Dynamics of Fast Electrons in an Inhomogeneous Plasma with Plasma Beam Instability

Abstract

The results of numerical simulation of the one-dimensional propagation of fast electrons in a plasma with Langmuir turbulence are presented. The resonant interaction of fast electrons with Langmuir waves and Coulomb collisions with particles of the background plasma are taken into account. It is shown that an increase in plasma density along the direction of the propagation of the electron beam leads to the transformation of the Langmuir turbulence spectrum into a region of high phase velocities and “spreading” of the velocity distribution function of accelerated electrons. For a Gaussian electron beam with an energy of 30 keV at its peak and a characteristic scale of an increase in plasma density of 10⁷ cm, the electron spectrum expands; some of the electrons are accelerated to 1.3 of their initial velocity. In addition, a narrow (~10⁵ cm) layer with an increased turbulence level forms in the plasma. As the electrons move deeper into the plasma, Coulomb collisions restore the inverse over velocity part of the electron distribution function, which leads to the formation of a turbulent layer at a distance from the plasma boundary of ~10⁷ cm–10⁸ cm; however, the energy density of Langmuir turbulence in this layer is ~(10^–6–10^–7) of the plasma thermal energy.