The DCON3D code for the ideal MHD stability of stellarator equilibria with nested flux surfaces

This publication describes the DCON3D code for determination of the ideal MHD stability of stellarators with nested flux surfaces. The direct criterion of Newcomb was originally presented for one-dimensional cylindrical screw-pinch equilibria depending only on cylindrical radius r. It was extended with the DCON code to two-dimensional axisymmetric tokamak equilibria depending on toroidal flux coordinates (ψ,θ). This work further extends the approach to nonaxisymmetric stellarator equilibria with nested flux surfaces, depending on toroidal flux coordinates (ρ,θ,ζ). It provides a very fast and accurate method to determine the existence of instabilities without the need to compute eigenvalues and eigenfunctions.