Tritium (T) and deuterium (D) are used as fuel for a nuclear fusion reactor. Most atoms of these hydrogen (H) isotopes remain in the inner wall of the vacuum vessel. It is, therefore, important to measure the remaining distribution of H isotopes, in particular the radioisotope (T), in the wall from the viewpoint of maintenance safety of a future reactor. Although measurement of the T remaining in the wall needed much time in the past, a relatively short measurement time for wide areas of T distribution recently became possible by applying an imaging plate technique.
This T detector is composed of an imaging plate (coated with a Photo-Simulated Luminescence (PSL) substance) and a laser-based imaging reader. When the imaging plate coated with the PSL material is exposed to radiation, quasi-stable color centers are formed in the PSL substance. By scanning the PSL film with the laser beam, short wavelength light is emitted from the color centers in proportion to the distribution density. Two-dimensional intensity distribution of the incident radiation can be obtained from the light intensity distribution.
In JT-60, T distribution in the carbon-based first wall surface (within several microns) was measured using this detector to study the T behavior produced by D nuclear reaction. Fig. 2-15 shows a comparison of the results of the T measurement and the orbit loss simulation of high-energy T ions in plasma. Both results for T distribution have good agreement. It was, therefore, found that the T retention reflects the incident distribution of the T ions lost from plasma.
To clarify the plasma-wall interaction, we will measure the T distribution further over a wider area.
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