The Results of 10 Additional PMT Tests

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The Results of 10 Additional PMT Tests

• Timing of afterpulse
• ADC readout
• 3. Conclusion

TTU HEP Group Meeting, Apr. 14, 2004
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Test of R7525 PMT(CA1522) shows afterpulse. Need
to confirm if afterpulse is general behavior in
other PMTs.
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1. Timing of afterpulse
a)
b)
c)

• 0066, 0068, (1522)
• 0405, 0515, 1609
• c) 0872, 1078, 1313, 1817, 2108

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2. ADC readout

• Pulse height of afterpulse does not depend on
  main pulse (top).
• Afterpulse rate is higher in c) type, middle in
  b) and lower in a)(bottom).

a) 0068
b) 0405
c) 1078
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Most probable explanation of afterpulse
Ionization of the residual gases in the tube
gives rise to afterpulse. The usual ions are H2,
He and CH4. They cause afterpulses which have
0.3, 0.4 and 1ms transit times.
-- photomultiplier tubes, Philips Photonics
3 peaks in timing distribution may be matched to
ions. Test with type C) PMT under He abundant
condition can be tried. -gt expect that second
peak will increase before/after He blowing.
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Energy estimations for the afterpulse
Expect 0.25 p.e./ GeV for the HF calorimeter.
(I) Based on ADC count of the afterpulse
150 ADC count after 100 times amplified PMT
output. 0.25 pC/count for Lecroy 2249W. 150 x
0.25 pC 37.5 pC Since PMT output was amplified
100 times, it becomes 0.375 pC. If we assume 105
gain for the PMT, the charge at the PMT
cathode is 0.375x10-17 C. The number of p.e. at
the cathode is (0.375x10-17)/(1.6x10-19)
23.5 p.e. ? 94GeV.
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(II) Estimate base on pulse shape

• 500mV pulse height with 10ns width after 100
  times amplification.
• 5mV PMT output
• I Q/Dt V/R1/2 (50ohm oscilloscope
  termination)
• Q V/R1/2dt (5x10-3)/501/210x10-9
• 0.5x10-12C 0.5pC
• of p.e. at PMT cathode 0.5x10-12/(1.6x10-19
  x 105)
• 31.25 ? 125GeV

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(III) If 10GeV is deposited in a tower,
10 x 0.25 p.e./GeV 2.5 p.e. 2.5 x 1.6 x 10-19 x
105 4 x 10-14 0.04 pC After 100 times
amplification, 4pC. Since 0.25pC/count in Lecroy
2249W ADC, 4pC gt 16 ADC counts
Afterpulse rate at 10GeV (main signal)

• 0.06
• 0.10
• c) 0.72

cause 100GeV afterpulses.
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3. Conclusion Plan
Test with another type of PMT -gt We already
know that there is afterpulse for other PMTs.
-gt Also need to quantify the level. Operate PMT
under He abundant condition. -gt To
understand(confirm) the source of afterpulse.