Ion energy spectrum in expansion of plasmas with nonextensive electrons

Abstract

The collisionless expansion of plasma with cold ions and nonextensive distributed electrons into vacuum is investigated using a self-similar hydrodynamic model in both planar and nonplanar geometries. The speed, size and the energy spectrum of ions in expanding plasma is studied in terms of nonextensivity and geometry parameters. It is found that superthermal electrons with nonextensive distribution accelerate ions to higher speeds and creating a high energy tail in ion-energy spectrum compared to that with Maxwellian electrons. The later may be useful in describing the high energy ions created in irregular space plasma expansion or strong intense laser-plasma accelerated expansion. A generalized Fokker-Planck like diffusion equation is obtained for plasmas with q-nonextensive electrons applicable to different geometry of expansion. From numerical investigation, it is observed that the rates of diffusive expansion for nonplanar geometries are different from planar ones. The anomalous character of diffusive plasma expansion is studied and concluded that three distinct regimes depending on the q-parameter value exists in all geometries. Keywords: Plasma expansion, Nonextensive electrons, Ion energy spectrum, Self-similar, Nonplanar geometries