Magnetic compressibility and ion-temperature-gradient-driven microinstabilities in magnetically confined plasmas

TL;DR

This paper develops an electromagnetic theory for ion-temperature-gradient-driven microinstabilities in magnetically confined plasmas, identifying stabilization effects related to plasma beta and magnetic shear, with implications for plasma confinement stability.

Contribution

It introduces a comprehensive electromagnetic framework for ITG instabilities, including a critical beta threshold for stabilization and effects of magnetic shear on stability boundaries.

Findings

Critical beta for mode stabilization scales with electron temperature gradient length and major radius.

Fast particle populations may also stabilize modes through pressure gradient effects.

Stability boundaries depend on magnetic shear and curvature along magnetic field lines.

Abstract

The electromagnetic theory of the strongly driven ion-temperature-gradient (ITG) instability in magnetically confined toroidal plasmas is developed. Stabilizing and destabilizing effects are identified, and a critical $\beta_{e}$ (the ratio of the electron to magnetic pressure) for stabilization of the toroidal branch of the mode is calculated for magnetic equilibria independent of the coordinate along the magnetic field. Its scaling is $\beta_{e}\sim L_{Te}/R,$ where $L_{Te}$ is the characteristic electron temperature gradient length, and $R$ the major radius of the torus. We conjecture that a fast particle population can cause a similar stabilization due to its contribution to the equilibrium pressure gradient. For sheared equilibria, the boundary of marginal stability of the electromagnetic correction to the electrostatic mode is also given. For a general magnetic equilibrium, we find a critical length (for electromagnetic stabilization) of the extent of the unfavourable curvature along the magnetic field. This is a decreasing function of the local magnetic shear.