Topological Arrest of Ballooning Modes in Non-Axisymmetric Plasmas

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.