In this month, conditioning operation was carried out as an initial operation stage after one year maintenance period. Boron coating of the first wall was also performed.
(1) Conditioning operation
Wall conditioning was carried out by the combination of the Taylor discharge cleaning (TDC) and the glow discharge cleaning (GDC) before the beginning of tokamak operation. Conditioning of NBI port, ECRF system and first wall were carried out after the tokamak operation became possible. The wall temperature was kept at 260C to enhance degassing in this month. The pulse length of tangential NBs, #7 to #10, was extended up to 19-21 s. Modification of power supply for #2, 3, 6 in this year enables us to inject the NBs for more than 10s in addition to #14. Thus, the pulse length of 4 perpendicular NBs (#2, 3, 6 and 14) were extended up to 17 s (maximum unit of #14) limited by shine-through interlock. Maximum pulse length of the other perpendicular NBs (#3, 4 and 12) was extended to the rated value of 10s. Long-pulse injection of ECRF was successful, and the pulse length was extended to as long as 30 s, which is the longest value ever achieved in JT-60U. The H/D ratio, evaluated by the ratio of Hα to Dα at the plasma start up (t = 0.3 s), decreased smoothly to 0.2. The amount of oxygen content, which was evaluated by the ratio of OVIII to CVI line-intensities, also decreased steadily and the value reached low level enough to perform Boron coating.
(2) Boron coating of the first wall
After three weeks of the conditioning operation, boron coating of the first wall was performed by GDC with the He gas and the decaborane (B10D14) vapor. A total amount of 50 g decaborane was used during ~46 hours GDC.