Test of Silicon Photomultipliers (SiPM) at Liquid Nitrogen Temperature

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

SiPM – Principle of Operation

Topology The pixel size – 32x32 μm

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Total number of pixels – 576 for 1x1 mm photodetector Real topology is patented and different from it Electric field distribution in epitaxial layer

SiPM

We use standard 42V green sensitive 1_mm SiPM without any extra modification for low temperature operation

1mm

SiPM was connected to the readout electronics via following preamplifier

SiPM

Control Computer

Experimental Setup

CAMAC DAQ Pulse generator Optical fiber to SiPM Signal from SiPM Blue LED

Note: the LED and the SiPM wavelengths were not optimized, but we were looking for a relative measurement.

Cryostat with SiPM

Protocol •

All equipment was setup and debugged at room temperature

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Liquid nitrogen (-195 0 C) was added into cryostat

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SiPM actually was not inside liquid nitrogen but in its vapor

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With remote probe it was verified that SiPM temperature is actually at –195 0 C

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System let alone for extended period of time

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After a day all nitrogen boiled out and temperature stat to come back to the room temperature.

Result for Light sensitivity Gain increases by x1.8

Horizontal axes on both plots are signal amplitude in .25 pC. Upper: -195 O C Lower: room temperature

Liquid Nitrogen Mean increases by x3.6

One can see strong improvement in both light sensitivity and single photon detection resolution at colder temperatures On upper plot (-195 O C) up to 11 individual photons can be seen

Room temperature

The mean increases twice as much as the gain, suggesting an increase in the quantum efficiency of two times.

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

One possibility for nEDM Light Readout w/SiPMs

Front View WLS fibers Top View Clear fibers out to SiPMs Tyvek coating Inside of mst. cell WLS fibers TPB impregnated acrylic

Estimate of #photons

• Initially ~ 8350 prompt EUV photons from neutron capture.

– 5470/250 KeV β (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 – Could gain ~ x4 in TPB efficiency.

– Activation issues?

Realistic Pessimistic [1] D.N. McKinsey et al., NIM A516 (2004) 475.

Optimistic

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.

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.