Conceptual design of the MGI system for JT-60SA

Disruption mitigation is of high priority for future tokamaks like ITER and DEMO. Massive gas injection (MGI) has proven to be an effective method in medium size machines and will likely be part of future disruption mitigation systems. For further research, the large superconducting tokamak JT-60SA will be equipped with a MGI system as an experimental equipment. This system will consist of two in-vessel MGI valves, which are mounted in opposite segments of the machine, vacuum feed throughs, a gas preparation system and an industrial PLC for control. The MGI valves are a scaled version of the spring-driven valve used in ADSEX Upgrade with an internal gas reservoir of 815 cm³, a maximum mitigation gas pressure of 6.5 MPa, a closing pressure of about 2 MPa, a nozzle diameter of 28 mm and an opening time below 2 ms. CFD simulations with common gas mixtures indicate a peak flow rate of 3.8 kg/s after 1.6 ms. The valve has a size of 140 mm x 110 mm x 292 mm. The gas preparation system allows easy and reproducible mixing of two gases by using an electronic pressure controller.