Yasuhiko Miyo

Tritium Distribution on First Wall Carbon Tiles in JT-60U

Abstract T retention and its depth profile in the graphite tiles used for first wall of JT-60U have been measured by a tritium imaging plate technique and a full combustion method. T was found only limited depth beneath the plasma facing surface and little in both the surface region shallow than 1 μm and in bulk more than 1mm in depth. Although most of T produced by DD reactions are thermalized and neutralized in plasma and impinge on the plasma facing surface and penetrate into the inner surface, they are isotopically replaced by subsequently incoming D. Only some of high energy T escaping from plasma are directly implanted beneath the surface and retained escaping from the isotopic replacement until attainment of a saturation concentration.

Hydrogen Isotopes Retention in Gaps at the JT-60U First Wall Tiles

Retentions of Hydrogen (H) and deuterium (D) in the side surfaces (gaps between tiles) of the carbon tiles used as first wall in JT-60U were measured by the thermal desorption spectroscopy. In the gaps, the H and D retention were dominated in carbon deposited layer. The gap retention was less than that of the eroded plasma facing surface, where the retention was saturated, and linearly increased with exposure time. Overall retention rate in the gaps of the first wall tiles was determined to be 4.0 × 1019 H+D/s, and was comparable or larger than those in the re-deposited layers on the plasma facing surfaces and in the shadowed areas in the divertor region.

Tritium Retention in First Wall Tile Gaps of JT-60U

Abstract Tritium (T) retentions in tile gaps (side surfaces) of the first wall of JT-60U were measured by a tritium imaging plate technique (TIPT). For all first wall tiles measured here, the T retention decreased from the front (entrance) to the bottom of the side surfaces showing superposing two exponential decays, which were already observed in the divertor region. Heavier erosion on the plasma-facing surface resulted in higher T retention in the front-side surfaces in the vicinity of the plasma-facing surface. In addition, wider gap width also resulted in higher T retention in the bottom side surfaces. Using the TIPT results, overall T retention in the side surfaces of the whole first wall was estimated to be ~6 × 1017 T atoms, which was only one-tenth of total T retention in the plasma-facing surface of the first wall in JT-60U.

Gas and Pellet Injection Systems for JT-60 and JT-60U

Designs and operations of the gas system and pellet injection systems for JT-60 and JT-60U are described. A gas injection valve that is a key component of the gas injection system was developed using a multilayer piezoelectric element. The maximum flow rate of this system is 43.3 Pa⋅m3/s. The valve has mechanism for adjustment at atmospheric side meaning that a repair and an adjustment can be conducted without ventilation inside a vacuum vessel. It was confirmed that the effect of magnetic field and temperature change on the valves in the JT-60U environment was negligible. In JT-60U, two systems of pellet injector – a pneumatic drive and a centrifugal one – were developed. The pneumatic type attained a pellet velocity of 2.3 km/s, which was the world record at the time in 1988. On the other hand, the centrifugal one was developed in 1998. This injector can eject trains of up to 40 cubic (2.1 mm3) pellets at frequencies of 1 to 10 Hz and speed of 0.1 to 1.0 km/s. A guide tube for a magnetic high field side injection (HFS) (top) was also developed in 1999. The pellet injection experiment with the HFS system started in 2000. In addition, another guide tube for HFS(mid) injection was newly developed and installed in March 2001. These systems are working well.