Light Collection with Fiber Optics

1. Light Collectionwith Fiber Optics Christopher CrawfordEDM Collaboration Meeting2006-05-25

2. 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)

3. 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

4. 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

5. Light Guide Fiber Optic Bundle Acceptance (internal reflection) TPB TPB FOB

6. 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)

7. 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

8. 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

9. Conclusion & Future Work • Geometry and Material optimizationscan regain 40 photo-electrons • Need to simulate with GuideIt • Integration: which designs are realistic?