Mechanical design of a Fast Shutter for the ITER disruption mitigation system

ITER is a large-scale experimental nuclear fusion reactor currently under construction. To protect the first wall components of the machine against damages due to a plasma disruption event, ITER needs a Disruption Mitigation System (DMS). The ITER DMS is based on the Shattered Pellet Injector (SPI) technology. One of the issues with SPI injection is that the propellant gas may overtake the pellet and start plasma edge cooling before material deposition by pellet fragments takes place. Edge cooling may increase runaway electron generation, therefore should be avoided. To address this problem, the ITER Organization has launched a project to develop Fast Shutter which serves an important role by closing the orifice right after the pellet passed the component. The shutter must be closed within a few milliseconds to block enough gas according to the simulations. It will be installed close to the torus, where the equipment will be exposed to a high magnetic field, and neutron irradiation. Due to limited accessibility for maintenance, the shutter must operate thousands of cycles. This paper describes the detailed design of the shutter prototype and its present capabilities. The proposed concept addresses the issue of high dynamic loads resulting from the fast-closing time of the device, which can cause fatigue due to cyclic loading. The unique environmental conditions necessitate the use of special actuators and materials. The design space available for the implementation of the concept is relatively small, which requires the optimization of the arrangement of device components to minimize the overall loads and maximize the device's efficiency.