Introduction

Abstract

A plasma is essentially a gas consisting of charged particles, electrons and ions, rather than neutral atoms or molecules. In general the plasma is electrically neutral overall, but the existence of charged particles means that it can support an electric current and react to electric and magnetic fields. It cannot, however, be treated simply as an ordinary gas which is electrically conducting. There is a very fundamental difference between a neutral gas and a plasma, resulting from the very different nature of the inter-particle forces in the two cases. In the former the forces are very strong, but of short range, so the dynamics of a gas is dominated by two-body, billiard-ball-like collisions. in a plasma the forces are Coulomb forces, which are comparatively weak and of long range. This makes possible a variety of collective effects in a plasma, involving the interaction of a large number of particles, and makes plasma physics a rich and complicated subject.