Boundary Effects for Diffusion of a Plasma Streaming along a Uniform Magnetic Field

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Effects of conducting boundary walls for a plasma are investigated by applying external potentials to their walls. The plasma is streaming almost without collisions for neutral particles along a uniform magnetic field, and through each center hole of an upper or a lower end wall along the plasma stream. A diffusional radial region across the magnetic field is divided into three parts; the first region near the plasma center where the plasma potential hardly depends on the boundary potentials, the second region depending on two end walls potential, and the third region depending on a side wall potential. In the first or second region, each diffusion coefficient is very near the ion free diffusion coeffcient with B^<-2>, while it hardly depends on B in the third region. An external negative potential applied to two end walls is very effective for the plasma potential drop, which produces an enhanced diffusion region between the first and the second region. Moreover, in the second region, the electron current component towards the upper end wall from the lower is larger than that towards the lower, which means a reflection of electrons. If the plasma becomes collisional with an increase of pressure, all the external potentials cease to drop the plasma potential because of sheath effects while the electron components towards the upper become less everywhere. Therefore, that a plasma is free streaming, is essential for a penetration of external electric field and reflections of electrons on the end walls along the magnetic field which lead to an ion diffusion. Then, the transeverse electric field term determined experimentally is neglisible compared with that diffusion term in the diffusion equation.
核融合科学研究所の論文

Boundary Effects for Diffusion of a Plasma Streaming along a Uniform Magnetic Field

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