1. Light Transport and Detection with VLPCs D. Dutta TUNL/ Duke University MEP group

2. Current Cell Design

3. Current Design for Light Transport C. R. Brome et al., PRC 63, 055502 (2001)

4. 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

5. Visible Light Photon Counters Excellent individual photoelectron resolution Integrated Charge Low gain dispersion ~0.13 p.e.

6. 0 200 400 600 800 1000 1200 1400 01020304050607080 Gain (in Thousands) Frequency   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

7. VLPC Applications Extensively used in Scintillating Fiber Trackers @ Fermilab Fermilab has 10+ yrs of experience and expertise

8. VLPC Applications

9. Alternative Cell Design d

10. 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)

11. 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).

12. Comparison with Current Design oldnew (1-S) = 0.88 S = 0.8 2.4 m8.5 m ~ 1.1 ~ 0.17 0.190.85 ~ 4.5 ~ 4 0.250.88 ~ 3.5 --0.7~ 0.7 ~ 0.4 net Optics 0.40.8~ 2.0

13. Expected Performance Acrylic tube+ PMT Acrylic tube+ WLSfiber + VLPC # of photons collected in cryo cell Efficiency of transport to detector Quantum Eff. # of photo- electrons N0.4* N /4 3%80% 20% 80% 0.064*N 0.006*N

14. 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.

15. 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)

16. 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

17. 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

18. Test Setup at Duke

19. 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 ( 1 st 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 fiber spliced to clear fiber, is being planned ( delayed due to broken cryostat at Fermilab, waiting for repairs.) 241

20. Fermilab Test Setup 1060  s 2 ms  s

21. Conclusions 1060  s 2 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.