed to "Fine Beam Centering WITHOUT spot++"

   
   

   Fine Beam Centering WITHOUT spot++:

   CALL RC BEFORE EXECUTING THIS PROCEDURE. YOU SHOULD NORMALLY USE SPOT++ INSTEAD

   1. Request 5uA unrastered beam
   2. Find three points on the edge of the carbon hole, with a similar technique as in "Coarse Beam Centering"
   3. Calculate center of carbon hole using the three edge points.
   4. Move beam to calculated center position
   5. Proceed to "Raster Target Check"

   
   

   Raster Target Check:

   1. Move to Raster Target
   2. Request 5uA, unrastered beam, note scaler rates
   3. Request 5uA, 2x2 rastered beam, note scaler rates
   4. If the rates are similar, proceed with data taking
   5. If the rastered rate is higher, repeat beam-centering procedure