Formation of Rotating Plasma in Crossed Field

Abstract

The present paper describes the formation process of a rotating plasma in a homopolar-like short coaxial-electrode system carried out in a H₂, N₂ or A discharge. A Kerr cell shutter with a 50 ns exposure time was used for optical records. It is found that the process is divided into two stages: first a negative streamer appears and develops to a spoke, and later the spoke spreads to a disk. The streamer process is hardly affected by the magnetic field. A plausible mechanism by which the spoke spreads to the disk is ionization of neutrals by E×B drift motion of ions. There is a critical gas pressure above which the spoke never spreads to the disk. The reason is considered to be that ions cannot drift in E×B direction above the critical pressure due to a large frictional force between ions and neutrals.