Magnetohydrodynamic Stability of Free-Boundary Quasi-Axisymmetric Stellarator Equilibria with Finite Bootstrap Current

The impact of the bootstrap current is investigated on the equilibrium properties of a two-period quasi-axisymmetric stellarator reactor with free boundary and on the corresponding ideal magnetohydrodynamic stability properties. Although the magnetic field strength B spectrum is dominated by a m/n = 1/0 component, the discrete filamentary coils trigger some smallamplitude symmetry-breaking components that can disturb the quasi-symmetry of B. Finite (beta) causes the plasma column to shift outward in the absence of bootstrap current. With a self-consistent bootstrap current in the 1/v regime, the plasma becomes more elongated and more distorted in the horizontally elongated up-down symmetric cross section. At (beta) [approximately equal to] 3.25%, the plasma can be restored to its near-vacuum shape with the application of a vertical field with coil currents 20% of those of the modular coils, but at the expense of a significant mirror component in the B-field spectrum.