Role of Cross Helicity in Cascade Processes of MHD turbulence

TL;DR

This paper explores how cross helicity influences energy transfer in isotropic MHD turbulence, revealing that it blocks spectral energy transfer, causes energy accumulation, and alters the turbulence spectrum slope.

Contribution

It introduces a formula to estimate turbulence energy based on the ratio of injected helicity to energy and analyzes how cross helicity affects spectral properties.

Findings

Cross helicity blocks spectral energy transfer in MHD turbulence.

Energy accumulates until vortex intensification balances nonlinear interactions.

Spectrum slope increases from 5/3 to 2 with higher cross helicity levels.

Abstract

The purpose of this work is to investigate the spectral properties of the developed isotropic (non-Alfven) MHD turbulence stationary excited by an external force, which injects the cross helicity into the flow simultaneously with the energy. It is shown that the cross helicity blocks the spectral energy transfer in MHD turbulence and results in energy accumulation in the system. This accumulation proceeds until the vortex intensification compensates the decreasing efficiency of nonlinear interactions. The formula for estimating the average turbulence energy is obtained for the set ratio between the injected helicity and energy. It is remarkable that the turbulence accumulates the injected cross helicity at its low rate injection -- the integral correlation coefficient significantly exceeds the ratio between the injected helicity and the energy. It is shown that the spectrum slope gradually increases from "5/3" to "2" with the cross helicity level.