Nonlinear behaviour of a finite amplitude electron plasma wave, III. The sideband instability

Abstract

Computations of the evolution of the electron distribution function in a plasma subsequent to the excitation of a constant finite amplitude electron plasma wave show that the system is stable for plasma parameters for which under experimental conditions the sideband instability is found to be excited. When the time (or space) variation of wave amplitude is included a group of particles initially trapped is detrapped and then behaves like an electron beam passing through the plasma. The experimental dispersion of test waves in a low density plasma is compared with theoretical predictions for parameters given by the detrapping model. Further, measurements of the electron distribution function in the presence of a finite amplitude wave as a function of position, wave amplitude, and wave frequency, show features which are consistent only with a detrapped beam.

Electron plasma waves and plasma resonances

“…However the situation had been transformed in 1963 when Malmberg and Wharton [9] reported results on a specially designed uniform plasma verifying the essential features of Landau's theory. Their work was later confirmed in the 1970s and extended in a series of papers by Franklin et al [10][11][12][13]. However that work was done with plasmas generated in so-called Q(quiescent plasma)-machines with the plasmas magnetically confined, electrons generated thermionically, and ions produced by a surface ionization mechanism.…”

“…A literature search today relating to Langmuir waves leads into the field of turbulence in plasmas, particularly associated with fusion plasmas. Initially in the references already given above [10][11][12][13], interest was in deviation from so-called linear Landau damping. The process of the nonlinear transfer of energy out of electron plasma waves by the generation of other waves of a lower frequency is often also referred to as wave decay.…”