Large-scale fixed point of forced plasmas

Abstract

The stable infrared state of a forced magnetohydrodynamic (MHD) plasma is explored in the long-time and large-scale limit. Large-scale fluctuations are important as they may regulate or deteriorate the turbulent plasma states. This work is motivated by recent studies on drift-Alfven modes and drift-tearing modes in the context of the generation of large-scale fluctuations, like zonal flows. The Gaussian random noise of the power-law spectrum is supplied, and the viscosity, the resistivity, the fields, and the noise are renormalized by regularizng the divergent Green's functions and the couplings. A stable fixed point is found, and the ratio of the resistivity to the viscosity and the strength of the noise are obtained. As a result, the magnetic energy spectrum is shown to be steeper than the kinetic energy due to the renormalization of the Lorentz force. We argue that the hump in the total energy spectrum may be partially explained by the difference in the two energy scalings.