Abstract:
Space plasmas provide abundant evidence of a highly energetic particle population that results in a
long-tailed non-Maxwellian distribution. Such plasmas can be effectively modeled with kappa distribution.
The superthermal population in the tail of kappa distribution can have significant effects
on the wave dynamical processes. We perform the fluid simulations to examine the effects of superthermal
populations on the breaking of the electrostatic ion-acoustic (IA) wave, which is the most
fundamental mode, existing in the unmagnetized plasmas. We construct a fluid model for exciting
IA waves by employing a kappa distribution function for the superthermal population of electrons
along with inertial cold ions (protons). We focused on the nonlinear excitations; in the form of ion
acoustic solitary wave (IASW) structures formed through the process of wave breaking, and investigated
the role of superthermal electron population in the initiation of the steepening, wave breaking,
and propagation characteristics of the IASWs in plasma. From the output of the simulation, we
established the criteria for the steepening time based on the variations in the phase velocity of the
IASWs. Furthermore, we examined the maximum ponderomotive potential and ponderomotive
frequency during the wave breaking process. We found that the time corresponding to the peak
in the maximum ponderomotive potential is the time of the initialization of the wave breaking
process. We present a detailed investigation of the role of the ponderomotive forces acting on the
plasma at each time step, which explains the physics of the wave breaking in nonthermal plasmas.
