Force scaling for n = 0 RWMs

Abstract

For a given sequence of vertically unstable plasma equilibria with increasing plasma elongation (κ) and a fixed plasma boundary-wall gap (Δ), the net vertical force per unit plasma displacement acting on the resistive wall is non-monotonic with κ. In particular, exhibits a maximum near of γτw ≈ 1/ms ≈ 1, where γ is the plasma vertical instability growth rate, τw is the magnetic field diffusion time constant through the resistive shell and ms is the plasma stability margin (Portone A. 2005 Nucl. Fusion 45 926–32). This (not intuitive) result confirms previous theoretical (Mironov D V and Pustovitov V D 2017 Phys. Plasmas 24 092508) and numerical findings (Strauss H R et al 2010 Phys. Plasmas 17 082505) obtained for general n = 1 kink modes and it provides an upper bound on the electro-magnetic loads induced on the stabilizing structures by vertical displacements (without halo currents) for a given plasma current.