BLTWG Meeting 12/6/2007
From GlueXWiki
- Time: 10:00 EST
- Place: VRVS and ESNET
- Present: Aschenauer, Jones, Klein, Whitlatch, Yang
The agenda for this meeting was to review the status of all of the major systems under the oversight of the GlueX Tagger/Beamline working group, with the purpose of setting short-term goals and target dates for accomplishing things that must be completed in preparation for the 2008 Lehmann Review.
Contents
Tagger Design
- The tagger specification and Statement of Work documents for the 100% tagger engineering design bid package have been completed and sent on to purchasing for review. The 12GeV Program Office has already approved the procurement.
- Tim is working on the tagger interface drawings that he has made, as a final piece in the bid package. Discrepancies between different sources of information were pointed out in email exchanges, are being resolved.
- Elke will post the final revisions of the Tagger Specification and Statement of Work documents at the usual place on the wiki.
- The first major milestone in the monitoring process set up for this project is in the March-April 2008 time frame. This will be finalized during negotiations with the firm who wins the contract.
Interface with Accelerator
- Richard has written a document ``GlueX Requirements for 12 GeV Electron Beam Properties'' (gluex-doc-646). This document summarizes the GlueX physics requirements for the 9 GeV photon beam, and derives from these the requirements for the 12 GeV electron beam. The final section shows how these requirements can be phased in gradually within the context of the GlueX commissioning plan.
- Discussion of these requirements with the CASA group raised major concerns with two major points: emittance and halo. The former describes the r.m.s. size of the central intensity peak of the beam, while the halo describes the intensity at larger radius where it exceeds the gaussian fit. The concern over emittance subsided in early 2007 when the nominal beam emittance figures went down by a factor ~2 after a computational error was found. The halo concern remains.
- In Spring 2007 the CASA group produced an improved halo model based on a ray-tracing simulation through the accelerator. The GlueX tagger backgrounds have been resimulated using this halo model. The results allow the GlueX halo specification to be relaxed by one order of magnitude, while still adhering to the basic criterion of less than 1% background in the tagging counters.
- Richard needs to update the document to incorporate the two developments described above. End of January, 2008 is the target date for an updated version of gluex-doc-646.
- Elke will organize a meeting with the relevant people from CASA, accelerator division, and GlueX to review the electron beam requirements, with a goal of agreeing on a specification for the Hall D electron beam properties. A target date of the end of February is set for this meeting.
Photon Beam Collimator and Shielding
- Richard has produced the following documents which are a part of Tim's 35% design drawing library from the 2007 Lehmann Review.
- Detailed drawings of the active collimator
- Layout drawings of the complete collimator cave and contents.
- Collimator cave floor loading plan.
- The drawings of the beam line shielding plan (#2 above) are only sketches. Franz Klein will take these sources and turn them into 80% engineering drawings. A target date of end February 2008 is set for this task.
- Richard has produced an overall alignment plan for the Hall D photon beamline. This plan should be reviewed at the meeting with CASA and accelerator division regarding electron beam requirements.
- Alignment of the primary and secondary collimators will require sub-millimeter precision. The primary collimator should be mounted on a translation stage with both X and Y motion sufficient to completely move the collimator out of the beam. The 75% drawings will include the design of the collimator support elements and indicate what degrees of freedom require remote control adjustment.
Tagger Hodoscopes
- Broadband array - Franz plans to do 100% design drawings of the broadband tagging hodoscope prior to the 2008 Lehmann review. The drawings will include the support structure for the broadband counters and the table on which the microscope will be supported. A rail for transporting a mobile radioactive source along the entire length of the broadband array will be included in the design. A target date of mid-May 2008 is set for the completion of these drawings.
- Microscope - The following drawings exist as a part of the 35% engineering design for GlueX.
- UConn students will begin with these drawings and develop them further to the point of a 75% design. He will consult with the UConn Physics machine shop supervisor on what level of detail is required for 75%. He also requests from Tim an example of a 75% design to help clarify what level of detail is required. The target date of mid-May is set for the completion of these 75% drawings for the microscope.
- Alignment of the microscope will require sub-millimeter precision. The 75% drawings will include the design of the supports and whether or not remote control adjustment to the alignment is required.
Pair Spectrometer
- We have a shared interest with Primex in this device. Elke has contacts within Primex whom she will approach with the proposal that the Primex pair spectrometer be incorporated into Hall D as an integral part of the photon beam instrumentation.
- Members of the Yerevan group have expressed interest in working on some aspect of the polarized photon beamline instrumentation. We propose that they be asked to come up with a specification for the pair spectrometer and associated hodoscope counters. This specification will form the basis for a search for an existing magnet that might meet our need for a pair spectrometer.
- Richard will make contact with the Yerevan group and suggest that they focus initially on the specifications of the pair spectrometer, and not worry too much right now about an engineering design for such a magnet.
- Progress towards arranging for a visit from the Yerevan group to Jefferson Lab is slow. Richard will make contact with YERPHI colleagues to help move along the process of applying for visas, buying tickets, etc.
Diamond Radiators
- Yang has started to analyze the data taken at CHESS last month. Two of the diamonds we studied have very narrow rocking curves on the order of 15 microradians, and a third has a width of 30 microns. All three of these are of sufficient quality for R&D on thinning and mounting.
- Mounting continues to stand out as a problem. Yang noticed that rocking curves are often wider when rocking around an axis along the mounting wires than along an orthogonal axis. This suggests that the wire supports are unstable along this direction. This can be studied optically using a visible laser.
- Our present experience with thin diamonds is limited to one example, which turned out to be a bad one. We want to produce several 20 micron diamonds and study them using a variety of mounting techniques. The three diamonds of reasonably good quality that were examined at CHESS in 11/2007 belong to Element Six. Yang will contact Element Six and find out if they are willing to sell them to us, and what the price will be.
- Assuming we can buy them for an affordable price, we need to investigate firms that will be able to thin them for us. Several possibilities came up during discussion
- Element Six may be willing to thin them, as they have before.
- Another US company Diamond Knives may be willing.
- The source group at BNL is building up the capability in-house to thin diamonds using ion bombardment.
- Glasgow University has ion beam facilities that might be used. If we learn that experiments at BNL are successful, we might try it ourselves.
- Yang will investigate options 1 and 2 above. Richard will follow up on his contact with the BNL source group. Both will report on progress at the next working group meeting.
