<RESEARCH REPORT>Sheath and Presheath in a Collisionless Open Field Plasma

概要

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The plasma-sheath equation for a collisionless plasma with a finite-temperature particle source in a nonuniform open magnetic field is formulated. The analytic solution of this equation is obtained from the quasi-neutral approximation for the plasma outside the sheath. The potential formed in the plasma depends on the profile of the magnetic field strength; potential drop in the plasma region increases and the ion distribution function becomes wider as the magnetic field strength decreases in the direction of the plasma flow. Application of the generalized Bohm criterion shows that the solution of the plasma equation always satisfies this criterion when the magnetic field monotonically decreases in the outside direction. Comparison of the analytic solution with the numerical results of the plasma-sheath equation confirms that over the whole region except the sheath the analytic solution for various profiles of the magnetic field agrees well with the numerical results when the Debye length is sufficiently small.
核融合科学研究所の論文