BLTWG Meeting 03/26/2009

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  • Time: 9:30 EST
  • Place: EVO and ESNET (with telephone bridge)
  • Connecting: instructions are here
  • Present: Richard J., Igor S., Jim S., Tim W., Eugene C., Franz K, and Alex S.


  1. Tagger design internal review at JLab - Jim
  2. Microscope background rates estimates - Alex
  3. Checkout of updated photon beam simulation geometry - Richard
  4. Update on the spring 2009 CHESS run - Richard
  5. Update on phototube tests - Franz
  6. Review of working group manpower situation - Richard

Notes by R. Jones

Tagger design internal review at JLab

Tim has suggested that our tagger magnet specification be shown to an internal review panel at the lab, and have it critiqued before prospective vendors do. There was unanimous support for this idea. Tim and Jim have assembled a short list of people who would be good candidates for the panel, and will work with the Hall D group leader to arrange the best time. Middle to late May is currently being considered. Tim is going to draft a charge for the review. The presentations will be made by the engineering team led by Tim, but it was thought to be useful if Franz and Richard could be present, either in person or by video conference. RJ will send to Tim a list of preferred dates for the review.

Tagger background rates estimates

Alex has finished his technical note on tagger background simulations. It has been uploaded to docdb under gluex-doc-1228. New figures were shown for the updated background estimates for the microscope counters. As shown at the last meeting, the updated backgrounds in the fixed array vary from 10% of the signal rate near the end-point to about 4% in the mid-energy range, decreasing to 1% at the low photon energy end of the array. In contrast, the updated backgrounds in the microscope are about 0.5% of the signal rate in the region of the coherent peak at 9 GeV, similar to what was presented at the tagger review. Alex pointed out that his simulation includes a rectangular extension to the downstream end of the tagger vacuum chamber. Without this extension, the fixed array counters would have substantially more than 1% background at the low-energy end. This extension has not been implemented in the engineering drawings yet, but the engineers are aware that it is desired and will coordinate that update with the accelerator design people who are primarily responsible for the electron beam line from the tagger to the dump.

Checkout of updated photon beam simulation geometry

Richard is still working on verifying the HDDS geometry for the photon beam simulation. The contents of the collimator cave are finished, and the pair spectrometer is in progress. Improvements include a more refined description of the structure of the permanent magnet used as a sweep downstream of the primary collimator, and a refined description of the pair spectrometer geometry. So far, none of the changes are of the sort that would require rerunning the beamline background simulations.

Update on the spring 2009 CHESS run

Plans are coming together for the CHESS run coming up at the end of April. Participating in the run will be Richard Jones and Connecticut graduate student Igor Senderovich from Connecticut, and postdoc Pavel Nadel Turonski from Catholic U. Franz Klein hopes to come for a day or two, but has a conflict for most of the run period. We now have booked two rooms in the Fairview House guest house on the Cornell campus for the dates April 30 - May 7. The Connecticut group will bring the BNL diamond already attached in a frame that will mount on the goniometer sample post. The CU group will bring diamonds from their inventory. We need to verify that these diamonds will be mounted and ready for insertion into the goniometer.

Update on phototube tests

Franz is still waiting for the delivery of 2 Hamamatsu tubes for testing. These tubes have a faster response than the Photonis tubes that were originally envisioned for the fixed array. Franz will contact Hamamatsu and find out when these tubes will be delivered. The group plans to do bench tests with cosmic rays at CU and compare their response with Photonis tubes that they already have in hand.

Review of working group manpower situation

We spent some time at the meeting discussing the manpower crisis that is coming upon us with the departure of Jim Stewart for BNL at the end of April. There are at least two large gaps that we need to fill, one immediate and the other longer term but also critical.

  1. Jefferson lab beam line contact person - short term
    Having a laboratory physicist dedicated to the photon beam line really makes sense. The procurement of the tagger magnet will require continuous oversight and communication with the vendor if it is to happen on schedule. The vendor will have questions that require familiarity with the overall beamline design and a physicist's expertise to answer. The vendor's work will need to be carefully reviewed and monitored, otherwise delays and cost overruns will result. Paying a physicist's salary makes more sense than paying for changes.
  2. Pair spectrometer person - longer term
    The current design of the PS has resulted from a collaboration between Jim Stewart and Hrachya Hakopian from the Yerevan Physics Institute. The YERPHI group wants to remain involved in the project, but they cannot afford to send a member of their group permanently to Jefferson Lab to take charge of all aspects of the project. We need a person or group to take charge of this project, who will work with the YERPHI group, but who can either be at the lab or close enough that communication with laboratory designers and technicians can be frequent and effective.

This list is not exhaustive. Manpower estimates for parts of the tagger and beamline infrastructure that have been assigned to Connecticut and Catholic U are already present at some level in the P3E schedule. These estimates need to be reviewed in preparation for the Lehman review later on this year.

Other news from Jefferson Lab

Jim has met privately with laboratory staff to find out more details about the scheme we will use for feeding back the photon beam spot location signal from the active collimator to the electron beam position stabilization system. He will arrange to have a second meeting on this subject that will involve a larger circle of people. This should be done soon, because preparation for the Lehman review will soon begin to fill people's schedules.