An efficient MHD equilibrium solver for control oriented transport models

Abstract

In tokamak plasmas, the current density profile is a strong determiner of both MHD stability and confinement. The design of active control techniques for this profile relies on control oriented transport models that capture the essential dynamics of its evolution. The physics of transport is coupled to the MHD equilibrium that determines the spatial structure of the magnetic configuration. However, since this coupling is difficult to solve, the common practice is not to update the equilibrium condition during profile control design or current profile tracking. In this work, a simplified coupling scheme for transport and equilibrium suitable for internal profile control design is proposed. The scheme relies on a new MHD equilibrium solver that efficiently updates the magnetic configuration using the safety factor and pressure profiles computed by the control oriented transport code. The new solver is described in detail and validated in advanced tokamak conditions including challenging features like reversed magnetic shear in the plasma core, edge transport barrier and high plasma beta.