Notes from Local Meeting - May 7, 2003

• Lumi (Riad)

  New Lumi detector installed at small angle. Second one is being assembled.
  No data has been taken yet with the new Raster (Triangular raster, rather than the circular raster used during Spin-Duality). Expect to take data soon. And should have enough data to verify the first design. If GDH ends at the end of the next week, there will not be enough time to test a second Lumi design.
  Cables to Spectrometer DAQ have not yet been terminated. May be done very soon. These cables will be somewhat shorter and better shielded than the old, temporary Lumi cables going to the counting house, and so may contribute less to pedestal noise (now about 20 ADC channels).
There was some discussion about the current state of the Septa. For more information, please see the Hall-A Meeting Minutes for May 6th (HTML).

• Cryo-Target (David)

  Hydrogen (Racetrack and Beercan cells) are ready to go and are on the cell block
  Some difficulty with soldering the Helium Racetrack cells to the cell block. If the problems cannot be resolved, an option is to use the 10cm "tuna can" style cells which are ready to go, and are on cell blocks. However cannot achieve the same luminosity.
  There was also some question as to whether the amount of Helium required to use a Helium Cell could be acquired at the same time as running the experiment with the Septa. The target group has suggested that the loss of luminosity from the use of the shorter target will be marginal, as the luminosity limit will come from limits on Helium cryogen flow, with combined needs from thick He target and septum limiting beam current. It isn't clear how reliable or precise these estimates of Helium usage are.

• Backgrounds (Kent)

  More realistic simulations including rescattering (possibly GEANT) should be done. It was generally agreed that this issue appears less urgent now that the current problems were seen to be related to septum malfunction and not background issues.

• Results From Recent Injector Beam Studies (Kent)

  Slides shown (PostScript). Main results:
  • Procedure is now outlined for setting Rotatable Half-wave plate and Pockel Cell Voltages for minimizing Charge Asymmetry and Position Differences.
  • Birefringence Gradient may be the dominating factor in Position Differences observed with Pippin (the "good" Pockels Cell). Steering effect and analyzing power gradients on the cathode were shown to have negligible contributions on position differences. Birefringence gradients appear to be much worse for Pippin than for Merry, while Merry has been measured on the laser table to be much worse than cells Brian had used at SLAC. More are being purchased.
  • Some Charge Asymmetry Effects have been observed to be caused by the beam clipping on aperatures in the Injector. Upstream of any known aperatures, a charge asymmetry effect of the PZT mirror points to significant QE gradient on the cathode.

• Measure of Birefringence Gradient in Merry (Brian)

  Slides shown. One source could be the amount of stress put on the cell by the mount. New cells ordered have "better" mounts and tighter specs on birefringence.