Fig. 9-1 In-situ transmission spectrum measurement capsule The stepping motors and micrometers are equipped in the upper part of the capsule to adjust the shift of light axis caused by the thermal expansion of the capsule. A sample changer is also driven by the stepping motor mechanism.

Fig. 9-2 Results of transmission spectrum measurement of windows materials (example) Induced loss was enhanced at the time of reactor shut down even if the irradiation condition was at a lower temperature and lower neutron flux than that during the reactor operation.

Plasma density and temperature in fusion reactors could be measured by a laser light system. A laser light penetrates the transparent windows of the vacuum vessel, is reflected from a mirror and incidentally reflects in the plasma. However, the window materials will be colored and the reflectivity of the mirror materials will be decreased by the exposure to neutron and gamma rays. How does the performance of the windows and the mirror degrade under the irradiation environment of neutron and gamma rays? In order to understand the degradation of these materials during the operation of the fusion reactor, a sealed container which is called in-situ transmission spectrum measurement capsule has been developed for use in the facility of the Japan Materials Testing Reactor (Fig. 9-1). The capsule consists mainly of a two-axis driving system, sample stage, Mo-CCR (Corner Cubic Reflector) and heater. The shift of light axis due to the thermal expansion of capsule can be adjusted by driving the stepping motor mechanism. Another stepping motor mechanism can replace the sample on the sample stage disk for the sequential tests. In these remote-controlled mechanisms, the newly developed radiation-resisted stepping motor and micrometer were used. The induced loss of transmission spectrum for the windows was measured by white light guided by a radiation-resisted optical fiber and Mo-CCR. The results in sapphire and fused silica (KU-quartz) which are candidate window materials are shown in Fig. 9-2. It was found that the induced loss of each specimen increased with increasing neutron flux, and that the induced loss of KU-quartz in the visible wave range was smaller than that of sapphire. The induced loss was enhanced at the time of reactor shut down even if the irradiation condition was at a lower temperature and lower neutron flux than that during the reactor operation. These results contribute to the design of diagnostic components by laser light systems for the ITER. These capsule techniques will be applied to in-situ material testing under neutron irradiation in the reactor core.

Reference E. Ishitsuka et al., Neutron Irradiation Test of Optical Components for Fusion Reactor, 19th Int. Symp. ASTM STP 1366,1176 (2000).

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