The Hodge decomposition of shell current on the Keda Torus eXperiment device

Abstract

The Hodge decomposition is a valuable tool for uniquely decomposing total currents on the composite shell into three types: inductive current, halo current, and harmonic current, each with its specific physical meaning. During plasma disruptions, halo currents appear, essential for studying the wall’s thermal load and electromagnetic force. Furthermore, understanding halo currents is crucial for improving the existing methodologies by removing their effects on equilibrium reconstructions and instability analyses based on boundary magnetic probe data. On the Keda Torus eXperiment (KTX) device, radial and tangent halo currents can be simultaneously provided to locate the contact region during a minor disruption experimentally. Additionally, experimental results demonstrate that, in addition to the occurrence of halo current during minor disruption events, halo current is already present simultaneously with the generation of inductive current when a resistive wall mode exists. For devices that lack the capability to measure the two-dimensional shell current distribution on the entire shell, we propose a method to estimate inductive and halo currents only using a set of shell currents along the toroidal direction. This technique is demonstrated on the KTX device and provides an overall good approximation of the inductive and halo current distribution.