Beam and Raster Checkout for A1n/d2n (Short Procedure)

When should we do a short beam checkout?

• After beam studies (typically on Tuesdays)
• If for some reason the accelerator has been down for a "significant" period of time (say, more than ~8 hours)
• If anything "significant" has changed in the beam line and you are not sure if it will affect the position or profile of the beam delivered to the hall

Procedure

Beam restoration stripcharts

Target motion control

Open Stripcharts

• You should monitor the beam position, mode, and current during this process.
• Open a terminal and run go_beam_recovery_stripcharts. You should see something like the image to the right.

• The first set of 4 charts are the field integrals of the orbit lock corrector magnets.
  • If they are operating properly, you should see the value changing when the beam is on. This means they are properly keeping the beam in the position we want.
  • These will flatline when the beam trips. This is normal behavior.

• The second set of charts are beam positions at harps 3H07A and 3H07C. These positions (set by the corrector magnets) should match the nominal values on the wall screen.

• The third set of charts are BCM current and Hall C beam mode, which indicates what type of beam MCC is sending. You should monitor both.
  • Mode 2 is tune beam (beam with a 1.5% duty factor used when first checking the orbit and sending beam to the hall).
  • Mode 3 is CW

• The last plot is the target ladder position in volts.
  • This readout matches the voltages displayed on the target motion control GUI.
  • The two values shown here, 7.88V and 7.11V, correspond to Pickup Coil and Pol He3 Cell respectively.

Harp scans

Purpose

• Verify operation of Harp scanners w/ beam.
• Establish acceptable beam profile.

Note

• We need sigma=100–500um at the target
• If sigma is larger than 500um, ask MCC to tune beam.
• Once sigma reaches below 500um, call RC for advice on whether we should accept the beam.

Setup

• Beam Current: 5 uA CW
• Target: No Target
• Raster: Off

Procedure

Harp scans

1. Verify that the raster is OFF
2. Ask MCC for harp scans with IHA3H07A and IHA3H07B
3. Verify beam profile:
   1. Find the harp scans on the Ops ELOG. They should be titled "HarpFitter: IHA3H07A" and "HarpFitter: IHA3H07B"
   2. Open a terminal and run `harp_project_to_target`
   3. Enter the sigma values from peak 2 and peak 3 of both harp scans
   4. The script will project the width to the target and suggest an appropriate raster diameter to request from MCC
   5. Confirm with the RC that this value makes sense.

• If you'd like to verify the projection script's arithmetic, you can use the distances in Dave Gaskell's comment on this log entry.
  • https://logbooks.jlab.org/entry/3764458
• The script's repository has a longer discussion of projecting the width from the harps to the target.
  • https://github.com/johnmatter/harp_scan_projection

Raster check with YAG Viewer

Purpose

• 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.
• No CW beam should be allowed in the Hall until this step is completed.

Setup

• Beam Current: Tune Beam (Viewer limited)
• Target: No Target
• Raster: Off; 5mm diameter

Procedure

1. Call MCC to insert YAG viewer on Hall C superharp girder.
2. Start with raster off. MCC should post a picture. Verify the beam spot is roughly centered.
3. If the beam energy has changed, check that on the Hall C Raster Control GUI it is initialized for the correct beam energy.
4. Request raster on with the diameter determined from the harp scans.
5. Ask MCC to post a video of the viewer. It should show beam spot on viewer expanding larger than raster off case, and the beam spot size should show a breathing pattern.
6. MCC will retract viewer after check is done.

• An example of what to look for can be found in https://logbooks.jlab.org/entry/3764451
• Another example posted in elog: https://logbooks.jlab.org/entry/3768480
• Here is an example of how to interpret the images on the YAG viewer: https://logbooks.jlab.org/entry/3749551 (taken during initial beam checkout in December 2019).

Check Beam Positions And Locks

Purpose

• Ensure that the beam positions are what we expect.
• Do this if nominal beam positions are already established.

Setup

• Beam Current: 5 uA CW
• Target: No Target

Procedure

As of January 26th, 2020, the positions should look like the orbit lock image on the right (from this log entry).

1. With "No Target" position, ask MCC for 5uA CW and verify beam position with established nominal position
2. Verify the orbit and current ramp locks are enabled. If you don't know where to find this information, consult the steps below.

Orbit Lock

Orbit lock

1. Search for "orbit" in jmenu, and select "Orbit Locks Expanded View" from the drop down menu
2. Find the row labeled "HallCOrb" (this box should be green!)
3. Click the far right button labeled "Other", and select "HallCOrb Corrector and Bpm Info" from the drop down menu
4. Verify that the values in the light blue boxes match the nominal positions.

Current Ramp Lock

Current ramp lock

1. Search for "current ramp" in jmenu, and select "Hall C Ramping" from the drop down menu
2. Verify that the box next to "Crew Chief Enable" is green and says "Enabled"

Target/Beam centering, Raster checkout (optional)

Purpose

• Establish beam position on target, check/confirm raster size
• This step is optional, consult RC whether we need to do this.

Procedure

• https://hallcweb.jlab.org/wiki/index.php/Beam_and_Raster_Checkout_for_A1n/d2n_(Long_Procedure)#Target.2FBeam_centering.2C_Raster_checkout