Abstract:
One-dimensional fluid simulation is performed for the unmagnetized plasma consisting of cold
fluid ions and superthermal electrons. Such a plasma system supports the generation of ion
acoustic (IA) waves. A standard Gaussian type perturbation is used in both electron and ion
equilibrium densities to excite the IA waves. The evolutionary profiles of the IA waves are
obtained by varying the superthermal index and the amplitude of the initial perturbation. This
simulation demonstrates that the amplitude of the initial perturbation and the superthermal
index play an important role in determining the time evolution and the characteristics of the
generated IA waves. The initial density perturbation in the system creates charge separation
that drives the finite electrostatic potential in the system. This electrostatic potential later
evolves into the dispersive and nondispersive IA waves in the simulation system. The density
perturbation with the amplitude smaller than 10% of the equilibrium plasma density evolves
into the dispersive IA waves, whereas larger density perturbations evolve into both dispersive
and nondispersive IA waves for lower and higher superthermal index. The dispersive IA waves
are the IA oscillations that propagate with constant ion plasma frequency, whereas the
nondispersive IA waves are the IA solitary pulses (termed as IA solitons in the stability
region) that propagate with the constant wave speed. The characteristics of the stable
nondispersive IA solitons are found to be consistent with the nonlinear fluid theory. To the
best of our knowledge, this is the first fluid simulation study that has considered the
superthermal distributions for the plasma species to model the electrostatic solitary waves.
