Nonlinear wake potential in a dusty plasma

The linear response of a dust grain to a flowing plasma has been well studied, both through analytic theory as well as by plasma simulation. The principal feature of the plasma response is a quasi-periodic wavetrain downstream of the grain, whose characteristics have been investigated as a function of the plasma conditions and grain properties. In linear theory, the magnitude of the wake potential scales as the grain charge Q. For large enough charge, one expects that nonlinear behavior will occur. Using one- and two-dimensional simulations with particle ions flowing past a fixed charged grain, we show that for sufficiently large Q, the wake potential becomes essentially independent of the grain charge. The potential is large enough to reflect some of the incident ions, which become trapped in the vicinity of the grain. Compared to our previous calculations, we also assume a larger value for the ion-neutral collision frequency, and show that the resulting wake is significantly shorter in length and steadier in time