On the drift-sausage mode in one-dimensional current sheet

This article presents a two-fluid stability analysis of Harris current shee t equilibrium under the assumption of charge quasi-neutrality, It is found that the charge neutrality condition leads to sausage-type fluctuations, wh ich propagate along the direction of the cross-field current flow, hence th e drift-sausage mode. It is also shown that solutions which correspond to k ink-type perturbations do not exist under the present assumption of charge neutrality. In view of the fact that a substantial body of simulation works exist which report predominantly kink-like perturbations, and that analyti cal theories which do not assume charge quasi-neutrality predict that the k ink-type mode is a dominant unstable mode, it is concluded that the assumpt ion of quasi-neutrality may be a poor choice in describing the stability of Harris current sheet equilibrium.