Collisions in the electrostatic weak turbulence theory: A possible connection with the ubiquity of suprathermal velocity distributions in space plasmas

The weak turbulence theory is a valuable theoretical tool for the analysis of nonlinear, kinetic instabilities in collisionless plasmas. However, the long-lasting timescale of nonlinear processes suggests that collisions might affect the late plasma dynamics, acting alongside oscillatory effects. These intermediate situations, where collective and collisional processes coexist in the plasma dynamics, have been rigorously formulated only recently. One of the outcomes of this extended weak turbulence theory is a new term in the kinetic equation for waves, which depicts the emission of electrostatic fluctuations, in the eigenmode frequency range, caused by particle scattering. This electrostatic form of “braking radiation”, named “electrostatic bremsstrahlung”, is capable of altering the corresponding wave-spectrum, which will then modify the velocity distribution function through wave-particle resonance. In this talk, I will present the first numerical analysis of the time evolution of the electrostatic bremsstrahlung emission in the Langmuir wave range and its subsequent impact on the shape of the electron velocity distribution, like the scattering of a small fraction of the core population to suprathermal velocities range, even in the presence of binary collisions.