Speaker
Description
High-energy relativistic runaway electron (RE) beams emerge during plasma disruptions in tokamaks through avalanche multiplication processes. This phenomenon arises from the synergistic interplay of Dreicer acceleration and knock-on collisions, potentially jeopardizing plasma-facing components through localized energy deposition exceeding 10 MJ/m². Advanced MHD simulations have revealed that in post-thermal-quench RE scenarios with enhanced plasma resistivity (η > 10⁻³ Ω·m), the resistive hose modes, a kink-type instability characteristic of self-pinched relativistic electron beams, exhibit growth rates exceeding those of resistive tearing modes (TM) by up to two orders of magnitude at most. This disparity in instability development timescales poses significant challenges for beam confinement mitigation strategies in ITER-relevant disruption conditions. Moreover, the resistive hose mode may nonlinearly couple with other MHD modes, largely complicating the RE mitigating strategies. Thus, it is essential to investigate the nonlinear dynamics of resistive hose modes for runaway electron beams in post-disruption tokamak plasmas for its better mitigation. In this work, the macroscale effects of REs in tokamaks are treated as a separate cold beam-like fluid species in extended MHD simulations. The RE beam is considered as a source of resistance-free current density whose direction depends on the time evolving magnetic field that interacts with background plasma governed by a set of reduced MHD equations. Only the fraction of current carried by the bulk plasma is affected by resistivity. The linear and nonlinear properties of resistive hose mode are systematically investigated under different conditions. It is found that the resistive hose mode can saturate in a turbulent state. The nonlinear dynamics have all been discussed in detail. The nonlinear coupling between the resistive hose mode and TM is also discussed.