Spot++
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Description
Performing a spot++ allows us to "image" the target or raster size by plotting the hits as a function of raster x and y current
- CASE 1 If you run with T1 or T2 trigger and target in place, spot gives a view of the target density
- CASE 2 If you run with pulser trigger T8, spot gives a view of the rastered spot size
The steps involved in doing this measurement are:
- Take the spot++ run
- Analyze the run
- Make the plots and post to the logbook
How To Take a spot++ run
Detailed instructions from halog 3711297
- Stop Parity DAQ. Turn off parity beam modulation, Aq feedback.
- Prepare to use low current beam position monitors (where 4A/4E lock won't work)
- Ask MCC for 1uA current
- Record the x/y positions of BPMs IPM1H04B and IPM1H04D at this current (with target position lock on 4A/4E)
- Ask MCC to disable FFB
- Switch to locking on 4B/4D at the exact positions noted above
- Ask MCC to turn off "slow lock" (=4A/4E lock), and enable "cavity lock" on 4B/4D
- Give them the values found above to be used as setpoints. Note that MCC operators are sometimes unfamiliar with how to establish "cavity lock". It can be enabled on a special screen. Ask Caryn to communicate with MCC if necessary.
- Verify that the 4A/4E position readbacks have not changed significantly from where they were before (check white board for current values, -0.2, 1.3 as of 7-28).
- If they have moved, you can go ask MCC to undo the cavity lock and to put them to the desired locations and reset the lock
- Ask for injector attenuator to be set to ~103.
- This will lower the beam current below 1 uA.
- The 4A/4E BPM signals will disappear. Hall current will read 0.00. 4B/4D positions will fluctuate more as relative noise levels are higher now.
- Set up the detectors for taking the spot data
- Turn S3 scintillator HVs on for both arms. These are connected to channels L0.2 (S0 tab) in the HRS HV control panels.
- Observe the S3 trigger rates in the scaler GUI. Aim for less than 100 kHz.
- If S3 rates are too high (we got 150 kHz with attenuator = 103), ask for a lower (sic) attenuator setting. We asked for attenuator = 101, resulting in S3 rates of 75 kHz.
- Take the run.
- Take 2M events. This may take around 30 minutes.
- End CODA runs. Run spotL/spotR analysis for all events. While spot is running, back out as follows:
- Turn S3 HVs off.
- Ask MCC to set attenuators back to nominal setting and deliver 1 uA of beam.
- At 1uA, ask MCC to turn off "cavity lock" and re-enable "slow lock" on BPMs 4A/4E using x/y = -0.2/1.3 setpoints for both.
- Log the history of 4A, 4B, 4D and 4E BPM positions during the entire above procedure.
- Go to 70 uA.
- Ask MCC to re-enable FFB. This may require gain searching.
- Once FFB is stable, re-enable beam modulation and Aq feedback.
Previous notes:
- If part of a Beam Recovery procedure, make sure you have taken a CODA run in counting mode for the LHRS
- Monitoring the beam positions
- At 20 nA the BPM plots look funny (= no signal)
- Scintillator HVs (S0A,B and S3 in each arm) need to be on
- Make sure the beam is off before you turn the HV on
- Check that the voltages are set properly
How to analyse the run
- Log into the a-onl account
- ssh –X aonl@aonl2 –l a-onl# Then type either:
- spot_L run# for the LHRS (Recommended)
spot_R run# for the RHRS
- If no run # is given, analyzes last run taken
- Plots should pop up after a few seconds
- When prompted, type y or n to upload the plots to the halog (or not)
- output file goes to:
/chafs1/work1/spot/
- (For experts) macros, source codes, DB files are at:
/adaqfs/home/a-onl/rastersize/
- You can get "strange printouts" of errors if you only type spot++ and the last run was for R-HRS, so it's clearer to do what is listed above than to use spot++. (note, this is because spot++ is actually spot_L).
- Hint: Type "spot help" to learn more options.
- In case 1 or 2 above, the most important plot is on the first page, titled "beam on target y vs x", for example:
https://logbooks.jlab.org/system/temporary/FADC_prex_21079.pdf# HRS CODA instructions
Making the plots
Long Runs
Most of the time we just want the normal length of spot++ run, which is 50k events. But occasionally we want to take a higher statistics run, and the spot default is to only analyse 50k events. However, a command like:
spot_L run# firstEvent lastEvent
will analyze the events in the specified range.
This will output the .pdf to the logbook in the same way.
Alternative Plotting
An additional way to make plots is to use the raster_check script.
- go to the /adaqfs/home/a-onl/rastersize/ directory
- open root
- .L raster_check.C
- raster_check(-1,run#) (-1 for LHRS, 0 for RHRS)
- raster_check(-1,run#,0,100e3,0,100e3) (-1 for LHRS, 0 for RHRS)
- Post these plots to the halog if desired
What do the plots mean?
Need to put examples of output when we have them
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
Cavity BCMs
- Low Current running Cavity BCM nominal points
- The cavities are used in <0.5 uA running territory (for commissioning a lead target with spot ++ check)
- Bob's EPICs variable printing to terminal script:
ssh apar@adaq ~/scripts/showCav.C
