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AbstractAbstract
[en] The sheath formed between a magnetized plasma and a particle absorbing wall is examined for the case in which the magnetic field intercepts the wall at a small angle 0 degree <ε approx-lt 9 degree, where sin ε=B·n/|B|, and n is the unit normal to the wall. The model is time-independent and one-dimensional (1-D) with all functions varying only in the direction normal to the wall. The ions are modeled by a Maxwellian velocity distribution which is modified by the condition that ions, which would have hit the wall, are absent. For the electrons a fluid description is used, including the effects of electron--neutral collisions. The transport of particles due to turbulent electrostatic fluctuations is modeled by a constant electric field perpendicular to both B and n. It is found that in the range of angles under consideration, there are two distinct regimes of sheath formation. If ε approx-lt bar ν=ν/Ωe (grazing incidence), where ν is the electron--neutral collision frequency and Ωe is the electron cyclotron frequency, then the properties of the sheath are determined by a parameter λ which is the ratio of the convective (ExB) and diffusive electron flows. If λ approx-lt 1, the wall potential is negative and the sheath scale length is on the order of an ion gyroradius. If λ approx-gt 1, the wall potential is positive and, for large λ, the sheath is characterized by two scales: a short length, which is a decreasing function of λ, adjacent to the wall, and the ion gyroradius farther from the wall. For ε much-gt bar ν, (oblique incidence) the potential at the wall is negative with a magnitude close to that of the unmagnetized plasma and is only weakly dependent on ε
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