Light Transport and Detection with VLPCs

D. Dutta TUNL/ Duke University

MEP group

Current Cell Design

Current Design for Light Transport

C. R. Brome et al., PRC 63, 055502 (2001)

Visible Light Photon Counters

VLPC's are arsenic doped silicon diodes,designed to convert single photons in to many thousands of electrons with high quantum efficiency

Detects single photons Operate at a few degrees Kelvin Quantum efficiency ~80% Insensitive to magnetic fields High gain ~40 000 electrons per converted photon

Visible Light Photon Counters

Excellent individual photoelectron resolution SVX Readout (ADC Counts) of Cassette A (T=8.2K, V=7V)

0

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40 60 80 100 120 140 160 180 200Integrated Charge

Low gain dispersion ~0.13 p.e.

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1400

0 10 20 30 40 50 60 70 80

Gain (in Thousands)

Fre

qu

en

cy

Visible Light Photon Counters

Ideal operating temperature ~ 6.5 K

S. Takeuchi et al., Appl. Phys. Lett, 74, 1063 (1999)

High gain ~ 20,000- 60,000

VLPC Applications

Extensively used in Scintillating Fiber Trackers @ Fermilab

Fermilab has 10+ yrs of experience and expertise

VLPC Applications

Alternative Cell Design

d

Studies by nEDM Collaborators

Wavelength shifting fiber based detector was tested by the Doyle group for their neutron traps.

D. N. McKinsey et al., NIM A 516,475 (2004)

QRCeSYFN Sll att /1/)1(

detector of eff. quantum

coating ofty reflectivi

fiber oflength

fiberfor eff. conv.

fiberby covered surface offraction

eff. converv. TPB

yieldphoton EUV

Q

R

l

C

S

F

Y

Studies by nEDM Collaborators

D. N. McKinsey et al., NIM A 516,475 (2004)

But acrylic tube based light transport detected ~5.5 p.e. in the neutron lifetime measurement cell , due to more complicated & less efficient optics. => optics is 3% efficient not 31%

P. R. Huffman et al., Nature 403, 62 (2000).C. R. Brome et al., PRC 63, 055502 (2001).

Comparison with Current Design

QRCeYFTN Sll

Acrylicatt /1/

detector of eff. quantum

coating ofty reflectivi

fiber oflength

fiberfor eff. conv.

Acrylic of eff.sport light tran

fiberby covered surface offraction

eff. converv. TPB

yieldphoton EUV

Q

R

l

C

T

S

F

Y

Acrylic

old new

(1-S) = 0.88 S = 0.8

2.4 m 8.5 m

~ 1.1

~ 0.17

0.19 0.85 ~ 4.5 ~ 4

0.25 0.88 ~ 3.5

-- 0.7 ~ 0.7 ~ 0.4

net

Optics 0.4 0.8 ~ 2.0

Expected Performance

Acrylic tube+ PMT Acrylic tube+ WLSfiber+ VLPC

# of photonscollected in cryo cell

Efficiency of transport to detector

Quantum Eff.

# of photo-electrons

N 0.4* N /4

3% 80%

20% 80%

0.064*N 0.006*N

Relevant Studies by nEDM Collaborators

The Doyle group also attempted to test wavelength shifting fiber based detector with VLPCs instead of PMTs.

J. S. Butterworth et al., Private Communication

“Failed to get the pre-amp board working, it was too noisy.” - James Butterworth

VLPC, wavelength shifting fiber, pre-amplifier board and biasing circuit borrowed from Fermilab.

New Readout MethodUse a ultra low-noise amplification scheme developed for single photon counting experiments

J. Kim et al., Appl. Phys. Lett, 70, 2852 (1997) S. Takeuchi et al., Appl. Phys. Lett, 74, 1063 (1999)

Pros & Cons

• Shorter pathlength from cell to detector

• No breaks in the light guide.

• lower backgrounds

• lower noise

• Discrimination of gammas with afterpulses may not be feasible

Cost Estimates

• VLPC + Readout: $3000/channel x 16 channels = $48,000

• Temperature controller+ Fiber + Misc: $2,000

Cost per cell : $50,000 Net cost: $100,000

Test Setup at Duke

Status of the Duke Project

Dewar, dTPB coated acrylic, Am source, WLS fiber, VLPC chips have been obtained.

The low noise readout circuit is being built. Special order cold amplifier from NFE Japan has arrived.

Mary Kidd ( 1st yr Grad student) worked on designing parts of the Duke test setup last summer. Alan Ye will take over the project as the he-3 relaxation study at Duke wraps up.

A trip to Fermilab, to learn on their test setup and to get WLS fiberspliced to clear fiber, is being planned ( delayed due to broken cryostat at Fermilab, waiting for repairs.)

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Fermilab Test Setup

10 60s2 ms s

VLPC biasCryostat

PreamplifierBoard

Preamppower

HP 8112APulse Generator

LED

VLPC

Delay

Gate

input

LeCroy2249A

Transformer

PC

ITC4

Background

SignalHP 8112APulse Generator

LED zz

Conclusions

10 60s2 ms s

• WLS Fiber + VLPC based cell maybe more efficient in transporting and detecting scintillation light.

• New design needs to be tested and must be proven

• Tests under way at Duke should help decide.