Selfsimilar spacetime evolution of an initial density discontinuity
The spacetime evolution of an initial steplike plasma density variation is studied. We give particular attention to formulate the problem in a way that opens for the possibility of realizing the conditions experimentally. After a short transient time interval of the order of the electron plasma period, the solution is selfsimilar as illustrated by a video where the spacetime evolution is reduced to be a function of the ratio x/t. Solutions of this form are usually found for problems without characteristic length and time scales, in our case the quasineutral limit. By introducing ion collisions with neutrals into the numerical analysis, we introduce a length scale, the collisional mean free path. We study the breakdown of the selfsimilarity of the solution as the mean free path is made shorter than the system length. Analytical results are presented for charge exchange collisions, demonstrating a short time collisionless evolution with an ensuing long time diffusive relaxation of the initial perturbation. For large times, we find a diffusion equation as the limiting analytical form for a chargeexchange collisional plasma, with a diffusion coefficient defined as the square of the ion sound speed divided by the (constant) ion collision frequency. The ionneutral collision frequencymore »
 Authors:

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^{[1]};
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 Department of Physics, University of Oslo, Box 1048 Blindern, N0316 Oslo (Norway)
 Institute of Theoretical Astrophysics, University of Oslo, Box 1029 Blindern, N0315 Oslo (Norway)
 Publication Date:
 OSTI Identifier:
 22227936
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physics of Plasmas; Journal Volume: 20; Journal Issue: 7; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BOLTZMANNVLASOV EQUATION; CHARGE EXCHANGE; COLLISIONAL PLASMA; DIFFUSION; DIFFUSION EQUATIONS; ELECTRON TEMPERATURE; ELECTRONS; ION COLLISIONS; ION TEMPERATURE; MATHEMATICAL SOLUTIONS; MEAN FREE PATH; NUMERICAL ANALYSIS; PLASMA DENSITY; PLASMA SIMULATION; RELAXATION; SOUND WAVES; SPACETIME