Formulation and numerical benchmark of improved magneto-fluid boundary conditions for 3D nonlinear MHD code SPECYL

3D nonlinear MHD code SPECYL boundary conditions BCs have been increasingly made more realistic, from traditional SpeCyl.1 (ideal conductor facing plasma) to modelling plasma vacuum interface as a resistive thin shell. Linear benchmark against ideal MHD ( 𝜂_𝑝𝑙asma , 𝜈_𝑝𝑙asma→0) suggested the need for finite plasma edge 𝑉𝑟. We present the resulting BCs, here dubbed SpeCyl.2. Verification of SpeCyl.2 against another code (Pixie3D), enforcing analogous physical assumptions in BCs, is also shown. This amends some unphysical idealities of SpeCyl.1 and completes what already done in 2010, in a formerly published mutual benchmark of the two codes. Linear benchmark against the theory of ideal MHD instabilities is presented, featuring a pseudo-vacuum low-density layer at plasma edge, in analogy to what is done in other codes.