Clean-up of graphite first walls in JT-60

Abstract

During the venting period from April to May 1987 about a half of TiC-coated molybdenum and Inconel 625 first walls were removed and graphite first walls were installed. The overall surface area and the weight of the graphite tiles are 200 m 2 and 3500 kg, respectively. Two kinds of isotropic graphite (Ibiden ETP-10 and Hitachi-Chemical HCB-18S) were used. Special attention was paid to the contamination of the graphite first walls during the courses of fabrication and installation. Main discharge were tried after 7 d conditioning, which included 3 d bakeout at the temperature of 300°C, 18 h glow discharge cleaning and 36 h Taylor-type discharge cleaning keeping the vessel temperature around 280°C. A 0.5 MA stable plasma was successfully attained at the 6th shot and a very rapid start-up of the discharge conditioning with plasma current up to 1 MA was achieved with 14 shots. An ultimate pressure of 6.4 × 10 −7 Pa was obtained with the vessel temperature at RT and the residual gases were water, carbon oxide and carbon hydride.