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Light Collection with Fiber Optics. Christopher Crawford EDM Collaboration Meeting 2006-05-25. Review. Steve Williamson presentation (2004-12) Simulations with GuideIt MC code Downstream guide (behind beam stop) Single-ended edge guide 0.3 K to 300 K Transition guide

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Light collection with fiber optics

Light Collectionwith Fiber Optics

Christopher CrawfordEDM Collaboration Meeting2006-05-25


Review
Review

  • Steve Williamson presentation (2004-12)

    • Simulations with GuideIt MC code

    • Downstream guide (behind beam stop)

    • Single-ended edge guide

    • 0.3 K to 300 K Transition guide

  • NIST Magnetic UCN trap

    • Also simulated with GuideIt

    • Measured efficiency of similar geometry

    • 360 keV (source) /16 eV (UV) * 35% (prompt UV)* 0.1 (PMT eff.) * epsilon = 6 p.e. (measured)

    • epsilon = 0.8 % (acceptance * attenuation)


Problem
Problem

  • Efficiency too low:

    • 3He + n -> p + t + 700 keV (12 p.e.)

    • Need 40 p.e. for optimal PID

  • Charge:

    • Investigate Fiber Optic Bundles (FOB)

    • Collect light from top/bottom, not end

    • Advantage: larger surface area


Material properties

Acrylic Light Guide

d = 150-500 cm (atten)

n = 1.508 (index refr.)

thc = 41.5 deg

Fiber Optic Bundle

`Toray` 3 mm O.D.

d ~ 21 m (0.2 dB/m)

Core: no = 1.492

Clad: nc = 1.408

10 micron thick

N.A. = 0.5

Packing fraction = 90%

Sample shipped to LANL

Material Properties


Acceptance internal reflection

Light Guide

Fiber Optic Bundle

Acceptance (internal reflection)

TPB

TPB

FOB


Enhancements
Enhancements

  • Capture photons back-propagating through the 3He cell

    • Light guide inefficient for this angle

    • Not quite a factor of 2

  • Optical fibers without cladding

    • Still total internal reflection

      NA = 1.10, theta = 42.7 deg, Omega=2.016

      A = 0.16 = 16 x (guide)


Enhancements1
Enhancements

  • Increase distance from TBP, and

  • Insert fibers at optimal angle

    • Look at greater density of TBP from ends

    • Ideal: semi-circle interface, A=0.5

ideal

TPB

realistic

FOB


Enhancements2
Enhancements

  • Use larger n guide

    • Polystyrene (TPD): n=1.55-1.59

    • Larger n guide refracts to less divergence

  • Use tapered light guide

    • Increase effective critical angle

    • Less wall bounces


Conclusion future work
Conclusion & Future Work

  • Geometry and Material optimizationscan regain 40 photo-electrons

  • Need to simulate with GuideIt

  • Integration: which designs are realistic?


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