Oscillations and Waves in Plasmas

Abstract

Various kinds of oscillations and waves can be excited in a plasma. In other words a plasma has a large number of oscillatory degrees of freedom. As a rule, oscillatory processes which start in one place propagate in space from that point. A propagating oscillation of this kind is called a wave. Oscillatory processes are characterized by three basic quantities: the amplitude, i.e., the height of the oscillation; the frequency, i.e., the number of oscillation cycles per unit time; and the phase, i.e., the time at which the cycle passes through a characteristic point (maximum, minimum, etc.). The amplitude and the frequency are absolute quantities: They characterize a given oscillatory process as such and not in comparison with other processes. The phase is a relative quantity; it is arbitrary in itself and has meaning only in terms of the phase difference between two oscillatory processes.