Drift wave vortices in nonuniform plasmas with sheared magnetic fields

Abstract

Nonlinear coherent structures governed by the coupled drift wave–ion-acoustic mode equations in nonuniform plasmas with sheared magnetic fields are studied analytically and numerically. A solitary vortex equation that includes the effects of density and temperature gradients and magnetic shear is derived and analyzed. The analytic and numerical studies show that for a plasma in a sheared magnetic field, even without the temperature and drift velocity gradients, solitary vortex solutions are possible; however, these solutions are not exponentially localized due to the presence of a nonstructurally stable perturbative tail that connects to the core of the vortex. The new coherent vortex structures are dipolelike in their symmetry, but are not the modons of Larichev and Reznik. In the presence of a small temperature or drift velocity gradient, the new shear-induced dipole cannot survive and will separate into monopoles, like the case of the modon in a sheared drift velocity as studied in Su et al. [Phys. Fluids B 3, 921 (1991)]. The solitary solutions are found from the nonlinear eigenvalue problem for the effective potential in a quasi-one-dimensional approximation. The numerical simulations are performed in two dimensions with the coupled vorticity and parallel mass flow equations.