JMU Dark Current Tests
By: Kevin Nash
JMU Dark Current Tests
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1. Our setup and data taking procedure
2. Current progress report
3. Data analysis
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Full comparison
Precision and slot comparison
Warm up characteristics
High voltage curve
4. What’s next
JMU Dark Current Setup
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(fig.1) To expedite the rate of testing progress, bar codes are applied to all
tubes which lets the user enter the PMT serial code instantly.
(fig.2-fig.3) Photomultiplier tubes are inserted into the housing, taped closed,
and covered with a sheet prior to testing.
(fig.4) After warm up, the tubes are tested with the use of a Labview program
that monitors the Picoammeter.
After testing, the values are recorded into the MySQL database for future
analysis.
Progress Report
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Currently the JMU team has
completed dark current tests on seven
out of the ten total batches.
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749 tubes have been tested and
recorded out of the total 1200
Based on the current rate of progress
of approximately 100 tubes per week,
all tubes will be tested by early April
All Dark Current Comparison
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Average JMU dark current was 0.199nA
Average Hamamatsu measured dark current was 0.486nA.
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JMU dark current values are measured an average of 0.291nA lower than the
manufacturers tests
JMU dark current values range from 0.0062nA to 0.951nA for a total range of
0.945nA compared to the manufacturers range of 3.07nA
The chi-square from the mean was 8.96 for JMU tests and 43.66 for the
manufacturer tests
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This would suggest that the JMU tests are more precise
A Closer Look
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The discrepancy is systematic.
All Dark Current Comparison
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Both Hamamatsu and JMU dark current
tests appear to follow a poisson distribution
Clearly, the JMU tests are more precise
Slot Comparison
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This is a comparison of the five testing slots used in the JMU dark current tests using the
same pmt: serial CS2860 and six data points per slot.
The average dark current for this PMT was 0.171nA
The random error for these tests was +/- 0.045nA
There is little or no systematic error from slot to slot
This would suggest a maximum random error of 26.3%.
Fitting a Gaussian to the data approximates a standard deviation of 0.032 nA
Warm up Behavior
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Test of all 5 slots during 30 min warm up (fig.1) consists of 7 data
points per PMT
Test of a single PMT during 30 min warm up (fig.2) consists of 60 data
points
Both suggest relatively standard operating conditions after 15-20
minutes of warm up
Both JMU and Hamamasu measured dark current values are tested
after 30 minutes of warm up .
Dark Current HV Curve
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A comparison of the typical high voltage dark current variation
versus the JMU measured dark current variation.
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Conclusion: The voltage range for the dark current tests is
generally not highly effected by ohmic leakage or regenerative
effects, and is mainly due to thermionic emission.
The Future
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Base soldering for all 1200 tubes (fig.1-fig.2)
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Base testing (fig.3)
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Base to be soldered to socket, using the spring and PVC tube for pressure and
spacing within the PMT housing.
This apparatus will be used to test the uniformity of the voltage between the dynode
stages.
Gain testing through high voltage curve (fig.4)
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Design and implementation of an even light source and fiber optic network.