Nuclear radiation effects in fused SiO2 lightguides

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Abstract
High purity fused silica fibers are widely used in controlled fusion research to conduct visible light (down to about 4000 Å) away from the hostile environment of the tokamak. These fibers are not totally radiation immune, however. We see both luminescence and loss of transmission induced by radiation at the present levels of D–D fusion yields on Tokamak Fusion Test Reactor (TFTR). The luminescence shows spectral structure and is brightest near the widely used Hα–Dα wavelength of 6562 Å. The induced opacity has both transient (time scale of seconds) and permanent components. Extrapolation to D–T plasmas, which are planned for TFTR, yields levels of both luminescence and opacity which range from annoying to fatal if current practices are continued.