LUMINESCENCE AND TRANSMISSION MEASUREMENTS ON FIBERS EXPOSED TO HIGH NEUTRON FLUXES

Fiber-based diagnostic systems suffer from induced luminescence and transmission losses due to neutron and γ radiation from high-power D-D and D-T discharges. Whereas the luminescence follows the neutron rate, the transmission loss increases monotonically during a shot and decays slowly after the discharge. To study these effects we are using dedicated fiber coils (increasing the exposed length) which are positioned close to the discharge vessel (increasing the neutron flux) and close to neutron detectors. The fibers studied are typical for diagnostics on TFTR. One fiber is of the same type used for the JET/TFTR heated fiber study. We measure spectrally selected luminescence and transmission with a light emitting diode based, modulated three-phase exciter system. We have measured substantial transmission losses during D-T shots which reduce the test signals and the radioluminescence. The transmission losses recover only partially; we will show first long-term measurements of the loss recovery. A simple model is presented which allows the derivation of values for luminescence source strength per length unit and neutron flux even if the luminescence is reduced by the induced transmission loss. © 1995 American Institute of Physics.