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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. - PowerPoint PPT Presentation
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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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40 60 80 100 120 140 160 180 200Integrated Charge
Low gain dispersion ~0.13 p.e.
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0 10 20 30 40 50 60 70 80
Gain (in Thousands)
Fre
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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)
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
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
0.0
5.0
10.0
15.0
-5.0
Volt
ag
e (
mV
)
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.