Finite beta MHD equilibrium and stability analyses of optimized stellarator plasmas

Accurate predictions of the neoclassical bootstrap current and ambipolar radial electric field are essential for modeling the steady-state equilibrium and stability of finite-beta stellarator plasmas. The bootstrap current arises from momentum transfer between bouncing (trapped) and passing particles on a flux surface. In 3-D configurations such as quasi-omnigenous and quasi-symmetric stellarators, the ambipolar radial electric field has multiple stable solutions which influence the predicted species-dependent and net parallel flows and current. High-fidelity transport modeling informs the plasma profiles which are key to identifying the self-consistent bootstrap current and its anticipated effects on the rotational transform, core equilibrium and transport properties, and modifications to the edge geometry. Beyond basic equilibrium considerations, the Mercier criterion, ballooning stability and global MHD modes can all play roles in setting limits on the expected operational space of specific configurations.