Light Transport and Detection with VLPCs

Dipangkar Dutta TUNL/ Duke University

MEP group

Current Conceptual Design

Light Transport to PMTs

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)

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Low gain dispersion ~0.13 p.e.

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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

Ex TUNL, borrowed couple of bare VLPC chips from him

Asst. Prof. at Duke EE dept, (developed new cheap cold amplifiers for VLPCs)

Alternative Conceptual Design

d

The Issues

• Shorter pathlength from cell to detector

• No breaks in the light guide.

• lower backgrounds

• Light collected in the cell could be smaller

• No previous experience, unlike the light guides.

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)

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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 Method

Use 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)

Test Setup at Duke

Summer 2005 by REU student Amber Nelson

Test Cells at Duke

Test Cells at Duke

New Readout Method

WarmAmp

The Early Tests

• No signal detected (not even dark counts) • Excessive noise.

After several unsuccessful attempts, we loaned the VLPC chips to Prof. Jungsang Kim of the Duke EE Department to test them in his apparatus.

The test was simplified to detect just the signal from dark counts

Do the VLPC chips still work after so many years?

Jungsang Kim’s Apparatus

To Vacuum pumpTo warmAmplifier

Cold Amplifier

VLPC

Signal was seenimmediately,

VLPC chips werenot broken!!

Bare-bones Test Setup

Fall 2005 –Spring 2006 Duke UndergradAlvaro Chavarria

Bare-bones Test Setup

A spectrumanalyzer was used to determine allsources of noise

A low pass filters was added toall inputs andoutputs

First Signal

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Observed in Prof. Kim’s Lab

First Signal (Repeat)

Repeated in our lab

The New Setup (cell test)

May 2006

The New Setup (cell test)

May 2006

Once again in thisnew setup noise is toohigh to even see thedark counts.

The Next Step

May 2006

Replace G10 tube withmetal tube and repeat

The Final Steps

Re-establish the dark count signal in the new setup. Look for changes in the signal when an Am241

source is lowered into the dTPB coated cell.

Tests to be performed over the next few weeks.

Vince and Yuri will come up to Duke to test their silicon photo multipliers coupled to the fiber cell.