Spot++

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

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:

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

How To Take a spot++ run

2. If part of a Beam Recovery procedure, make sure you have taken a CODA run in counting mode for the LHRS
3. Monitoring the beam positions
   • At 20 nA the BPM plots look funny (= no signal)
4. 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

1. 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
2. Plots should pop up after a few seconds
3. 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/ 

1. analyze more than 50k events
2. how to plot the output in a useful format

• 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.

1. 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

More Info

Making the plots

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.

An additional way to make plots is to use the raster_check script.

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