Introduction

During the past few decades, plasma physics has become established as a major research field. As a result, the field includes a very substantial body of knowledge covering a wide variety of branches, from the most theoretical to the most practical, comparable to any other subdiscipline of physics. As with any other science, progress has been made most effectively when an early quantitative confrontation between theory and experiment has been possible. This confrontation places strong demands upon theory to do calculations in realistic configurations and circumstances, but it also requires that the properties of plasmas be measured experimentally as completely and accurately as possible. For this reason much of the effort in experimental plasma physics is devoted to devising, developing, and proving techniques for diagnosing the properties of plasmas: plasma diagnostics.

A major driving force behind the research on plasmas has been, and still is, the prospect of generating economically significant amounts of power from controlled thermonuclear fusion. Fusion has its own imperatives of temperature, density, confinement, and so on, which provide a stimulating and relevant environment in which plasma research is conducted. Moreover, the vitally important diagnosis of fusion plasmas poses problems that are often enhanced by the nature of the fusion goal. For example, the high temperatures sought for fusion frequently eliminate the possibility of internal diagnosis by material probes.

The overall objective of plasma diagnostics is to deduce information about the state of the plasma from practical observations of physical processes and their effects.