Passive mitigation of VDE current quench forces in vacuum vessels with helical insulating bands

Disruptions remain a significant threat to the viability of economic fusion energy, due to the potential for damage to reactor structure and components. While the majority of disruption mitigation studies focus on active systems, passive conducting structures for the mitigation of runaway electrons are planned on multiple new/existing devices [1]. In this work, we explore a philosophically similar approach to the mitigation of current quench eddy forces. By engineering helical electrically insulating bands into the vacuum vessel, coupling between the plasma and vacuum vessel during disruption can be limited purely to the fundamental zeroth eigenmode of the current quench, bypassing any coupling to vertical motion. To validate this, time-dependent Grad-Shafranov simulations of vertical displacement events (VDEs) were carried out in TokaMaker [2]. We demonstrate a passive reduction in disruption forces as compared to an identical uniformly conductive vacuum vessel. When passive stabilizing structures are included outside the vacuum vessel, this reduction in forces on the vessel comes at no cost to overall plasma vertical stability as well. This reduction in mechanical demand potentially expands the space of viable designs for vacuum vessels, allowing for more focus on thermodynamic and economic efficiency.

[1] V. A. Izzo et al. 2024 Nucl. Fusion 64 066003

[2] C. J. Hansen et al. Comput. Phys. Commun. 298 (2024) 109111