Axisymmetric Plasma Equilibria with Toroidal and Poloidal Velocity Fields: Tokamak Relevant Configurations

TL;DR

This paper investigates axisymmetric plasma equilibria with combined toroidal and poloidal velocities, revealing a new confinement regime near X-points that could enhance tokamak performance.

Contribution

It introduces a modified Grad-Shafranov equation for plasma with velocity fields aligned with magnetic lines, applied to tokamak-like profiles, highlighting a novel equilibrium regime.

Findings

Emergence of a null pressure surface with X-points in double-null configurations

Potential for improved plasma confinement near X-points

Reduced power transfer to the divertor in the new regime

Abstract

We analyze an axisymmetric equilibrium of a plasma endowed with toroidal and poloidal velocity fields, with the aim to characterize the influence of the global motion on the morphology of the magnetic confinement. We construct our configuration assuming that the poloidal velocity field is aligned with the poloidal magnetic field lines and, furthermore, we require that the plasma mass density depend on the magnetic flux function (or equivalently, that the plasma fluid be incompressible). We then derive a sort of Grad-Shafranov equation for such an equilibrium and implement it to tokamak relevant situations, with particular reference to TCV-like profiles. The main result of the present study concerns the emergence, in configurations associated to a double-null profile, of a closed surface of null pressure encorporating the two X-points of the magnetic configuration. This scenario suggests the possible existence of a new regime of the plasma equilibrium, corresponding to an improved plasma confinement near the X-points and a consequent reduced power transfer to the tokamak divertor.