Analytical model of plasma response to external magnetic perturbation in absence of no-slip condition

TL;DR

This paper develops a new nonlinear model for plasma response to external magnetic perturbations without assuming the no-slip condition, integrating island evolution and plasma flow dynamics across different regimes.

Contribution

It introduces a comprehensive theoretical framework that accounts for the absence of no-slip condition, combining island evolution, plasma flow, and electromagnetic forces in plasma response modeling.

Findings

Island growth governed by linear or Rutherford theory depending on size

Island oscillation frequency can differ from plasma flow frequency

Model captures nonlinear plasma response without no-slip assumption

Abstract

Recent simulation and experimental results suggest that the magnetic island and flow on resonant surface often do not satisfy the "no-slip" condition in the steady state. A new theory model on nonlinear plasma response to external magnetic perturbation in absence of no-slip condition is proposed. The model is composed of the equations for the evolution of both width and phase of magnetic island due to forced reconnection driven by the external magnetic perturbation, and the force-balance equation for the plasma flow. When the island width is much less than the resistive layer width, the island growth is governed by the linear Hahm-Kulsrud-Taylor solution in presence of time-dependent plasma flow. In the other regime when the island width is much larger than the resistive layer width, the evolution of both island width and phase can be described using the Rutherford theory. The island solution is used to construct the quasi-linear electromagnetic force, which together with viscous one, contributes to the nonlinear variation in plasma flow. The no-slip condition assumed in the conventional error field theory is not imposed here, where the island oscillation frequency depends on but does not necessarily equal to the plasma flow frequency at the rational surface.