Impurity control by boronization and optimization of the wall temperature in JT-60U
Tomohide Nakano, Satoru Higashijima, Hirotaka Kubo, Tatsuo Sugie, Nobuyuki Asakura, Hidenobu Takenaga, Kiyoshi Itami
Japan Atomic Energy Research Institute, Ibaraki, 311-0193, Japan
Abstract.
In JT-60U, boronization using deuterated decaborane has been applied to suppress oxygen production. Boronization decreased the oxygen content in the core plasma from ~ 3% to ~ 0.5%. The oxygen content of ~ 0.5% was kept by additional boronization about every 100 shots. By lowering the vessel temperature from 540 K to 420 K, chemical sputtering yield decreased by ~ 40% at the carbon divertor plates. For hydrogen plasmas, the carbon content reduced from 3.1% to 1.8% in L-mode discharges with NB heating power of 13 MW, and from 2.4% to 1.7% in reversed shear discharges. For deuterium plasmas, however, the carbon content did not depend on the vessel temperature. The different dependence of the carbon content on the vessel temperature is considered to be due to isotopic difference between chemical and physical sputtering yield. The effects of boronization and the vessel temperature will be discussed based on correlation between impurity content and impurity influx from the divertor plates and the first walls.