Voltage holding test of full-size mockup bushing for ITER NBI

Tobari, Hiroyuki; Inoue, Takashi; Dairaku, Masayuki; Yamanaka, Haruhiko; Umeda, Naotaka; Taniguchi, Masaki; Kashiwagi, Mieko; Takemoto, Jumpei; Watanabe, Kazuhiro; Sakamoto, Keishi

The high voltage bushing in the ITER NBI has a five-stage structure composed of large bore ceramic rings. The ceramic ring must be 1.56 m in diameter because many conductors are located keeping insulation inside the ceramic ring. However, in conventional technique, the diameter has been limited less than 1 m. The joining technique of the brazing between the large ceramic ring with metal has not been established. Then, new forming method of the large ceramic ring and the brazing technique were developed. As a result, the large ceramic of 1.56 m in diameter was successfully manufactured and the ceramic ring was brazed to Kovar rings with vacuum tightness. To enhance voltage holding capability of the manufactured insulator, stress ring to suppress the breakdown staring from the joining point of the ceramic and metal was also developed. In the high voltage test of the insulator, 240 kV was sustained stably over 1 hour, and the voltage holding capability required in ITER was verified.