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PMT response at high rates (and a final surprise)

PMT response at high rates (and a final surprise). A. M. Baldini INFN Pisa. photon charge and LED dependence on beam intensity. What we saw during the test:. UV. Beam on. off. on. BLUE. Beam on.

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PMT response at high rates (and a final surprise)

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  1. PMT response at high rates (and a final surprise) A. M. Baldini INFN Pisa

  2. photon charge and LED dependence on beam intensity What we saw during the test: UV Beam on off on BLUE Beam on

  3. One LED simulates crowding (50 KHz of 5 MeV pulses) due to neutrons and another one is read Neutrons rate during normal runs Ia 0.6 A, Ib 70 A   6 minutes Start crowd. Stop

  4. Cryogenics test facility at Pisa

  5. Method of the tests • PMT tested in Ar gas at several temperatures (30 -120°C) • Test LED (blue) pulse usually at 10-50 Hz, 300 mV, 20 ns wide • Crowding LED (blue) 300 mV, 10-40 KHz, 20 ns wide (Ia=1,10 A) • Crowding turned on and then off after some time • One old kind PMT (6041) and two new ones tested

  6. 30 10 50 Time (s) 60 20 120 Time (s) OLD (6041) PMT at –105 °C I crowding= 0.8 A  = 66 sec

  7. OLD (6041) PMT at 25 °C Same crowding as previous slide

  8. 200 100 300 Time (s) New (9288) PMT: TB0171 at several crow. Currents at T=-110°C TB0171 at 4,8, 12, 16 A Two effects present: cold + gain variation (non linearity)

  9. Gain variation as a function of photocathode illumination Taken from the photonis PMTs handbook

  10. 200 100 300 Time (s) TB0171 at room temperature (gain variation only) Icrowd=4A

  11. Effect vs temperature for the three tested PMTs TB0204 4A TB0171 4A TB0171 8A OLD 0.8A

  12.  vs temperature

  13. Crowding considerations in the LP + final detector • From the measured thermal neutron rate in the exp. Hall (TN022) one can estimate I 0.5 A in the LP and 5-6 times bigger in the final detector • If this current has to be lower than 1% of the base current (70  A) we have to screen the final detector from thermal neutrons • The corresponding current from low energy photons from the muon radiative decy turns out to be lower than for neutrons: I 04 A in the final detector

  14. Final surptise: last measurements... • Surprise !! after letting few days TB0171 in cold NO EFFECT is seen anymore in this PMT !!! • PMT stabilization? • Temperature offset? • Instrumental error(s) ? • ?? • Check on more PMTs

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