Development of movable limiters for JT-60

Japan Atomic Energy Research Institute (JAERI) is planning to make the control devices known as movable limiter for JT-60 (JAERI's Large Tokamak) to suppress skin effect of a plasma current. One pair of limiter bars placed in a large vacuum vessel are required to pull up at a high speed synchronizing with plasma expansion. The actuator system and vacuum seal method have newly been developed. Servo hydraulic system characterized by meter-out flow control is used as drive system and welded bellows with protection mechanism from shock-like operation are used for vacuum seal. In a vacuum vessel, dry bearing is used. Experimental results of operating performance coincided successfully with the calculated values, and vacuum seal device proved its soundness after 10,000 operation of high speed pull-up. Operating ranges of prototype movable limiter are as follows: (1) Mass to be accelerated 235 kg (2) Max. acceleration + 70 G (3) Max. deceleration - 50 G (4) Max. stroke 1,070 mm (5) Max. limiter speed 14.5 m/s. (auth.)