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Abstract
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Exact analytical self-similar solution is presented for free collisionless expansion of a two-component
plasma of inertial ions and nonextensive electrons into vacuum, using the generalized nonextensive
velocity distribution for electrons. Furthermore, a hydrodynamic model of plasma expansion in the
presence of the ambipolar diffusion caused by collisions among the plasma species, such as electrons
and ions, is developed and a Fokker-Planck-like generalized diffusion equation for steady-state
expansion of a nonextensive electron-ion plasma is derived. For the case of generalized statistics and
in the absence of particle diffusion, the density, velocity, electric potential, and field of expansion
profiles are exactly obtained and studied in terms of the self-similar parameter. It is found that
superthermal electrons lead to an accelerated expansion of plasma compared to that of Maxwellian
electrons. It is also revealed that the nonextensivity parameter plays a fundamental role on the
density, velocity, electric potential, and field configuration of the expansion. Therefore, one is able to
distinguish three different regimes q < 1, q ¼ 1, and q > 1 for expansion corresponding to subnonextensive, extensive, and super-nonextensive statistical profiles for electrons, respectively.
Current research can provide useful information and suggests techniques for investigation of the
involved statistical mechanism on the role of the energetic electron fluid in the expansion of plasma
in strong pulsed laser-matter interaction experiments. It is also shown that the particle diffusion
expansion mechanism becomes more dominant for relatively large values of the nonextensivity
parameter, q.
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