Magnetic field line chaos and fusion power

Fusion power may be generated in steady-state by confining hot plasmas using only external magnetic fields. These can be tailored in such a way that magnetic field lines foliate toroidally nested surfaces that act as energy barriers for the plasma. This is the idea behind the stellarator concept, which has experienced a renaissance in recent years, and has brought up new mathematical and physical questions. Of particular importance is the calculation of equilibrium pressure limits. Indeed, at sufficiently high pressure a plasma generates currents that promote the destruction of magnetic surfaces and the emergence magnetic chaos, thereby degrading plasma confinement. These phenomena can be modeled with three-dimensional magneto-hydrodynamics, which is a fantastic numerical challenge. In this talk I will illustrate how we can predict and characterize the emergence of magnetic chaos at high plasma pressures in toroidally confined plasmas, and how we can attempt at optimizing the external magnetic field to increase the pressure limit.