Linear NIMROD simulations of n = 0 modes for straight tokamak configuration and comparison with analytic results

Comparison between the analytic theory of n = 0 vertical displacement modes in magnetically confined plasmas of fusion interest and numerical simulations using the extended-MHD code NIMROD is presented. Agreement between analytic and numerical results is highly satisfactory. Differences are interpreted to be caused mostly by the different wall shape and by the presence of a halo plasma surrounding the hot plasma adopted in NIMROD. A numerical study of vertical displacement oscillatory modes [Barberis et al., J. Plasma Phys. 88, 905880511 (2022)] is presented. Axisymmetric X-point currents supported by the halo plasma are discussed. The article provides a successful benchmark and a useful starting point for future numerical investigations of n = 0 modes using more realistic tokamak geometry and plasma equilibria.