Collisionless plasma expansion into a vacuum
Abstract
Particle simulations of the expansion of a collisionless plasma into vacuum are presented. The cases of a singleelectrontemperature plasma and of a twoelectrontemperature plasma are considered. The results confirm the existence of an ion front and verify the general features of selfsimilar solutions behind this front. A cold electron front is clearly observed in the twoelectrontemperatures case. The computations also show that for a finite electrontoion mass ratio, m_{e}/m_{i}, the electron thermal velocity in the expansion region is not constant, but decreases approximately linearly with ξ=x/t, where x is distance and t is time. A selfsimilar solution, derived from the relation T_{e}n^{1γ}_{e}=const, where T_{e} is the electron temperature, n_{e} is the electron density, and γ is a constant (instead of the isothermal assumption made in earlier theories), yields a linearly decreasing ion acoustic speed, c≃c_{0}(γ1) ξ/2, and comparison with computer simulation results show that the constant γ1 is proportional to (Zm_{e}/m_{i})^{1/2}, where Z is the ion charge number.
 Publication:

Physics of Fluids
 Pub Date:
 July 1979
 DOI:
 10.1063/1.862751
 Bibcode:
 1979PhFl...22.1384D
 Keywords:

 Collisionless Plasmas;
 Computerized Simulation;
 Electron Energy;
 Plasma Dynamics;
 Vacuum Effects;
 Electron Density Profiles;
 Electron Plasma;
 Energy Technology;
 Expansion;
 Ion Acoustic Waves;
 Ion Distribution;
 Laser Fusion;
 Mass Ratios;
 Vlasov Equations;
 Plasma Physics