External charge perturbation in a flowing plasma and electrostatic turbulence

In this work, a 1D electrostatic hybrid-particle-in-cell-Monte Carlo collision code is used to study the response of a plasma to a moving, external, charged perturbation (debris). We show that the so-called pinned solitons can form only under certain specific conditions through a turbulent regime of the ion–ion counterstreaming electrostatic instability. In fact, the pinned solitons are manifestations of the ion phase-space vortices formed around the debris. The simulation shows that the pinned solitons can form only when the debris charge density exceeds a certain value causing the counterstreaming ion velocity to exceed a critical velocity, pushing the instability to a turbulent regime. The effect of debris velocity is also essential for the appearance of pinned soliton as when the debris velocity increases, it causes the widening of the phase space vortices causing well-separated pinned solitons, which merge to form one single soliton when debris velocity reduces to zero. In the opposite extreme, when debris velocity becomes highly supersonic, the vortices are widened up to a limit causing the pinned solitons to disappear altogether. We further show the existence of a Kolmogorov-type energy cascade scaling for this electrostatic turbulence.