JEF meeting, June 14, 2019
Meeting time and location= 1:00 pm EST (JLab time) F228
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Magnetic shielding studies
Attendees: Josh, Wolfgang, Liping, Sasha, Simon
- Liping is working on finishing up an eta/eta-prime review article
- No news on NSF MRI proposal
- Progress on magnetic field shielding studies
- Poisson calculations indicate that the longitudinal field varies between 90 Gauss and 50 Gauss over the length of the FCAL
- Would need to place the insert crystals somewhere in the middle of the FCAL z-range -- offset face of crystal 10 cm downstream of face of FCAL?
- Sasha suggests pushing whole FCAL-II assembly downstream by 35 cm -- this puts the PMTs for the insert in a better magnetic field region but changes the acceptance of FCAL-II as a whole.
- Could in principle stack the lead glass crystals removed from the inner region at the outer radius of FCAL-II
- 3x3 prototype of soft-iron (1020 steel) tubes + mu-metal inserts
- 1020 could be annealed for ~20% improvement
- Length of housing still needs to be optimized
- mu-metal shielding thickness still needs to be optimized but promising results obtained with 350 micron mu-metal, could in principle increase another ~50 microns or so (50 micron material due at lab this week).
- Sasha and Josh looked at PMT response with and without sheilding
- At 4 Gauss longitudinal, saw 10% drop in amplitude without shielding
- With shielding, response flat up to 40 Gauss external field, 2-3% drop at 50 Gauss
- Still need to check transverse field impact
- Next step: address stacking and assembly of FCAL-II (frame design, distribution of stress
- Need to keep working on divider design.