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PREX Main<< Information for Shift Takers << Shift Leader << HOW TOs


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 and high current, spot gives a (misleading but consistent) view of the rastered spot size using the BPMs

The steps involved in doing this measurement are:

  1. Take the spot++ run
  2. Analyze the run
  3. Make the plots and post to the logbook

How To Take a High Current spot++ run

  1. the high current spot run can be taken at any current above 1 uA or so. (Below this, the bpms won't work). This does not interfere with parity production
  2. Set the trigger prescale for PS8 =1, and all other triggers =0.
  3. Start the counting DAQs while beam is on.
  4. End the run after 50k events are collected. run spot++
  5. If you log the results (and you should) make a follow up entry to label this run as a "high-current spot" run.
  6. If you were trying to verify the raster size, search the logbook for previous "high-current spot" runs and compare the bpm raster plots. They should be approximately similar. If they match, you are good to go!

How To Take a Low Current spot++ run

Detailed instructions from halog 3711297
To center the beam on the Carbon hole center [1]

  1. Stop Parity DAQ, turn off beam modulation and Aq feedback.
  2. Prepare to use low current beam position monitors (4A/4E lock won't work with low current)
    • 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
      1. Ask MCC to turn off "slow lock" (=4A/4E lock), and enable "cavity lock" on 4B/4D
      2. Give them the values found above to be used as setpoints. Note that MCC operators are sometimes unfamiliar with how to establish "cavity lock". (This must be enabled on a special screen called Generic PID Lock)
      3. Verify that the 4A/4E position readbacks have not changed significantly from where they were before (check white board for current values, x/y 0.2/-0.5 and 0.2/-0.5 as of 7-31).
      4. 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
  3. Ask MCC to send ~20nA beam
    • You will have to give them the attenuator and slit settings (look in halog for settings used in last spot and start there)
    • The 4A/4E BPM signals will disappear
    • Hall current will read 0.00
    • Monitor the 4B/4D positions (they will fluctuate more as relative noise levels are higher)
  4. Set up the detectors for taking the spot data
    • Turn S3 and/or S0 scintillator HVs on for both arms. These are connected to channels L0.2 (S0 tab) in the HRS HV control panels.
    • Turn on other scintillator paddles and/or VDCs if requested
    • Observe the S3 and/or S0 trigger rates in the scaler GUI. Aim for less than 100 kHz.
    • If S3 and/or S0 rates are too high, ask for a lower attenuator setting (usually 1 tick is ~50kHz - go slow)
  5. While the shift leader was performing the above, the target operator should prepare the HRS DAQ
    • Take a test run to make sure things are working while the beam is being set up
    • Take at least 50k events for a quick spot, but for a target uniformity spot ~1M is better
    • End CODA runs
  6. Back out of the spot run
    • Turn S3 and S0 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 positions on the white board (x/y = 0.2/-0.5 and 0.2/-0.5 currently)
    • Log the history of 4A, 4B, 4D and 4E BPM positions during the entire above procedure.
  7. Unless otherwise instructed, go back to production running
    • 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.
    • Start a parity run

How to analyse the run

  1. Log into the a-onl account
    • ssh –X a-onl@aonl2# 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
  2. Plots should pop up after a few seconds
    • The most important plot is on the first page, titled "beam on target y vs x", see, for example RHRS run 21079
  3. When prompted, type y to upload the plots to the halog or n to skip this step

More Info

More information

Making plots for 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 as above.


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 or 0>,run#) (1 for LHRS, 0 for RHRS)
      • This version of the function creates a single plot of the map of the raster at the target. This plot as well as the rest of the macro uses the Raster2.rawcur
      • If this is done on the carbon hole target, you should see the hole on the plot. Make a rough visual estimate of what the bounds of the hole are on both the left and y axis
    • raster_check(<1 or 0>,run #,xmin,xmax,ymin,ymax) (1 for LHRS, 0 for RHRS)
      • xmin, xmax, ymin, ymax are the bounds on the carbon hole target from the 2D plot above
      • This function creates two plots, profile plots of the 2D raster map. Each plot has three different fiducial cuts applied in order to estimate the hole position better.
      • By zooming in on the x-axis of each plot and using the Event Statusbar, estimate the point on the x-axis of each plot where all three histograms overlap each other, on both sides of the hole.
      • To estimate raster size from the profile plots calculate 2*(max bin - min bin)/(max histogram overlap point - min histogram overlap point). Do this independently for both x and y.
    • raster_check(<1 or 0>,run#,0,100e3,0,100e3) (1 for LHRS, 0 for RHRS)
      • This function creates the profile plots like above but applies no fiducial cut to the histograms. This is best when looking at spot runs on the production target.
  • Post these plots to the halog if desired

More information about spot++

  • Hint: Type "spot help" to learn more options for spot++
  • spot++ output files go to:
  • For experts - macros, source codes, DB files are at:
  • You can get "strange printouts" of errors if you only type spot++ and the last run was for R-HRS because spot++ is aliased to spot_L

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

  • The cavities are used in <0.5 uA running territory (for commissioning a lead target with spot ++ check)
  • The cavity calibration is not quite reliable. Positions are best found by running at 1uA to set the position using the stripline bpms 1H04A and 1H04E, and then record the corresponding cavity positions.
  • Bob's EPICs variable printing to terminal script:
ssh apar@adaq