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
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 - Set prescales to ensure DAQ rate is dominated by scintillator triggers (ie. 3/4) - Run the online analyzer and look at the 'Fast Raster' panel of the online GUI: - 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).