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. 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

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The results of 10 additional pmt tests

The Results of 10 Additional PMT Tests

  • Timing of afterpulse

  • ADC readout

  • 3. Conclusion

TTU HEP Group Meeting, Apr. 14, 2004


The results of 10 additional pmt tests

PMT serial # used in the test

}

CA0066

CA0068

CA0405

CA0515

CA0874

From batch 1~5

}

CA1078

CA1313

CA1609

CA1817

CA2108

From batch 6~10

Test of R7525 PMT(CA1522) shows afterpulse.

Need to confirm if afterpulse is general behavior in other PMTs.


The results of 10 additional pmt tests

1. Timing of afterpulse

a)

b)

c)

  • 0066, 0068, (1522)

  • 0405, 0515, 1609

  • c) 0872, 1078, 1313, 1817, 2108


The results of 10 additional pmt tests

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


The results of 10 additional pmt tests

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.


The results of 10 additional pmt tests

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.


The results of 10 additional pmt tests

(II) Estimate base on pulse shape

  • 500mV pulse height with 10ns width after 100 times amplification.

  • 5mV PMT output

    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


The results of 10 additional pmt tests

(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)

  • ~0.06%

  • ~0.10%

  • c) ~0.72%

cause ~100GeV afterpulses.


The results of 10 additional pmt tests

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.


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