Dynamics of magnetic relaxation in a high-temperature, current-carrying plasma

Abstract

The results of a study of the role of multiple-helicity nonlinear interaction of tearing modes and the dynamics of magnetic relaxation and dynamo activity in a high-temperature, current-carrying plasma are described. A set of fluid equations for tearing modes in the semicollisional regime is derived, and a previous resistive magnetohydrodynamic study of tearing mode turbulence is thus extended to high-temperature regimes. Because of the direct connection between fluctuation evolution and configuration evolution, a generalized nonlinear theory of the turbulent dynamo and magnetic relaxation is proposed, and a two-point 〈(∇⊥p̃)ψ̃〉-correlation evolution is determined by calculating the relaxation time τcl. This calculated relaxation time is shown to serve as the phase shift between ṽr and ψ̃ and hence to control magnetic energy relaxation and dynamo processes. Careful study of the two separated regions of kink-tearing modes (i.e., the resonant region and the exterior region) reveals the direct relationship between the equilibrium magnetic energy relaxation and average magnetic flux evolution. Thus a theoretical interpretation of the observed correlation between magnetic fluctuations and maintenance of field reversal is provided. Finally, the correlation lifetime of the flux transport term is evaluated from the renormalized two-point theory, and the saturated magnetic fluctuation level is estimated. The result shows that the saturation level is independent of or very weakly dependent on the Lundquist number S. The implications of this result for anomalous thermal transport and dynamo activity in high-temperature reversed field pinch experiments are discussed.