Adelle Wright, Princeton Plasma Physics Laboratory.

"Nonlinear MHD theory and modeling in the presence of 3D magnetic fields"

Abstract: Plasma confinement properties in tokamaks and stellarators can be profoundly impacted by symmetry-breaking magnetic field perturbations that are generated both externally, e.g., by resonant magnetic perturbations (RMPs) or error fields, and by magnetohydrodynamic (MHD) instabilities. While this makes understanding MHD dynamics and nonlinear stability in the presence of 3D magnetic fields (which may contain a mixture of magnetic surfaces, islands and chaos) essential for fusion, it remains a frontier challenge both theoretically and numerically.

Modeling 3D fields using equilibrium principles provides speed and computational efficiency – characteristics which are essential for optimization and some reconstruction applications – at the expense of guaranteeing dynamical accessibility and may predict plasma states that cannot be accessed in experiment.

On the other hand, initial-value methods which solve high fidelity macroscopic models (e.g., extended-MHD) capture the self-consistent evolution of plasma profiles and thus guarantee dynamically accessible states, however, are highly resource intensive.
In this talk, we present recent developments in nonlinear MHD theory and modeling in the presence of 3D magnetic fields which overcome these challenges.

We consider the prospects for efficient calculation of the 3D plasma response to RMPs using equilibrium principles based on energy minimization, by comparing the Stepped Pressure Equilibrium Code with the extended-MHD code, M3D-C1.

We introduce the M3D-C1 code’s new capability to perform extended-MHD simulations in stellarator geometry, presenting the first results from a parametric exploration of β-limits in a 10-field period heliotron. Motivated by results from these simulations, we examine the formation of chaotic magnetic fields using a new method for predicting unstable pressure-driven MHD modes in low shear equilibria.