1. Gain and Quantum Efficiency of a Cold Photomultiplier Hans-Otto Meyer Indiana University 10/7/06  run a Hamamatsu R7725 @ 4 K  determine minimum heat load  measure quantum efficiency and gain vs T  … and vs frequency

2. The Plan cold warm R7725 Monitor PM thermometer base part 1 opt. fiber base part 2 light pulser light splitter Enclosure (evacuated, submersed in cryo-liquid)

3. existing at this time (9/27/06) warm PM under test Burle 8850 Monitor (8575) base opt. fiber light pulser light splitter data acquisition

4. Light source pulse width: ~10 ns λ = 467 nmLED (LITEON LTST-C150) Splitter (imperfect splice in clear epoxy) mounted LED n-channel Mosfet

5. setup

6. n e = 3.6 n e = 2.0n e = 1.1 n e = 0.52 n e = 0.034 n e = 0.10 red curve: peak index determined once and for all n e (avg. number of photoelectrons) from fit Quantum efficiency: from n e PM gain: from peak locations measure quantum efficiency

7. n e = 1.055 gain ≡ 1.0 n e = 1.053 gain ≡ 1.6 n e = 1.055 gain ≡ 2.5 measure gain changing PM HV: gain changes, but n e stays the same

8. monitor The monitor signal is proportional to the light emitted from the splitter

9. +HV signal cold warm long leads R7725 split base How is performance affected? Ho to fix it?

10. T2T2 T cooling

11.  Mechanical sample is available (will die during a cooling rate test)  Unmodified tube just arrived (will be tested while cooling: fails when & how?)  Modified tube on order Others: Rossella et al (ICARUS) McKinsey et al

12. Project is on hold