Cascading of Fast‐Mode Balanced and Imbalanced Turbulence

We study the cascading of fast MHD modes in magnetically dominated plasma byperforming one-dimensional (1D) dynamical simulations. We find that thecascading becomes more efficient as an angle between wave vector and underlyingmagnetic field increases and fast mode becomes more compressive. We also studyimbalanced turbulence, in which wave packets propagating in one-direction havemore power than those in the opposite direction. Unlike imbalanced \Alfvenicturbulence, the imbalanced fast mode turbulence shows faster cascading as thedegree of imbalance increases. We find that the spectral index of the velocityand magnetic field, which are carried by the fast-mode turbulence, quicklyreaches stationary value of -2. Thus we conclude that the dissipation of fastmode, at least in 1D case, happens not due to weak or strong turbulentcascading, but mostly due to nonlinear steepening. The density fluctuations,which are carried by slow-mode perturbation in the larger scale andentropy-mode perturbation in the smaller scale, depend on initial drivingspectrum and a ratio of specific heat.Comment: 8 pages, 10 figures embedded (emulateapj style), submitted to Ap