General Meeting Summary 9/12/19

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  • 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


  • Temperature sensor was delivered - at ODU


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


  • 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