Test of Silicon Photomultipliers SiPM at Liquid Nitrogen Temperature

1
Test of Silicon Photomultipliers (SiPM) at Liquid
Nitrogen Temperature

• Yura Efremenko, Vince Cianciolo
• nEDM CalTech Meeting
• 02/14/2007

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SiPM Principle of Operation
Electric field distribution in epitaxial layer
Topology
Real topology is patented and different from it
The pixel size 32x32 µm2
Total number of pixels 576 for 1x1 mm
photodetector
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SiPM
We use standard 42V green sensitive 1_mm SiPM
without any extra modification for low
temperature operation
SiPM was connected to the readout electronics via
following preamplifier
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Experimental Setup
CAMAC DAQ
Control Computer
Signal from SiPM
Optical fiber to SiPM
Cryostat with SiPM
Blue LED
Note the LED and the SiPM wavelengths were not
optimized, but we were looking for a relative
measurement.
Pulse generator
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Protocol

• All equipment was setup and debugged at room
  temperature
• Liquid nitrogen (-1950C) was added into cryostat
• SiPM actually was not inside liquid nitrogen but
  in its vapor
• With remote probe it was verified that SiPM
  temperature is actually at 1950C
• System let alone for extended period of time
• After a day all nitrogen boiled out and
  temperature stat to come back to the room
  temperature.

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Result for Light sensitivity
Horizontal axes on both plots are signal
amplitude in .25 pC. Upper -195OC Lower room
temperature One can see strong improvement in
both light sensitivity and single photon
detection resolution at colder temperatures On
upper plot (-195OC) up to 11 individual photons
can be seen The mean increases twice as much as
the gain, suggesting an increase in the quantum
efficiency of two times.
Liquid Nitrogen
Room temperature
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Transition from Cold to Room Temperature
Horizontal axis time, hours. Upper plot dark
rate Hz Single photon noise rate 10 kHz. Lower
plot signal charge, in 0.25 pC. One can clearly
see that noise was lower and gain was higher at
low temperature. Between 15 and 23 hour, SiPM
was illuminated by ambient light to test its
recovery back to single photon regime after
exposure to strong light. Its performed as
expected
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One possibility for nEDM Light Readout w/SiPMs
Top View
Front View
Clear fibers out to SiPMs
WLS fibers
Tyvek coating
Inside of mst. cell
WLS fibers
TPB impregnated acrylic
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Estimate of photons

• Initially 8350 prompt EUV photons from neutron
  capture.
• 5470/250 KeV ß (764KeV/250 KeV) 50 1
• dTPB conversion efficiency (in matrix) 30
• Blue-to-Green conversion efficiency in WLS fibers
  35
• Assume 8 of area covered w/ WLS fibers, 88
  reflectivity for TYVEK
• 8 is four 1mm fiber loops/side (32
  channels/cell)
• Could gain by adding more fiber coverage with
  resulting increase in of channels.
• Capture inside WLS fibers 7
• Readout both ends.
• Attenuation in WLS fibers 85
• 3m attenuation length, assume 25 cm average
  length few loss at clear/WLS fiber joint.
• Sensor efficiency 70
• Guesstimate based on room temperature quantum
  efficiency of 35 and observed x2 increase at LN2
  temperature.
• Total photons/event 37
• Paul H. suggested the possibility of multi-clad
  fibers coated w/ TPB inside the acrylic.
• Could gain x4 in TPB efficiency.
• Activation issues?

Realistic
Pessimistic
Optimistic
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Other Advantages

• Very small power consumption
• Small service penetration requirements
• Exactly how much depends on location of
  preamplifiers.
• Not expected to be affected by magnetic fields.
• Should be tested.

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Conclusion To Do

• SiPM performed extremely well ant liquid nitrogen
  temperature.
• According to all tested parameters its
  performance did not show any degradation but
  rather improvement.
• Future tests at even lower temperatures are
  possible.
• Assembling a setup to make absolute measurement
  of quantum efficiency.