Formation of a broad plasma turbulent layer by forward and inverse energy cascades of the Kelvin–Helmholtz instability

Abstract

The 2‐D MHD simulations of the Kelvin–Helmholtz instability (KHI) with transverse magnetic field and highly asymmetric density configurations in a large simulation domain show that rapid formation of a broad plasma turbulent layer can be achieved by forward and inverse energy cascades of the KHI. The forward cascade is triggered by growth of the secondary Rayleigh‐Taylor instability excited during the nonlinear evolution of the KHI. The inverse cascade is accomplished by nonlinear mode couplings between the fastest growing mode of the KHI and other KH unstable modes. As a result of the energy transport by the inverse cascade, the growth rate of the largest vortex allowed in the system reaches 3.7 times as large as the linear growth rate. A PIC simulation under the similar initial configuration is also conducted and shows the quick growth of the largest vortex and the resultant spread of the turbulent layer in which plasmas are effectively mixed. The proposed mechanism enables rapid formation of a large scale mixing layer which resembles observational characteristics of the low‐latitude boundary layer of the magnetosphere.