Elementary theoretical concepts

Theoretical ideas which were originally developed to explain solar radio bursts have led to a branch of plasma astrophysics which differs in some respects both from laboratory plasma physics and from other theories of astrophysical plasmas. Its main distinguishing feature is the dominating importance which is given to the emission processes, and to the generation and evolution of the Langmuir turbulence which is the direct cause of plasma emission. In introducing theoretical concepts in this chapter emphasis is placed on the theory of waves in plasmas and on the generation of micro-turbulence. (author)