BLTWG Meeting 02/26/2009

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


  1. Review of notes from last meeting - Richard
  2. Report on the Installation Review - Tim
  3. Version 1 installation schedule - Jim
  4. Update on the tagger background simulations - Alex
  5. Progress at BNL in laser ablation of diamonds - Richard
  6. Tagger dipole field uniformity specification - Jim
  7. Feedback on updated interface drawings - Tim
  8. Manpower for the spring 2009 CHESS run - Richard
  9. Plans for beam tests in 2010 - Franz

Notes by R. Jones

Report on the Installation Review

Tim reported on the feedback received from the internal Installation and Safety Review of Hall D that took place last week at the lab. The final report from the committee is available here [1]. The first recommendation is that the Hall D group hire a technical work coordinator as soon as possible. One outcome from the review is that we need better estimates of contributed manpower from universities in order to convince the reviewers at the Lehmann Review this summer that we are going to be able to do the construction and installation in the time that is shown on the schedule.

Installation Schedule Version 1

Jim walked us through the construction and installation schedule for the tagger and major photon beamline equipment [2]. He highlighted that the lab will begin the changeover from 6 GeV to 12 GeV in two shutdown periods, a short one followed by a longer one, right around the same time when the tagger magnet is to be delivered to the lab. Between the two shutdowns the construction of the electron beam dump and shielding will be going on in the tagger hall. He warns that this will be a very busy period for lab-wide service groups like the survey group, riggers and crane operators, electricians and the like. Getting this kind of help during the installation period will require a good bit of advance scheduling and planning. The schedule currently includes the tagger and photon beam line through the collimator cave and pair spectrometer down to the entrance to the target, and again, in back of the FCal to the photon beam dump. He expects that Franz and I will have to produce our own construction schedules with the same level of detail for the tagger hodoscopes and the pair spectrometer counters, and then merge those independent tracks into the existing schedule for checkout and installation that takes place once the detectors arrive at the lab.

Update on the tagger background simulations

Alex walked us through an early draft of his tagger background simulation technical note [3]. Background estimates are now considerably larger (factor 2-3) than the earlier ones that were done using the coherent bremsstrahlung generator. The new rates are considered reliable, except for the possibility of additional background from synchrotron radiation below the Geant cutoff. RJ will look into making an estimate for this as soon as Alex completes the Geant study. Alex will repeat the background estimates for the microscope that he has made for the fixed array, and include those results in his final report.

Progress at BNL in laser ablation of diamonds

Richard presented some slides that John Smedley shared with him showing recent progress by the BNL group in thinning diamonds [4]. Things are looking very encouraging so far. It is reasonable to hope that this laser ablation technique will enable us to produce 20 micron diamonds with arbitrarily thick edges, with essentially no risk in terms of breakage or irreversible surface damage. It seems that this statement holds true, whether or not we are able to use CVD diamonds as radiators, or whether we have to fall back on the pick-and-chose HPHT diamond selection process.