Thanks to R. Snyder, L. Kaufman, D. Lhuillier, and S. Bailey

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Luminosity Monitor 250 Hz Reversal R.
Suleiman Qweak Collaboration Meeting, 14 October
2005
1. Lumi Photodetector Photodiode vs. PMT Base
with Gain 1 2. PMT Linearity Studies 3. 250
Hz Reversal and the Pockels Cell Response
Thanks to R. Snyder, L. Kaufman, D. Lhuillier,
and S. Bailey
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Gain 1 Photodetector

• R2046 PD (with quartz window) or PD025 will cost
  more than 4,000 each.
• Instead use a PMT Base will operate at gain1
  and 1,000,000
• Hamamatsu R375 2 inch, quartz window,
  multi-alkali, 10-stage, 1,100 each.
• Photonis and Electronic Tubes have similar PMTs.

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PMT Base with Gain 1
- Signal picked off from the first dynode
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PMT Linearity Test
- A non-linear response of a PMT to a given
signal N is parameterized as
where the refers to the two helicity states,
then
with
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Linearity Test Procedure

• Continuous diode simulates the beam nominal
  running.
• Pulsed diode is turned on/off at the helicity
  reversal frequency generating an asymmetry of the
  size of the ratio of the two diodes amplitude.
• The PMT output is integrated and is measured
  for 4 different filter transmissions 80, 60,
  40, 20.
• A perfectly linear PMT will measure the same
  for all filter settings.

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HAPPEX Linearity Test Setup

• Tested HAPPEX (main detector and Lumi) PMTs
• Results look like

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vs. continuous Diode Signal in ADC channels

• Problem with the
• non-homogeneity
• of filters

• Will improve setup to measure linearity to at
  least 0.1
• Will test R375 Base (gain1) at 30 Hz and 250
  Hz
• Will use the TRIUMF (old-style) I/V preamp box
  plus
• V/F plus scaler. Could try out the new Qweak I/V
  if available.

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250 Hz Reversal the Pockels Cell Response

• 250 Helicity signal is now available in the laser
  room.
• T-Settle available 500 us, 100 us, 80 us or 60
  us.
• Pockels Cell alignment HV, Degree of Circular
  Polarization (99.8) are identical to 30 Hz
  reversal.
• Did oversampling (OS) runs.

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250 Hz OS 1 T 80 us
30 Hz OS 1 T 500 us
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250 Hz OS 13 T 80 us
30 Hz OS 13 T 500 us
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250 Hz OS 13 T 80 us
30 Hz OS 13 T 500 us
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Conclusions and Outlook

• Tests of air light guide transmission at
  Virginia Tech.
• Prepare a lumi prototype (with quartz, air light
  guide, and phototube picked off at first
  dynode) for use sometime during the G0 backangle
  run (summer - fall 2006).
• Study R375 PMT Base (gain 1) linearity.
• More work in the laser room to study 250 Hz
  helicity reversal. Figure out the best T_settle
  (probably 200 us 5 of the time) that
  minimizes charge asymmetry and position
  differences.