Interaction between Plasma Flow and a Magnetic Barrier : Shock Formation

概要

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A time-dependent plasma flow compatible with most of the experiments involving a plasma gun working in a high density regime is considered. Shock development is due mainly to evolution of the flow parameters. A simplified one-dimensional shock model is used and the plasma is assumed not to perturb very much the vacuum magnetic field. Only sub-Alfven flow velocities are allowed so that only a gasdynamic shock can develop. Calculation around the sonic transition in the barrier shows that except for a very fast increase of density, the distribution of pressure can produce backward facing sound waves in the flow. The pressure gradient is strong and the sound waves converge quickly close to the sonic point. If the ion-ion collision time is smaller than the converging time, then no Landau damping occurs and a shock can develop. If the ion-ion collision time is larger than this converging time, assuming collision free trajectories for ion, the pressure gradient becomes weak and no clear shock is expected. The optimum condition for shock formation has a simple formulation and is given but the distinction between conditions with and without a shock depends on each experiment and has no simple expression; for that problem a graphical method is necessary.
核融合科学研究所の論文