Photon Beam Polarimetry

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This page contains a list of to do items for installing the triplet polarimeter for the Spring 2015 GlueX run. Items that used to be on this page are now at the bottom in Items From Before January 2015

Expected Timeline

  • February 2 - 5: Kei visits ASU (DONE)
  • mid-February: ship triplet to JLab (DONE)
  • End of February - mid-MarchApril: testing in EEL 126 (ONGOING)
  • After initial testing: Survey by JLab
    • April 3 - May 4: physics beam, installation when possible


Hardware Progress

Slides are mostly what Kei shows at weekly ASU group meetings

Vacuum outgas test results (fits in red dashed lines are with linear functions)

Hardware Division

  • ASU
    • motor (data sheet)
    • controller
    • power supply
      1. 4 channels of +12V, 0.21 amps per channel
      2. 4 channels of -12V, 0.21 amps per channel
      3. 1 channel of +200V, the leakage current on the silicon strip detecter is 3.3 micro-amps
    • 32 short SSI cables with Lemo
    • vacuum rated limit switches (data sheet)
  • JLab
    • fADCs
      1. 2 fADC250s on PSC VXS crate
    • 32 coax cables with Lemos on both ends (Fernando). Require 55ft to racks
    • turbo vacuum pump (Tim)
  • Test setup in EEL 126
    • Fernando has spare fADCs, cables (not fire rated)
    • Kei will look for adequate sources
    • Tim can provide vacuum (would like ~30 mTorr)

Things to do at ASU

  • packaging, shipping
  • testing(?)

Things to do at JLab

  • preparation of hardware before shipment
  • installation
  • Monitoring
    • Would like to run the device below 50 mTorr to avoid voltage breakdown. Need pressure sensor, monitoring (Note: this is being extremely cautious. We will be running at ~200V, and even with 300V the required pressure is, given d = 1mm, <6Torr)
    • Humidity: no requirements
    • Temperature: would like to monitor temperature in collimator cave since we don't want the preamps to get too hot. Need temperature sensor, monitoring
  • testing with source(?) - will we test with source before installing in beam line?


  • write proposal, safety concerns/procedures
  • Beryllium use:
    • will be used as radiator foil, 25μm thick
  • Get approval from Bert
  • Pass by Patritzia

Noise Levels

Slides are from Mike's presentation at ASU group meeting on February 11 2015.

  • Expected noise levels are shown below (click to expand)
    • Modulation of baseline is due to our old HV supply, this should improve once we get JLab supply
    • Spikes are due to LV supply (not sure why, but spikes are seen on LIMO line)
    • There is also a switching noise that may be present at the ASU setup lab only
    • Signal from α source is large (~>500 mV), β source signal will only be several mV
Noise1.png Noise2.png Noise3.png
Very low HV Medium HV High HV, signal shape

Analysis Procedures

  • beam requirements
  • requirements on other systems (PS, tagger)
  • analysis procedure
    • Think of procedure for high-level analysis to ensure data is good
  • online monitoring
    • fADC scalers for monitoring each sector → Hovanes
    • RootSpy plugin
  • MC - GEANT4 simulation available with previous geometry

Items From Before January 2015