Special meeting on planning for a stable TAC run 4/6/2018

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  • Time: 11:30 EDT
  • JLab meeting room: ???
  • Connecting: detailed instructions are here
  • Conference id: 536076821
  • Present:


  1. Ideas for stabilizing the beam position without the beam profiler or active collimator
  2. Ideas for shielding the active collimator or otherwise reducing its sensitivity to synchrontron light
  3. What needs to be done to test or rule out some or all of the above ideas
  4. Understanding the source and spectrum of synchrotron radiation, as a step towards an effective shielding plan
  5. Prospects for nA-scale low-current TAC run with nA BPM's before May
  6. Other suggestions

Notes from this meeting, by RTJ

The following action items were agreed upon during this meeting.

  1. We think the cause of the excess rate far from the axis in the Active Collimator when running with the V-wire radiator is the same as the cause of the large X-ray backgrounds seen in the inner layers of the CDC when running without a radiator: synchrotron radiation coming down the photon beamline.
    • We want to test this hypothesis by measuring the absorption length of the radiation. We will do this by placing absorber foils of various materials and thicknesses in the beamline upstream of the active collimator, and measure their relative reductions of current in the AC wedges.
    • The best way to do this will be to attach them to the downstream side of the profiler, so they can be inserted into the beam and removed for a relative measurement.
    • The JLab group will come up with a short list of foils thicknesses and materials to use for this test.