IFS Seminar

Abstract:
In analyzing stellarator configurations, it is common to perform an asymptotic expansion about the magnetic axis. This so-called near-axis expansion is convenient for the same reason asymptotic expansions often are: it reduces the dimension of the problem. Analytically, this means that physical quantities such as particle confinement (quasisymmetry) and stability criteria are easily expressed. Computationally, the near-axis expansion allows for an approximate stellarator configuration at a speed unmatched by the standard 3D equilibrium solvers.

Unfortunately, it has been repeatedly found that the expansion diverges at high orders, limiting the physics the expansion can describe. In this talk, I will show how the near-axis expansion diverges in vacuum due to ill-posedness, and that can be regularized to improve its convergence. Then, using stellarator coil sets, I will show that the near-axis expansion can converge to ninth order in the magnetic field, giving accurate high-order corrections to the computation of flux surfaces.