Tokamak plasma disruption generates a runaway current carrying enormous amounts of energy that, if not suppressed, can cause severe damage to equipment.

This study aims to investigate the effects of injecting a deuterium-argon/neon gas mixture on a runaway current during plasma disruption.

Based 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 (I_p), ohmic current (I_ohm), runaway current and the ohmic electric field, with the injected deuterium-argon content and ratio during the disruption process were consistently simulated.

Results 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 (I_p) 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 I_p 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.

The pre-disruption plasma current (I_p) is the key factor that influences a runaway current. The larger I_p 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 I_p 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.