Strong "Quantum" Chaos in the Global Ballooning Mode Spectrum of Three-dimensional Plasmas
Authors: R.L. Dewar, P. Cuthbert, and R. Ball
Date of PPPL Report: November 2000
Published in: Phys. Rev. Lett. 86 (12 March 2001) 2321-2324.
The spectrum of ideal magnetohydrodynamic (MHD) pressure-driven (ballooning) modes in strongly nonaxisymmetric toroidal systems is difficult to analyze numerically owing to the singular nature of ideal MHD caused by lack of an inherent scale length. In this paper, ideal MHD is regularized by using a k-space cutoff, making the ray tracing for the WKB ballooning formalism a chaotic Hamiltonian billiard problem. The minimum width of the toroidal Fourier spectrum needed for resolving toroidally localized ballooning modes with a global eigenvalue code is estimated from the Weyl formula. This phase-space-volume estimation method is applied to ballooning-unstable plasma equilibria in the H-1NF helical axis stellarator and the Large Helical Device (LHD).