Research on modeling of peripheral plasma in a field-reversed configuration

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1) The motion of a plasma ion gyrating around separatrix of a field-reversed configuration (FRC) is studied. Numerical studies showed that the action integral of a particle changes abruptly when a particle passes through the vicinity of a field null Xpoint. This phenomena is understood as collisionless stochastic scattering of the pitch angle. In the case of a particle with positive canonical angular momentum Pe, the resultant correlation coefficients of the action integral between before and after the scattering appear to be stochastic in some cases. In this studies the magnetic flux function inside the separatrix is defined positive. As the action integral increases foe a particle with negative PQ, its motion tends to be adiabatic. If the negative PQ of a particle approaches zero, a stochastic motion is observed. 2) The stable sheath formation in an expanding magnetic field to a divertor plate was studied by a one dimensional analysis. The requirement for flow velocity of ions at a plasma-sheath boundary is more restricted than that of the uniform magnetic field, which should be greater than the ion sound speed. The difference, however, between both cases is an order of the Debye length to plasma radius, which is negligibly small. The requirement for ion flow velocity inside a quasi-neutral plasma was obtained by taking into account the effects of the plasma source. Without plasma source in the quasi-neutral plasma, the ion flow velocity at an injection point should be much greater than the ion sound speed. The ion source inside the quasi-neutral plasma, such as electron impact ionization, considerably mitigates this requirement.