[Bteam] Notes from Monday's Compton Tune meeting

Mon Nov 9 19:50:16 EST 2009

Below are my notes from today's meeting on obtaining a clean compton 
tune.  We will pick this discussion up and finalize the plan after the 
8am meeting.  Thanks for attending and I'll see everyone tomorrow morning.

  Arne's Journal

    1 Hall-A Compton Meeting OPS SELECT Bteam AHLA

2009-11-09 Mon 14:24

      1.1 Injector Summary Reza

Roughly same setup as for Happex-III. This setup results in a large 
compton rate.

    * pre-buncher is at 0.95
    * capture phase
    * laser phase
    * small adjustment of lens in front of the 1/4 cryo unit.
    * BLM in chicane trip as current approaches 200 ? A
    * The 1kHz/? A rate drops at high current due to pile up.

      1.2 Hall-A transport Yan

    * Dog4 was railed and has been fixed today.
    * small dispersion in Arc8 and Arc9.
    * Orbits look reasonable in the machine.
    * Horizontal orbit in A line is not nominal. Horizontal position at
      target is -2.4mm.
    * Upstream of compton chicane appear to the same as for Happex-III
    * Steering up/down left/right shows no changes.
    * BLM activity is low
    * Compton ion chamber shows some counts with high current, normally
      the ion chamber reads zero at all currents.

      1.3 Matching summary Michele

    * ? and TWISS measurements on Thursday were successful and showed
      that the horizontal match was the most problematic.
    * Match was loaded
    * Beam size measurements after match was loaded on Friday, showed
      that the beam was no longer matched.
    * ? and TWISS measurements on Monday show that the horizontal ? and
      ? values have changed.
    * Using the Monday input measurements, the predicted size for the
      beam agrees with the Friday harp measurements, so it appears that
      the machine has been stable since Friday.
    * What is the dispersion leakage in the matching region?
      .05/.8=?_1C05 /?_1c12 if ?_1C12 = 4m, then ?_1C05 = 25cm. Is this
      significant?

        1.3.1 Post meeting information

Addition match data was taken after the meeting. Again horizontal plane 
shows some changes, whereas the vertical plane is reasonable constant. 
Some of the differences between the data set is the excitation of the 
Hall-A dipole string. Is this causing a fringe field upstream of 1C05?

      1.4 Raytrace summary Tief

    * No significant distortion in horizontal and vertical.
    * But some distortion is introduced in the compton region.
    * emittance reasonably conserved.

      1.5 Suggestions

    * Requirements from Hall-A are that the photon count rate should be
      below 100 cnt/? A.
    * Can OPS have access to the "real" rate so that we can see how
      close the rate is to the maximum rate at which the photon counter
      saturates? Alex says yes, see action item.
    * Waveform and FFT of the compton counts to see if the MOMOD
      frequencies show us anything.
    * SEE BPM FFT could be used as well to look for a source or loss of
      specific frequencies.
    * Change injector optics back to M_56 ? 0 for different bunch
      compression.
    * Look at orbits for 5.9GeV run in March 2010.
    * null out dispersion leakage
    * Is the 5-pass separator operating at the right point.

        1.5.1 Post meeting suggestions (Tiefenback)

    * Mike Spata had expressed concern over the separator high power.
      Whether this could be a source of problems can be tested by
      turning the separator off and using magnetic extraction (even if
      only for 20 minutes) to check for HallA Compton background count
      sensitivity.
    * It is possible that there is some injector-sourced bleed-through
      causing a diffuse background beam in the Hall A line. Shutting the
      B and C slits (even for 10-20 minutes) might be a worthwhile test
      of whether there is any contribution from this source. (I suspect
      not, but I'm all for ruling things out cleanly.) With the beam
      quality questions we have, it may behoove us to close down the
      Hall A slit partially to restrict the longitudinal acceptance of
      the injector and improve the quality of the beam at 10 uA-ish
      current levels (turning the pre-buncher down or off). This would
      rule out injector-sourced halo (along with closing the B and C
      slits) as a contributor to the HallA Compton background.
    * With the HallA slit narrowed down, a laser phase scan across the
      slit would help us confidently to conclude that the injector is
      not fogging the beam line.
    * Reza had suggested that the Wien filter does not now have the same
      setting it had at 5.9 GeV. This is not a high-confidence problem
      source for the Compton background, but it is too simple to do and
      the Wien has been subject to too much ugliness in the past not to
      look. I'd endorse changing the Wien filter back to the 5.9 GeV run
      settings just as a test, not as a long-term configuration. The
      more things we can rule out and the better we understand the
      parametric behavior, the better able we will be to identify and
      correct this nagging issue.

      1.6 Actions

        1.6.1 TODO Communicate EPICS record name of the raw photon rate Alex

The epics record name of all Compton epics records with human readable 
description should be communicated to OPS (Arne).

        1.6.2 TODO Provide independent of compton equipment halo
        detector Alex

Either pick an existing detector that is tightly correlated to Compton 
detector that is robust and always on. Put it in EPICS and tell OPS 
about it. This detector should be stay on all the time and have stable 
configuration.

        1.6.3 TODO Escort Mike Tiefenback on a tour in Hall-A Alex

      1.7 Thursday

   1. Check main machine, check/fix A orbit.
   2. Restore beam to A
   3. Check compton rates
   4. Load new Match quads
   5. Check compton rates
   6. Measure beam size will ALL accelerator harps in the A line.
   7. Go straight ahead mode (not through compton) and measure compton
      background.

      1.8 Friday

   1. Null vertical spin component (Grames)
   2. Make A-B-C beams co-linear
   3. Look for obstruction in Injector
   4. Measure Compton
   5. Steering in 0L region vs. compton count rate.
   6. check 5 MeV dipole chamber
   7. ???
   8. ????
   9. ?????
  10. ??????
  11. ???????

Author: Arne Freyberger <freyberg at jlab.org> <mailto:freyberg at jlab.org>

Date: 2009-11-09 19:47:38 EST

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