Explosive Ballooning Flux Tubes in Tokamaks

TL;DR

This paper investigates the stability of magnetic flux tubes in tokamaks, revealing conditions under which they become metastable or unstable, potentially leading to rapid plasma confinement loss.

Contribution

It introduces a detailed analysis of ballooning flux tube stability in tokamaks, identifying critical pressure gradients for metastability and instability.

Findings

Metastability occurs above a certain pressure gradient due to finite displacements.

Linear and nonlinear instability arise at higher pressure gradients.

Displacements can be comparable to the pressure gradient scale length.

Abstract

Tokamak stability to, potentially explosive, `ballooning' displacements of elliptical magnetic flux tubes is examined in large aspect ratio equilibrium. Above a critical pressure gradient the energy stored in the plasma may be lowered by finite (but not infinitesimal) displacements of such tubes (metastability). Above a higher pressure gradient, the linear stability boundary, such tubes are linearly and nonlinearly unstable. The flux tube displacement can be of the order of the pressure gradient scale length. Plasma transport from displaced flux tubes may result in rapid loss of confinement.