Beam Checkout Procedures

Basic Beamline, Raster, Instrumentation checkout

Initial Raster checks

  Goals 
   - Establish beam to be roughly centered in beam pipe by locating it on YAG viewer just upstream of target.
   - Turn on Raster and verify beam profile expands as expected.
   

 - Beam Current:   Viewer limited (Tune Beam)
 - Target:         Empty, or solid target 
 - Raster:         Off; 2mm x 2mm

 Procedure
 - Insert YAG viewer on Hall C superharp girder
   - start with raster off, verify beam spot roughly centered
   - if the beam energy has changed, check that on the Hall C Raster Control GUI it is initialized for the correct beam energy (at the top of the GUI).
   - request raster on:  2mm x 2mm
     - watch beam spot on viewer and verify Raster's basic functionality
 - Retract viewer

Harp scans

  Goals 
   -Verify operation of Harp scanners w/ beam.
   - Establish acceptable beam profile (nominal 100--500um sigma)

 - Beam Current:   5 uA Tune Beam
 - Target:         Empty, or solid target 
 - Raster:         Off

 Procedure
   - Verify that the raster is OFF for the harp scans at the target (3H07) 
   - Ask for harp scans with IHA3H07A and IHA3H07B
   - verify beam profile (nominal 100--500um sigma) on at least one scanner on Hall C upstream beamline (good to check 3H07A/B)

Target/Beam centering, Raster calibration

  Goals 
   - Establish beam position on target.

 - Beam Current:   5--10 uA CW
 - Target:         BeO, Carbon Hole

 Procedure
 - Note:  DAQs should be running and a solid target is in place
   - Online shift crew will proceed with program below.
 - We need to have a reasonably high (~1 kHz) trigger rate in at least *one* of the two spectrometers.
   It may be helpful to (temporarily) lower the spectrometer momentum setting and/or move the arm to a more forward angle.

 - Attempt to view beam on BeO (if available in target ladder)  ** NOT available in current target configuration (2017--2019) **
     - Target:    BeO
     - Current:   5 uA CW
     - Raster:    OFF
   - Target camera: ON
   - Target lamp:   OFF
   - Log camera snapshot of beam spot on BeO

 - Image Carbon Hole target using Raster current pickoffs vs. raw trigger rates in SHMS and/or HMS
     - NOTE: If there are issues with the raster systems, this step can be skipped provided experts are confident that we know where the beam is on target
     - Target:    Carbon Hole
     - Current:   5+ uA CW  (Whatever is needed to achieve a reasonable 3/4 trigger rate in at least one arm.)
     - Raster:    3mm x 3mm (Something significantly larger than the diameter of the hole in the Carbon foil.)
   - Run DAQ on SHMS / HMS / COIN
     -   Set prescales to ensure DAQ rate is dominated by scintillator triggers (ie. 3/4)    
     -   For the COIN DAQ, set the target rate for PS1 and PS3 to be 1000Hz, save the prescale values before starting a run
   - Run the online analyzer (HMS/SHMS 50k scripts) and look at the 'Fast Raster' panel of the online GUI:
     - For PionLT 2021, execute ./run_coin_hms.sh or ./run_coin_shms.sh, see here for more information
     - Locate the hole in the 2D intensity histogram.        
        - NOTE: if the beam energy in standard.kinematics is not up to date, the distance scale on the 2D histogram will be wrong

   - Center Beam on using Carbon-Hole Target:
     - Iterate until the hole is clear, and is centered in the square raster pattern
       - Adjust beam position
       - Re-run the online analzyer on the new file(s) to see the effect of a raster size change and/or beam position change.  Make sure changes are logged in the CODA start-run entries!
   - Calibrate raster dimensions against (known, typically 2mm diam.) Carbon Hole diameter by adjusting Raster magnet settings until raster an appropriate size (RC will know).