J. Virtamo

Bio: J. Virtamo is an academic researcher from Max Planck Society. The author has contributed to research in topics: Free energy principle & Euler equations. The author has an hindex of 1, co-authored 1 publications receiving 15 citations.

Energy Principle for 3-d Resistive Instabilities in Shaped-cross-section Tokamaks

Abstract: An energy principle for 'helical' incompressible perturbations in shaped cross-section plasmas is derived in the Tokamak scaling ( epsilon identical to ka approximately=Bperpendicular to /Bz<<1). Two models for the resistivity are used. The resistivity is assumed to be transported either by the fluid or by the magnetic surfaces. In the first case generalized rippling and tearing modes are discovered, while in the latter case the rippling is cancelled in a self-consistent way. The Euler equation for the tearing modes generalizes the previously derived equation for two-dimensional perturbations. It is pointed out that the energy principle cannot be extended to higher orders in epsilon .

The resistive tearing instability for generalized resistivity models: Theory

Abstract: In collision‐dominated plasmas, as well as in plasma systems with anomalous dissipation, the resistivity, in general, depends on the local plasma parameters. Except for some special applications, this dependence is usually not taken into account for the resistive tearing mode. In this paper, a dispersion relation for the resistive tearing mode is derived in a closed analytical form, where generalized models for the resistivity are considered. Because of the dependence on electron temperature, e.g., for the Spitzer resistivity, a further transport equation for the electron temperature is assumed in the presented theory. For applications to more realistic systems, the equilibrium configuration is assumed to be weakly two dimensional. Thus the obtained dispersion relation represents a generalization, which includes a number of results of previous authors. In order to determine this dispersion relation, a constant Ψ approximation is not applied such that the parameter regime of maximum growth rate is covered by the presented theory.

Tearing Mode Stability for Arbitrary Current Distribution

Abstract: The linear tearing mode stability is evaluated for 1D equilibria in cylindrical geometry with arbitrary current profiles. This treatment combines the energy method and the Ritz-Galerkin procedure using finite elements. Particularly for hollow currents with two singular q surfaces extremely accurate results showing the coupling influence of both singularities are obtained.