tests with jt0623 & jt0947 at indiana university nagoya pmt database test results for jt0623 at...
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Tests with JT0623 & JT0947 at Indiana University
Nagoya PMT database test results for JT0623 at 3220V:
This tube has somewhat higher than usual gain. 5×105 is far from the measured points. Therefore I first try to look at the lowest voltage measurement point.
G. Visser 4/24/2015 (latest update)
I looked at channel 2 and channel 3, according to Hamamatsu numbering
Channel 2
Channel 3
This is the same dataset analyzed on following pages. 2,200,000 events.
note there is sometimes ADC saturation
Scope data exported as integer (ADC units), and then summed as integer. No binning artifacts (except for real DNL of course).
crosstalk events
P.O.U.W. (pulses of unusual width), mostly two-photon events
ADC saturation
ADC saturation crosstalk events (bipolar shape)
Pedestal fitf(x)=a*exp(-(x-x0)**2/(2*σ**2))a= 157511. +/- 203.5x0= 315.063 +/- 0.008σ=5.278 +/- 0.008
2083870 events in pedestal
signal 1-2083870/2181674 = 4.5%
Rescale x with pedestal mean and theoretical scale charge/icharge = 0.0062069 Melectrons (from assumed load resistance, scope V/div and sample rate).Fit whole curve (from 0.11 to 3.1 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + pedestal fit from before (as a fixed background).Really should consider electronics noise in signal, fixing same sigma as pedestal, this is oversimplified here.
Signal in fitg(x)=b*x**p*exp(-x**q/c)b=937.86 +/- 43.29p=0.54515 +/- 0.02452q=1.43851 +/- 0.03820c=1.01857 +/- 0.04935
103097 events in signal (102442 to 3.2 Melectrons)
(expected 2181674-2083870=97804 + the lost tail) – good agreement
mean signal size 0.972 MelectronsJT0623/ch23220 V
Pedestal σ = 0.03276 Melectrons
Same plot except on linear scale
mean of all(as above)
mean for >0.13
mean for >0.25
threshold (e.g. of discriminator if used) can make a 10% difference
JT0623/ch23220 V
Repeated all the above on another, independent data run 2.2Mevents, same HVB voltage.
Result: Mean charge 1.04 Melectrons.
Probably this is representative of +/-5% or so statistical error in the method. Some of this might be due to sensitivity to “arbitrary judgement” tuning fit limits.
Next, we look at the nominal 5x105 gain voltage for this channel. From database, the gain fit equation is G=exp(0.004891*V-15.59) and so we need to set to 3046 V.
Note that is a ~180 V extrapolation from the measured datapoints (which span 200 V). I don’t know what accuracy is expected…
Mistake was made – that was ch3 nominal 5x105 gain voltage. Oops.
My results from 3046 V are on following three pages. I don’t show all the initial analysis details just the end results, but method of analysis was similar. Scope is now set to 2 mV/div.
Charge histogram method as before.Fit pedestal first, then fit whole curve (from 0.08 to 1.22 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit.
Signal in fitg(x)=b*x**p*exp(-x**q/c)b= 2612.97 +/- 359.6p= 0.73315 +/- 0.04844q= 1.29602 +/- 0.04679c= 0.20943 +/- 0.005052
89585.9 events in signal (89291.1 to 1.27 Melectrons)
[We expected 2200000 -11574(cut) -2103340(pedestal fit) = 85086 events in signal. Good.]
mean signal size 0.353 Melectrons
JT0623/ch23046 V
Pedestal σ = 0.024164 Melectrons
JT0623/ch33220 V
Pedestal σ = 0.03021 MelectronsCharge histogram method as before.Fit pedestal first, then fit whole curve (from 0.10 to 3.00 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit.
Signal in fitg(x)=b*x**p*exp(-x**q/c)b = 1022.25 +/- 42.42p = 0.46961 +/- 0.02161q = 1.60819 +/- 0.03938c = 0.84900 +/- 0.03183
93270 events in signal ( 4.2% )[We expected 2200000 −19542(cut) −2088910(pedestal fit) = 91548 events in signal. Good.]
mean signal size 0.758 Melectrons
Summary / comparison with Nagoya PMT database test results(Nagoya channel number = Hamamatsu channel number − 1)
Nagoya IU ratio Nagoya/IU
ch2 @ 3220 V 1.61 Me 0.972 Me 1.67
ch2 @ 3046 V 0.831 Me (projected) 0.353 Me 2.35
ch2 @ 2913 V 0.500 Me (projected) tbd
ch3 @ 3220 V 1.15 Me 0.758 Me 1.52
ch3 @ 3046 V 0.500 Me (projected)
ch3 / ch2 @ 3220 V
0.714 0.780
• This seems to indicate a discrepancy in measured points, by about a factor 1.5• It’s necessary to try to confirm calibration of IU method by an independent
method, see following slides – results seem confirmed• It seems there is a further discrepancy in projecting from measured points
down to 0.5 Me gain level. In my opinion the gain fit function G=G0eαV does not have enough freedom to match the real data.
We may suspect some large >>5% error in the calibration here if:• The load resistance, or scope voltage or time scale is out of calibration? (Not likely!)• Summing the scope ADC samples doesn’t give a good estimate for charge integral?
(i.e. Nyquist vs. Riemann)• There is charge lost elsewhere? (Stray capacitances remove something from pulse
and only comes back slowly? Not likely but…)• Integration gate not correct? (But clearly it’s ok in scope photo!)• Fit is not good and so mean of fit doesn’t estimate mean of signal data? (But it looks
reasonable I think we all agree…)• Bug in scope, or in analysis?
To check this, I set up the LED pulser to a much higher rate (500 kHz rather than 500 Hz used above). Then directly measured the anode current on a picoammeter, and used the scope method to estimate only the fraction of signal events but not the mean amplitude. To make a better comparison, I do not cut the multi-photon events from the data.
The LED amplitude and PMT gain may be shifting between 500 Hz and 500 kHz. Also the LED is not in precisely same location as before (I had to remove bleeder resistor from the setup, disturbing it). Therefore what we want to compare is the gain determined from picoammeter current and scope-method signal fraction, to the gain determined by scope method on the same 500 kHz data set.
Results on following slides…
JT0623/ch33220 V500kHz2-photon not cut
Pedestal σ = 0.03032 MelectronsCharge histogram method as before.Fit pedestal first, then fit whole curve (from 0.094 to 3.00 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit.
Signal in fitg(x)=b*x**p*exp(-x**q/c)b = 1518.08 +/- 47.6 p = 0.46552 +/- 0.01662q = 1.60150 +/- 0.03092c = 0.936993 +/- 0.02918 152053 events in signal ( 6.98% )[We expected 2200000 −22972(cut) −2048550(pedestal fit) = 128478 events in signal. Moderate agreement, (20%), maybe due to distorted pedestal from baseline wander at the high rate.]
mean signal size 0.807 Melectrons
Current method (using Keithley #2485):LED on: −4.793 nALED off: +0.024 nA (just background/offset of the meter)Calculated mean signal:4.817 nA/(500 kHz * 6.98%) = 0.862 Melectrons
This is pretty good agreement (0.862/0.807) with the integrate/fit method, I think. Some extra current is to be expected from afterpulsing, which is outside the integration gate.
Move on to JT0947
Nagoya PMT database test results for JT0623 at 3010V:
I looked at channel 2 and channel 3, according to Hamamatsu numbering
Channel 2
Channel 3
This is from the newer procedure, where measured data comes closer to 5e5 gain,no large extrapolation is involved.
JT0947/ch33010 V
Pedestal σ = 0.02332 MelectronsCharge histogram method as before.Fit pedestal first, then fit whole curve (from 0.072 to 0.70 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit.
Signal in fitg(x)=b*x**p*exp(-x**q/c)b = 12372.9 +/- 2999p = 0.94528 +/- 0.07329q = 1.24050 +/- 0.04934c = 0.0901407 +/- 0.00088
137640 events in signal ( 6.3% )[We expected 2200000 −12612(cut) −2062040(pedestal fit) = 125348 events in signal. Good.]
mean signal size 0.197 Melectrons
JT0947/ch33210 V
Pedestal σ = 0.02805 MelectronsCharge histogram method as before.Fit pedestal first, then fit whole curve (from 0.11 to 2.36 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit.
Signal in fitg(x)=b*x**p*exp(-x**q/c)b = 1220.41 +/- 44.58p = 0.36669 +/- 0.01891q = 1.70531 +/- 0.03849c = 0.78737 +/- 0.02436
139034 events in signal ( 6.3% )[We expected 2200000 −22086(cut) −2042780(pedestal fit) = 135134 events in signal. Good.]
mean signal size 0.664 Melectrons
Summary / comparison with Nagoya PMT database test results(Nagoya channel number = Hamamatsu channel number − 1)
Nagoya IU ratio Nagoya/IU
JT0623 ch2 @ 3220 V 1.61 Me 0.972 Me 1.67
JT0623 ch2 @ 3046 V 0.831 Me (projected) 0.353 Me 2.35
JT0623 ch3 @ 3220 V 1.15 Me 0.758 Me 1.52
JT0623 ch3 / ch2 @ 3220 V
0.714 0.780
JT0947 ch3 @ 3010 V 0.63 Me 0.197 Me 3.20
JT0947 ch3 @ 3210 V 1.72 Me 0.664 Me 2.59