1. Light Collection with Fiber Optics Christopher Crawford EDM Collaboration Meeting 2006-05-25

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: – 3 He + 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. Material Properties Acrylic Light Guide d = 150-500 cm (atten) n = 1.508 (index refr.) th c = 41.5 deg Fiber Optic Bundle `Toray` 3 mm O.D. d ~ 21 m (0.2 dB/m) Core: n o = 1.492 Clad: n c = 1.408 10 micron thick N.A. = 0.5 Packing fraction = 90% Sample shipped to LANL

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

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 TPB FOB realisticideal

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 optimizations can regain 40 photo-electrons Need to simulate with GuideIt Integration: which designs are realistic?