The Results of 10 Additional PMT Tests. Timing of afterpulse ADC readout 3. Conclusion. TTU HEP Group Meeting, Apr. 14, 2004. PMT serial # used in the test. }. CA0066 CA0068 CA0405 CA0515 CA0874. From batch 1~5. }. CA1078 CA1313 CA1609 CA1817 CA2108. From batch 6~10.
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The Results of 10 Additional PMT Tests
TTU HEP Group Meeting, Apr. 14, 2004
PMT serial # used in the test
From batch 1~5
From batch 6~10
Test of R7525 PMT(CA1522) shows afterpulse.
Need to confirm if afterpulse is general behavior in other PMTs.
1. Timing of afterpulse
2. ADC readout
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.
-> expect that second peak will increase before/after He+ blowing.
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.
(II) Estimate base on pulse shape
I = Q/Dt= V/R*1/2 (50ohm oscilloscope termination)
Q = V/R*1/2*dt = (5x10-3)/50*1/2*10x10-9
= 0.5x10-12C = 0.5pC
# of p.e. at PMT cathode = 0.5x10-12/(1.6x10-19 x 105)
= 31.25 125GeV
(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 => 16 ADC counts
Afterpulse rate at 10GeV (main signal)
cause ~100GeV afterpulses.
3. Conclusion & Plan
*Test with another type of PMT
-> We already know that there is afterpulse for other PMTs.
-> Also need to quantify the level.
*Operate PMT under He abundant condition.
-> To understand(confirm) the source of afterpulse.