National Institutes of Natural Science, National Institute for Fusion Science
Department of Helical Plasma Research, Fundamental Physics Simulation Research Division

Extended MHD modeling

Effects of Finite Larmor Radius on Equilibria with Flow in Reduced Two-Fluid Models

For steep plasma profiles in improved confinement modes of magnetically confined plasmas, small-scale effects not included in the ideal magnetohydrodynamic (MHD) model could be significant. Our goal is to model actual equilibria in more detail by extending the MHD model to include the small-scale effects relevant to fusion plasmas.
Figures (a) ? (c) show the numerical solutions of the equations for flowing equilibria with effects of two-fluid and ion finite radius: (a) magnetic flux surfaces, (b) pressure isosurfaces and (c) isosurfaces of the ion stream function at a poloidal cross-section of the torus. Flows in plasmas may play important roles for sustaining steep profiles. The results show the flow causes the departure of pressure isosurfaces from the magnetic flux surfaces and the isosurfaces of the ion stream funcion do not coincide with the magnetic flux surfaces due to the small scale effects. These complex equilibrium structures different from the standard MHD static equilibria have been given by the derivation of the equilibrium equations by asymptotic expansions and the numerical analysis with a finite element method.

A. Ito and N. Nakajima, AIP Conference Proceedings Vol. 1069, pp.121 (2008).

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