Helical temperature perturbations associated with tearing modes in tokamak plasmas

TLDR

The study investigates electron temperature perturbations linked to tearing modes in tokamak plasmas. The perturbations arise from magnetic field line stagnation near the rational surface combined with finite parallel thermal conductivity. A critical island width exists below which temperature flattening fails, such islands are not destabilized by perturbed bootstrap current, and this explains certain error‑field reconnection observations; the width is substantial when accounting for long mean‑free‑path parallel heat transport and anomalous perpendicular transport.

Abstract

An investigation is made into the electron temperature perturbations associated with tearing modes in tokamak plasmas. It is found that there is a critical magnetic island width below which the conventional picture where the temperature is flattened inside the separatrix is invalid. This effect comes about because of the stagnation of magnetic field lines in the vicinity of the rational surface and the finite parallel thermal conductivity of the plasma. Islands whose widths lie below the critical value are not destabilized by the perturbed bootstrap current, unlike conventional magnetic islands. This effect may provide an explanation for some puzzling experimental results regarding error field-induced magnetic reconnection. The critical island width is found to be fairly substantial in conventional tokamak plasmas, provided that the long mean-free path nature of parallel heat transport and the anomalous nature of perpendicular heat transport are taken into account in the calculation.