Gain and Quantum Efficiency of a Cold Photomultiplier

Hans-Otto MeyerIndiana University10/7/06

run a Hamamatsu R7725 @ 4 K

determine minimum heat load

measure quantum efficiency and gain vs T

… and vs frequency

The Plan

cold warm

R7725Monitor PM

thermometer

base part 1

opt. fiber

base part 2

light pulser

light splitter

Enclosure(evacuated, submersed in cryo-liquid)

existing at this time (9/27/06)

warmPM under testBurle 8850

Monitor(8575)

base

opt. fiber

light pulser

light splitter

data acquisition

Light source

pulse width: ~10 ns

λ = 467 nmLED (LITEON LTST-C150)

Splitter(imperfect splice in clear epoxy)

mounted LED

n-channelMosfet

setup

ne = 3.6 ne = 2.0

ne = 1.1 ne = 0.52

ne = 0.034ne = 0.10

red curve:

peak index

21

21

2

)(

1 2

),()(

k

xkxx

k

e ek

nkpxG

xx ,, 11 determined once and for all

ne (avg. number of photoelectrons) from

fitQuantum efficiency: from ne

PM gain: from peak locations

measure quantum efficiency

ne= 1.055gain ≡ 1.0

ne= 1.053gain ≡ 1.6

ne= 1.055gain ≡ 2.5

measure gain

changing PM HV:

gain changes, but ne stays the same

photoelectrons vs monitor signal

0.01

0.1

1

10

10 100 1000 10000

monitor centroid (channels)

ave

rag

e n

um

be

r o

f p

ho

toe

lect

ron

s

monitor

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

+HV signal

cold

warmlong leads

R7725 split base

How is performance affected?Ho to fix it?

Radiant heat transfer between concentric cylinders

length of cylinders L 0.2m Stephan Boiltzmann 5.67108

W

m2

K4

inner radius r1 0.025m

outer radius r2 0.035m

inner emissivity 1 0.8 inner temperature: varying T1 = T

outer emissivity 2 0.8 mass of inner cylinder (steel) Ms 0.3kg

outer temperature T2 4K

1 10 100 1 1030.01

0.1

1

10

100

1 103

cooling rate

T (K)

cool

ing

rate

(K

/hou

r)

1 10 100 1 1030

50

100

150

time for cool-down

final temperature (K)

tota

l tim

e (h

ours

)

T2

T

cooling

Project is on hold