The Washimi and Karpman ponderomotive interaction due to electron wave propagation is investigated for low-temperature unmagnetized plasmas described by an isotropic kappa distribution. We perform a brief analysis of the influence of the kappa distribution in the dispersion relations for a low-temperature plasma expansion at the lowest order in which the thermal effects are appreciable without considering the damping characteristics of the wave. The spatial and temporal factors of the ponderomotive force are obtained as a function of the wavenumber, the spectral index κ and the ratio between the plasma thermal velocity and the speed of light. Our results show that for unmagnetized plasmas non-thermal effects are negligible due to the spatial ponderomotive force when non-relativistic thermal velocities are considered. However, for unmagnetized plasmas, the temporal factor of the ponderomotive force appears only due to the presence of suprathermal particles, with a clear dependence on the κ index. We also analyze the role of the non-thermal effect in the induced Washimi and Karpman ponderomotive magnetization and the total power radiated associated with it. Furthermore, we show that the magnitude of the slowly varying induced ponderomotive magnetic field increases as the plasma moves away from thermal equilibrium.
Competition between ponderomotive and thermal forces in short-scale-length laser plasmas