PMT gain check at Indiana University
Test setup inside dark box
LED
whi
te p
aper
PMT # JT0298channel #2 (per HPK numbering)
OTHER CHANNELS MASKED WITH BLACK TAPE
oscilloscope
pulser
trigger in
C.R.T. Proto Pogo Pin HVB
Direct connection of anode to MMCX/cable, with 10 kΩ bleeder resistor to ground.Scope’s voltage integral / 49.75 Ω is PMT charge.
The setup Integrate charge in fixed gate, triggered by pulser that fires LED.No discriminator / no cuts. No external amplifiers.
production front board
integration gate 7.5 ns
blue trace is PMT charge (since t = 209 ns)
purple histogram is charge at end of the gate interval
↑ 80fC
Typical results The LED is slow of course (~3ns width), but it is cheap
↑ 80fC
Typical single event with signal
A few more details in case you want to know…• Scope set to 800 MHz bandwidth limit, 2 mV/div• Sampling at 20 GS/s (integral = 150 sample points sum)• Interpolation between sample points is turned off. (Worry is, this might
cause some unknown error in the integral.)• LED pulser rate 500 Hz• From look at single-shot acquisitions, even at very low amplitude such
that only a few % of events are not pedestal, there is a sizeable fraction of double-pulse events. Either this is afterpulsing in the PMT, or a characteristic of my LED source. In latter case, my results are contaminated with 2-photon events. Probably it doesn’t make a big difference, but this needs to be considered.
• It is useful to note that math trace does not saturate to screen display limits. As long as ADC (ch1 display) does not saturate, all the data of that event is good. I adjust ch1 gain V/div so that it very rarely saturates.
↑ 80fC
A double pulse event – they are not extremely rare…
3150 V
Old results for reference – suffers from binning artifacts
3150 V
Old results for reference – suffers from binning artifacts
3200 V
Improved analysis:• Integer waveform data stored from scope• Integer sum for charge• Binned as integer (here bin=charge/4)• As before, then fit pedestal and subtract it,
see next slide
But, fewer events here (0.5 vs. 7.5M…)
pedestal σ = 4.13 fC
3200 V
61900 hits (12%, I should lower LED intensity…)
mean 65.6 fC (410 k electrons)
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