Radiation effects on heated optical fibers

Optical fibers are ubiquitous on today's plasma devices, and will play a major role in future machines. However, radiation causes luminescence and transmission loss in fibers at troubling levels even on today's machines when they operate in DT. We have evaluated these effects and studied the use of elevated operating temperatures to reduce them. Using high-purity UV grade silica-silica fibers at 400 degrees C reduces transmission loss by a factor of at least 100, but has little or no effect on radioluminescence. The radioluminescent spectrum appears to be Cerenkov radiation. The transmission loss spectrum depends on the fiber material and details of the manufacture. The mode structure of transmission loss is mainly simple path length attenuation, with a suggestion of internal reflection degradation. (C) 1997 American Institute of Physics.