The design and application of the movable limiter in EAST

There are two movable limiters that have been installed on EAST. The movable limiter consists of three parts that are blade, support components and drive components. The blade which consists of heat sink and graphite tiles has to face plasma during plasma discharge. The support components consist of a long shaft and a movable plate. The drive components consists of a screw shaft, a step motor, four guide shafts and two support plates. There is an extra support which has fit in Tokamak and a frame on the outside of the flange. The specific shape of the blade has been optimized so that the graphite tiles on the blade can withstand max 5 MW/m^2 heat load with two long cooling channels. The long shaft of the transfer components connect with blade to make it can move along the axis of the limiter. The movable blade could adjust a wide variety of plasma major and minor diameters. The drive components provide motion from step motor which can be remote controlled in the control room far away from the scene. The rotation is translated to slide motion by a screw shaft. The screw shaft can push the slide which connected with the long shaft to at last move the blade. To introduce the motion from outside to the vacuum vessel, the limiter has a long bellow and special structure as dynamical seal. This seal structure proved very reliable. The remote control system has been also equipped the distance sensor to provide the information of the position of the limiter. The control system is based on PC so it can be easily operated. The two movable limiters have been installed on the EAST. During past twice discharges, the movable limiter proved to be a useful tool for EAST to control the plasma boundary.