Numerical equilibria with pressure anisotropy and incompressible plasma rotation parallel to the magnetic field

TL;DR

This paper develops a numerical method to analyze plasma equilibria in tokamaks considering pressure anisotropy and parallel rotation, revealing how these factors influence confinement and stability.

Contribution

It extends the HELENA equilibrium solver to incorporate pressure anisotropy and parallel rotation, providing new insights into their effects on plasma equilibrium profiles.

Findings

Pressure anisotropy enhances profile shaping and confinement.

Anisotropy has a stronger impact on equilibrium quantities than rotation.

Parallel heating influences current density and stability.

Abstract

It is believed that plasma rotation can affect the transitions to the advanced confinement regimes in tokamaks. In addition, in order to achieve fusion temperatures modern tokamaks rely on auxiliary heating methods. These methods generate pressure anisotropy in the plasma. For incompressible rotation with pressure anisotropy the equilibrium is governed by a Generalized Grad-Shafranov (GGS) equation and a decoupled Bernoulli-type equation for the effective pressure, $\bar{p}=(p_\parallel+p_\perp)/2$, where $p_\parallel$ ($p_\perp$) is the pressure tensor element parallel (perpendicular) to the magnetic field. In the case of plasma rotation parallel to the magnetic field the GGS equation can be transformed to one equation identical in form with the GS equation. In this study by making use of the aforementioned property of the GGS equation for parallel plasma rotation we have constructed ITER-like numerical equilibria by extending HELENA, an equilibrium fixed-boundary solver and examined the impact of rotation and anisotropy on certain equilibrium quantities. The main conclusions are that the addition of pressure anisotropy to rotation allows the profile shaping of the equilibrium quantities in much more extent thus favouring the confinement and allows extension of the parametric space of the Mach number corresponding to higher values. Furthermore, the impact of pressure anisotropy in the equilibrium quantities is stronger than that of the rotation, for most of the quantities examined. For the pressure components the impact of the pressure anisotropy is the same regardless of whether the power is deposited parallel or perpendicular to the magnetic surfaces, thus implying that there is no preferable heating direction, while for the current density, the heating parallel to the magnetic surfaces seems to be beneficial for the current-gradient driven instabilities.