General Meeting Summary 9/12/19

HV DIVIDERS

• Background on and recent tests of active divider (V. Popov design)

• Active setting changes two transistors on last dynode, usually used for high rates, compared to Hamamatsu passive setting; also includes pre-amp to reduce anode current
• Recent measurements show:

• anode current with active divider is 1/2 of that with passive Hamamatsu divider
• non-linearity for bypassed amplifier is on order 2% (similar to Hamamatsu)
• non-linearity increases to ~4-5% if include amplifier with gain 3

• Based on recent estimations (see Bogdan's slides) anode current for some NPS experiment settings may be 250uA, exceeding the Hamamatsu PMT specs (anode limit=100uA) - even if the active divider cuts the anode current by 1/2, it would still be ~125uA, at the upper end of the specifications

• Discussion of NPS experiment specifications

• Linearity - how important?

• if know gain curve for whole assembly, non-linearity could be corrected - need good monitoring system

• Anode current - more detailed estimate or measurement

• include QE of PMT used
• background simulations ongoing
• data analysis from Hall D measurement may also provide information; here, the LMS was not covering the full dynamic range - corrected the beam for 1.5-10GeV/c, but missing the lower energy range

• Discussion of two HV Divider optimization options: 1) Reduced gain/bypassed amplifier, 2) Shorten dynode (no amplifier)

• Complexity of work

• in both cases would keep form factor and connectors same
• Reduced gain (change resistor, currently have gain 25)and bypassed amplifier (resistor, jumpers) require mostly labor, cost of parts is negligible
• Shorten dynode may require a new, redesigned PCB (additional testing needed to decide) and re-soldering sockets; overall may require both funds for purchasing new PCB with redesign and labor

• Time to implement either option: 4-5 months

• need to check on availability of resources

• Note that the active divider (designed by V. Popov) may not yet fully optimized - similar issue with tagger hodoscope; Hall D expects to have a new version in November; NPS may benefit from these optimizations

• Action Items:

• Estimate 1) impact of non-linearity on physics for NPS experiments, 2) more detailed estimate of anode current
• Test of shorten dynode option - based on results, decide in January which option to implement

MAGNET

• Temperature sensor was delivered - at ODU

CRYSTALS

• Draft paper posted - please send comments; goal is to submit for publication by end of the year

SIMULATION - DOSE PROFILE

• Magnet position updated
• Background: DVCS shower max 6-7 radiation lengths and background dose only decreases by factor ~4

Next steps: evaluate shielding material and locations

NEXT MEETING: THURSDAY 3 OCTOBER AT 9:00AM (ET)