Numerical investigation of Tokamak runaway current suppression by using massive deuterium-argon/neon gas mixture injection

BackgroundTokamak plasma disruption generates a runaway current carrying enormous amounts of energy that, if not suppressed, can cause severe damage to equipment.PurposeThis study aims to investigate the effects of injecting a deuterium-argon/neon gas mixture on a runaway current during plasma disruption.MethodsBased on the high plasma current discharge conditions of the HL-2M tokamak device in China, numerical simulations were conducted using a fluid model in the DREAM code. Variations of plasma parameters, such as plasma current (Ip), ohmic current (Iohm), runaway current and the ohmic electric field, with the injected deuterium-argon content and ratio during the disruption process were consistently simulated.ResultsResults show that injecting a deuterium-argon/neon gas mixture suppresses the eventual formation of a platform runaway current, and an optimal content and ratio of the deuterium-argon/neon gas mixture are existed for effective runaway current suppression. Within the range of the pre-disruption plasma current (Ip) discussed in this study, the amounts of neon/argon and deuterium in the gas mixture should be 0.50%~0.70% and 1020~1021 m-3, On fusion-reactor-scale tokamak devices with Ip as high as 10 MA, the amount of the injected gas mixture must reach 1022 m-3, which cannot be achieved under the current massive gas injection (MGI) technique.ConclusionsThe pre-disruption plasma current (Ip) is the key factor that influences a runaway current. The larger Ip is, the larger is the runaway current that is formed and more amount of the gas mixture must be injected. On fusion-reactor-scale tokamak devices with Ip as high as 10 MA, the amount of the injected gas mixture must reach 1022 m-3, which cannot be achieved under the current massive gas injection technique. Injecting a deuterium-argon/neon gas mixture through a shattered pellet would be a more viable approach.