Measuring   the   Rastered   Beam   Spot   Size   on   Target

Robert Michaels, rom@jlab.org, Jefferson Lab Hall A, July 2006

This file:     hallaweb.jlab.org/equipment/daq/spot.html

• PURPOSE:   To display the rastered beam spot on target in Hall A.

Additional diagnostic BPM histograms and tree variables are generated in root file ~adaq/rastersize/ARM_DIR/rastersize.root   where ARM_DIR = LeftHRS or RightHRS.

• SIMPLEST USAGE:     Start a CODA run on L-arm (R-arm) DAQ and type "spot_L"   ("spot_R")   Note, the old notation "spot++" or "raster" or "raster++" are all synonymous with spot_L at the moment. When running DAQ in coincidence mode, either spot should work. Run spot on adaql1 (Linux) on adaq account.     Note: The beam must be on ( > 1 uA) for some time in the first 5000 events !!

• MORE DETAILS ON USAGE:

  • Type "spot_L" or "spot_R" with no arguments   --> to analyze the most recent run.
  • Type "spot_L 1062"   --> to analyze run 1062 (if it's still on adaq disks).
  • Type "spot help"   --> to get help (note, there are other command line options, which "help" will explain).

•  COMMON SENSE TIPS :
A few common sense tips about raster and spot size:   Do not confuse the "rastered spot size" (of order 4 mm) with the "intrinsic spot size" (typically 10 to 100 times smaller).   If your purpose is to check the spot size and dwell time to avoid destroying the target, then test at low current, say 1 microamp, before going to high current on target. Or test with no target in the beam.   A good double check is the oscilloscope trace of the raster current, seen in the middle room (electronic rack room) of the counting house.