Screening Tests of Isotropic Graphites and C/C Composites for JT-60U Plasma Facing Components

Abstract

Physical and mechanical properties of newly developed carbon/carbon (C/C) com-posites and isotropic graphites have been measured for application to the first wall and divertor plate of JAERI Tokamak-60 Upgrade (JT-60U). The divertor plate of JT-60U is subjected to high heat flux of up to 20 MW/m2 during normal operations and to large thermal shock during disruptions. The surface temperature of the divertor plate should be lowered enough to prevent unacceptable carbon influx due to sublimation. The evaluation of these plasma facing component materials has been made mainly from thermal conductivity, thermal shock resistance and mechanical strength points of view. Outgassing properties and erosion characteristics against high heat flux are also considered in selecting the materials. It is found from these tests that a few kinds of 2-D felt type C/C composites have large thermal shock resistances and superior thermal conductivity in the range of 300-400 W·m-1·K-1 at room temperature which satisfies the JT-60U design requirement of 300 W·m-1·K-1. In addition, the investigated isotropic graphites also exhibit; improved thermal conductivity in the range of 150-180 W·m-1·K-1 at room temperature. Con-sequently, 2-D felt type C/C composites with superior thermal conductivity have been selected for the divertor plate. As for the first wall, two grades of isotropic graphites with relatively high thermal conductivity have also been selected as well as one which was used in the JT-60 operation.