April 29, 2:00pm - 3:00 pm, Room 242

April 29, 2:00pm - 3:00 pm, Room 242

Effects of Weak Collisions on Nonlinear Kinetic Plasma Dynamics

Carrie Black (University of New Hampshire, Space Science Center)

Kinetic plasma behaviors have long been of interest to those studying space and laboratory plasmas. For instance, kinetic plasma instabilities are widely believed to be responsible for the generation of anomalous resistivity in reconnection layers, providing a possible mechanism for fast reconnection. The concept of Landau damping is fundamental to such wave kinetic instabilities in space, and is treated typically within the framework of the collisionless Vlasov equation. It has become clear in recent theoretical and experimental work that weak collisions are a singular perturbation on the collisionless theory, and qualitatively alter the results of the collisionless theory. In particular, it has been demonstrated by C. S. Ng, A. Bhattacharjee, and F. Skiff that the Case-Van Kampen continuous spectrum, which are the underlying eignemodes of the collisionless system, are completely eliminated and replaced by a discrete spectrum (hereafter referred to as the NBS spectrum). The NBS spectrum includes Landau-damped roots as exact eigenmodes, but is significantly broader, including a larger spectrum of discrete roots. We discuss the implications of these results for two nonlinear applications, the plasma wave echo and the ion acoustic instability, by means of a new Vlasov code that has been modified to include the Lenard-Bernstein collision operator. We show that the existing collisional theories for the echo, which fail to account for the discrete collisional spectrum, do not yield the appropriate collisional damping rates. Of greater practical importance to problems involving reconnection in space plasmas is the ion acoustic wave and its associated anomalous resistivity. We compare our numerical findings with the analytical and numerical work on the subject, quantifying the effect of weak collisions.