The compressible evolution of the super-Alfvenic magnetized wake

R.B. Dahlburg, R. Keppens, G. Einaudi

submitted to Physics of Plasmas, 2000

The effects of compressibility on the linear and nonlinear properties of the magnetized wake are examined, with an emphasis on the high speed flow situation. It is found that compressibility can modify properties of this system previously identified for the incompressible case. Of particular interest is an investigation of how the properties of the magnetized wake vary with the sonic Mach number. It is found that, in general, the growth rates of the unstable sinuous and varicose modes decrease with increasing Mach number and with increasing Alfven number. However, at high sonic Mach numbers the varicose modes can have a growth rate which increases as the spanwise wavenumber increases, a significant difference from the incompressible case.

The linear compressible equations are solved by a modified version of the SPEctral Compressible Linear Stability (SPECLS) algorithm, a Chebyshev collocation code. Nonlinear computations based on the Versatile Advection Code (VAC) are also presented. Growth rates computed by both codes in the linear regime are in excellent agreement. At long times the system relaminarizes to an overall accelerated and broadened wake channel. It is found that variations in the Mach and Alfven numbers have a strong affect on the evolution of the magnetized wake, e.g., for high M fast magnetosonic shocks are observed to develop.