Topological Arrest of Ballooning Modes in Non-Axisymmetric Plasmas

TL;DR

The paper explains how 3D geometry in stellarators localizes ballooning modes, transforming global instabilities into isolated packets, and introduces a percolation-based stability threshold relevant for reactor design.

Contribution

It reveals the role of Anderson localization in stabilizing non-axisymmetric plasmas and proposes a new nonlinear stability metric based on percolation theory.

Findings

Localization of ballooning modes reduces global instability.

A critical threshold determines stability or crash in stellarators.

The approach predicts stability vulnerabilities in certain designs.

Abstract

Why do non-axisymmetric stellarators avoid ballooning crashes that afflict tokamaks? Three-dimensional geometry induces Anderson localization of ballooning modes, converting a global instability into a Ginzburg--Landau network of isolated wave packets. Global stability reduces to a percolation problem: below a critical threshold, instability is arrested; above it, a crash occurs. This explains benign stellarator saturation, predicts vulnerability in quasisymmetric designs, and introduces the critical threshold as a nonlinear stability metric for reactor optimization, pending experimental validation.