On parametric excitation of high-frequency potential waves in a cold homogeneous plasma

Parametric instability of potential waves has been investigated in a cold homogeneous plasma, when in the wave excitation field electrons may gain relativistic velocities. Equation is obtained, which describes parametric wave excitation without any limits on the amplitude of the external wave field. The criterion for the usage of parametric equations, which do not take into account relativistic effect, has been found. The dependence of increment excited as a result of relativistic changes in the electron mass, on the wave vector is obtained