SBS spot++ (beam size verification)

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Procedure to check beam position and/or calibrate raster size

NOTE: If this is the first time this is being done at a new beam energy, go to the complete instructions for establishing beam in the Hall

Raster plot.png

BigBite setting: Check run plan (nominal: current = 750 A, polarity = negative)
Super BigBite setting: Check run plan (nominal current = 2100 A, polarity = positive)

  1. If you are doing this for the first time at a new beam energy, turn off GEM HVs. Make sure BB shower and pre-shower HVs are on.
  2. Go to the carbon 2~mm hole target.
  3. Set the BBCal threshold at 175 mV to get the trigger rate reasonably large.
  4. Set pre-scales to BB only: set PS1=0, all others -1 (for more information see HOW TOs)
  5. Request the raster be set to 2x2mm in MCC units and verify that it is there. Iterate 5-11 as necessary with small adjustments to position and raster size to approximately get the hole position centered on the raster plot and approximately the same size as the raster square (see Fig. 1 for good example plot).
  6. Ask for 2 uA of beam (can go as high as 5 uA if you are reasonably centered and calibrated).
  7. Take data until at least 50k events have been reached for sufficient statistics
  8. Stop the CODA run
  9. Log into a-onl@aonl1.
  10. Run the command rasterCheck run-no [height] [width], where height and width are the raster sizes in MCC units. This will produce a plot of the raster Y vs X which should have the carbon hole centered in the 2D plot.
  11. When quitting the ROOT session that produced the plot in the previous step, the user will be prompted to post the plot to the HALOG. Enter y or n as requested. y will result in a new HALOG entry with the plot you see on your screen (e.g., on the right of this page).
  12. Mark down the raster size for the given beam energy in the beam parameters section of the Wiki.
  13. If required, set pre-scales back to those desired for the data-taking program.

Optional further analysis

  • To produce a set of plots of the raster and BPMs, run the command: spot_L run-no, where run-no is the CODA run number of the raster scan. After a few moments, the plots will pop up. When prompted, enter y on the command line to post the plots to the HALOG (n does not post to the HALOG).

Plot Descriptions

  • BPMA y vs x: Shows the beam location at BPM A
  • BPMA x: Shows the number of events at each x value in BPM A
  • BPMA y: Shows the number of events at each y value in BPM A
  • BPMB y vs x, BPMB x, BPMB y: Same as above but for BPM B
  • Beam at target y vs x, …x, …y: Same as above for at the target
  • BPMA Antenna 1, 2, 3, 4: Signal at the four wires of BPM A, one for X+, X-, Y+, Y-, respectively
  • BPMB Antenna 1, 2, 3, 4: Same as above but for BPM B


  • Raster Description [1]