General Meeting Summary 8/4/16

MAGNET UDPATE

Previously assumed that source of radiation is target and beam pipe - now also consider other radiation sources, e.g., low energy tail of beam, that could impact the open detector geometry on the floor
Additional radiation sources are specific for NPS experiments as the magnet is located close to the beam pipe and low energy particles may be deflected by fringe fields along beam line

Discussion about mitigation concept for fringe fields (pages 8-19 in Bogdan's magnet status slides)

Idea is to transport as many of low energy, secondary particles as possible through beam pipe to the beam dump
Consider a cutoff of 100-300 MeV for particles staying inside the flange and reaching the beam dump - 300 MeV would corresponds to 0.05% of beam power. Variation of the field in the beam line is on order +-0.5deg.
In current mitigation concept, the different experiment angle/kinematic configurations require different field compensation strategies - more global approach would be preferable if possible

There should be no field in the target
in some kinematics there are still fringe fields after the beamline for which compensation has to be designed

for HMS beam line need to mitigate fringe fields around the HMS snout (50 cm long) when the spectrometer is at small angles, e.g., 10 deg. Transverse fields are on order 200 Gauss.
To mitigate fringe fields around HMS (see Rolf's slides on fringe field configurations), one has to find a solution that does not affect HMS optics, i.e., how close to HMS Q1 could one put iron without affecting the spectrometer. Possible options include:

iron around snout - does not affect optics if iron at ~1m from target
magnetic cloak around snout like in: https://wiki.bnl.gov/conferences/images/e/e4/Nfeege_magcloak_committee_July_2016.pdf

Main coil design drawings finished and sent out for formal quotation - expect quote by 19 August
Still need corrector coil, but this one easier since does not require winding
Main yoke design drawings underway - other pieces like front field clamp, shelf attachment, and corrector (see Bogdan's slides, page 14) will be finished independently

CRYSTALS

Comparison of longitudinal transmittance of SICCAS crystals #16-45 as measured at CUA with Perkin-Elmer Lambda-950 spectrophotometer and at the company with unspecified methods
Comparison of longitudinal transmittance of SICCAS crystals #16-45 as measured at CUA and CRYTUR rectangular 20-cm long crystals as measured at Orsay/Giessen
Comparison of light yield at 18 degrees and with a 100 ns gate of SICCAS crystals #16-45 as measured at CUA and CRYTUR rectangular 20-cm long crystals as measured at Orsay/Giessen

SICCAS results show large crystal-to-crystal variation
Crytur results suggest large variations for first few crystals and much less after company made changes in doping - should include 18/19cm long rectangular crystals as well and compare T11-type crystals, which were made more recently to see if this trend is structural or method

DISCUSSION ABOUT TIME CRITICAL TASKS

Many decisions to be made in early fall, e.g., need to decide on final HV base/amplifier design, crystal dimensions, vendor, etc.

ITEMS FOR NEXT MEETING:

NEXT MEETING: THUR 1 SEPTEMBER, TIME: 9:00 AM (EDT)

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