OBSERVATION OF AN UNSTABLE L = 1 DIOCOTRON MODE ON A HOLLOW ELECTRON COLUMN

Stable and unstable diocotron modes varying as eil, with l=1, are measured on a magnetized, partially hollow electron column. The unstable mode is observed to grow exponentially over several decades, in contradiction to present 2 D fluid theory. This l=1 instability can dominate the evolution well into the nonlinear regime, resulting in cross-field transport to a stable, monotonically decreasing density profile. To the extent this process is described by 2D E×B drifts, it is isomorphic to the Kelvin-Helmholtz shear-flow instability of inviscid fluids. © 1990 The American Physical Society.