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Spring 2016 Compton

The Compton polarimeter is used to (non-invasively) monitor polarization of the incoming electron beam. It has three major components: an optics table with a laser that can lock to a Fabry-Perot cavity, an electron detector, and a photon detector to count scattered electrons and photons, respectively.

Last edit: LThorne 02:08, 24 February 2016 (UTC)

Shift Workers' Operation Guide

Start a Compton run every two hours.

The Compton DAQ is located in the back room in the Counting House. All commands are done from compton@compton.

If CODA is not already running:

Kill CODA first, then start it up again:
   $ kcoda
   $ startcoda
A few new Terminal windows and a GUI pop up.
LT CODAgui.png
Let "top" refer to the bar with named menu options near the top of the GUI (ex: Platform, Sessions, etc). Let "bottom" refer to the bar below "top" that contains a line of buttons (hover over them to reveal their labels; starting with "Configuration" on the left).
  1. In top, select: Platform > Connect
  2. In bottom, click on "Configuration" button.
    • If configuration listed in the "Run Parameters" box is not FADC_prod: in top, select Configurations > Cool and change it to FADC_Prod.
  3. In bottom, click on "Download" button
  4. In bottom, click on "Prestart" button
  5. When ready to start run, click "Start" button. Typical run duration: 2 hours. Type in any Start Of Run comments in the box. Click "OK" (even if you left comments blank!).
  6. When ready to stop run, click "End" button. Type in any End Of Run comments in the box. Click "OK" (even if you left comments blank!).

Compton Experts' Operation Guide


  1. HV on/off? -> Compton#High Voltage Controls
  2. [Experts only]: Correct parameters for run in integratingDAQ.flags and compton.params

Run Compton analysis:

In compton@compton:

   $ cd /home/compton/online/CompMon

Run analysis software:

   $ ./compmon <run number, no brackets>

Open ROOT:

   $ root -l /data/cmuwork/rootfiles/Fall2016/compmon_<run number, no brackets>.root

Run desired C script located in CompMon directory.

Some useful analysis scripts:

  • /home/compton/lthorne/CompMon/plotAsymSpectrum.C: Quick and dirty view of asymmetry histograms, cavity and BCM limits.
  • /home/compton/lthorne/CompMon/buildQuartets.C and buildQuartetsPlot.C: For constructing multi-run asymmetry plots.
    • Run instructions are given in the comments at the beginning fo the file.
  • /home/compton/lthorne/CompMon/BCMCal/calibration<runNumber>,C: BCM calibration scripts for specific runs.
  • /home/compton/lthorne/CompMon/plotAccQuartets.C: plots sum, difference histograms for beam off, laser on, laser off for Acc0, Acc4.
  • /home/compton/franklin/CompMon/plotPulser.C: peek at DAQ pulser channels, including info on 'variable' and 'delta' for channel 13.

Link to list of good Compton runs:

List of runs with comments, so know which ones were not junk.

Juan Carlos Google Docs: Runlist (Email Juan Carlos if you want to granted write permission)

Taking an LED run:

  1. Find parameter file GUI:
   $ cd /home/compton/franklin/
   $ ComptonConfig
  1. Click "Pulser On, Pulser Trigger" on parameter file. Click "Apply", then "Done" to close GUI.
  2. Go to CODA. Start a new run to apply the settings. (This does not need to be a long run. You may end it immediately.)
  3. Start your LED run.
  4. When you go back to normal Compton runs: don't forget to turn the pulser off and do a short run to update the parameter file settings!


Electronics, etc.

Special 5-pass instructions

(Update this section)

  1. Insert capacitor (presently stored just behind the Tungsten Collimator Control Box -- JAWS) control box. It's just a BNC terminator with a capacitor on the end: Compton5PassCapacitor.jpg
  2. Add extra lead sych shield #6 in front of photon detector table. Remember to update the wiki if this occurs. ComptonSynchShieldSetup.jpg
  3. Make changes to .flags file

Centering the Beam on the Laser

Open jaws all the way:

   aperture = 43.69 mm
   y center = -3.28 mm

Tell Dave to make the laser stop flipping. MCC may be looking at the Compton rates, so it's a good idea to let them know we are doing a centering procedure, and to ignore the fluctuation in rates for now. Let them know when the procedure is done.

Use the strip tool for this to watch Compton rates (ComptonCentralRate, ComptonCentralRateHigh) as you change the Y beam positioning. This position will change daily, so may need frequent adjustment.

The laser spot is 0.9 mm, so use small incremental steps. Suggested incremental step change: 0.5mm at a time. No need to map out everything; stop when you think you've located the laser beam.

Photon Detector Table

For controls, troubleshooting: Compton Photon Detector

Home position of photon detector table: (Dave insert, please)

Collimator Systems

  • Remote-controlled tungsten collimator system ("Jaws"):
    • EXPERTS ONLY jaw controls: [1]
    • Live Compton camera: [2]
  • Lead cylindrical collimator:
    • Length approx 10 cm with two openings: 1 and 2 cm diameters
  • Synchrotron shielding:
    • 7 individual thin shields that are numbered, with thickness denoted in X.XX mm +/- 0.01mm:
      • #1: 1.56
      • #2: 1.61
      • #3: 1.61
      • #4: 1.62
      • #5: 1.64 <--- currently in (inserted 2016-10-27)
      • #6: 1.64 <--- currently in (inserted 2017-11-10)
      • #7: 1.67

High Voltage Controls

Know the HV channel and navigate to the GUI: HV Control GUI

Laser System

Real time o-scope signals

Cavity lock camera

Make sure laser flipping is on

Turning off the laser

IOC reboot

Accessing the laser hutch in the hall

Laser and Locking troubleshooting

Software & Data Analysis

Relevant files, scripts, etc.

Helicity controls

From within NewTools controls (see first few steps in Compton Photon Detector Compton GUI section):

  1. On far right of JTabs menu, there are "master" controls. Find and click on Tools Screen.
  2. Go to the helicity controls. (The default is delayed, so be careful of this.)

Current Scripts

As a brief check, run plotAsymSpectrum.C.


Compton Meetings

See last list entry for most recent meeting.

Current Compton Experts

Expert Phone
Dave Gaskell x6092
Alexandre Camsonne x5064
Ciprian Gal x6235
Juan Carlos Cornejo (Photon Detector) x5282

Expert Information

For expert monitoring and troubleshooting information please visit Compton Expert Information.

Old Compton page (pre-Spring 2016)

See Pre-Spring 2016 Compton

Last edit on 2018 08 01, by Gaskelld