BLTWG Meeting 1/31/2008

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  • Time: 10:00 EST
  • Place: EVO and ESNET
  • Present: R. Jones, G. Yang, F. Klein, T. Whitlatch, and E. Aschenauer


  1. Review of progress on subsystem specifications
  2. Answers to latest questions from engineering design firms
  3. Results from analysis of CHESS 2007 run data [1]
  4. Use of standard beamline quads for the tagger quad
  5. Progress on the electron beam requirements document
  6. Date for meeting with machine experts
  7. Update on communications with YERPHI colleagues


We went over the specification documents that have been posted so far on the wiki. Several suggestions were made to fill in missing parts

  • Top-level beam specification - add time resolution for tagging coincidences - R. Jones
  • Diamond specification - clarify the meaning of the rocking curve width for the entire crystal, increase the thickness tolerance to 5μr - G. Yang
  • Tagging spectrometer specification - Add tolerance information from the engineering design spec document - F. Klein

Everyone knows the specification pages they are in charge of, and will work on them for next meeting.

Questions from Engineering Firms

  • When will the magnetic field calculations will be updated?

Yang will import several significant geometry changes into his model and redo the 3D field map with TOSCA. Putting the Purcell gap into his model is more difficult because the gap is only a few mm, and the grid spacing is currently larger than this. Franz will do a 2D magnetic field calculation with a smaller grid size, and use that as a basis for estimating what smoothing of field roughness will be achieved by the Purcell gap. That will be used to smooth and irregularities in Yang's results.

  • What will the downstream end of the vacuum box look like?

We discussed the following picture for the parts of the vacuum box that see exit electrons.

  1. On the long exit slit where degraded electrons exit, simply install a 25 μm stainless steel foil that is glued to the upper and lower plates of the vacuum chamber.
  2. At the exit point of the main beam, weld a rectangular channel to the vacuum box that extends the vacuum region downstream another couple of meters. Franz will produce a concrete proposal and pass it to Tim for comments in time for the next meeting.

Results from CHESS

Yang has posted some slides on his results here. He will present them for discussion next meeting.

Standard beamline quads

This issue is now resolved. We can use a the standard beamline quad design as our specification for this component.

Electron beam requirements document

Work in progress, draft to be posted to the wiki one week before next meeting for discussion at next meeting.

Date for meeting with machine experts

Postponed until mid-March.

Communications with YERPHI colleague

They would like more details on the specifications for the Primakov pair spectrometer. Franz will inquire with Primakov collaborators and Jlab staff to get actual drawings and field maps for the dipole, vacuum chamber and telescopes.