Published online by Cambridge University Press: 13 March 2009
A specific type of longitudinal wave instability in a plasma due entirely to an external quasi-static electric field E0 is considered for the cases of ion-acoustic and Langmuir waves. The quasi-static time variation of the field leads to a relatively simple mechanism for the development of instability. For frequency ranges typical of ion-acoustic and Langmuir waves dispersion relations are obtained, with Landau damping and pair Coulomb collisions taken into account in addition to E0. The model integral of Bhatnagar, Gross & Krook is used to describe collisions. Two methods for taking account of the influence of the electric field on development of the instability are compared: that of Pines & Schrieffer and that of Brinca and Dysthe. Expressions are obtained for the growth rates in the framework of linear theory. Numerical simulations of both types of instabilities are performed for specific values of the plasma parameters.