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Theory of rf-driven plasma sheath. (English) Zbl 1181.82062

The properties of a plasma-wall transition layer in the presence of a radio-frequency (rf) electric field are studied theoretically and numerically. Therefore, a collisionless planar sheath in front of an absorbing wall is considered. The frequency of the applied rf field is somewhat below the electron plasma frequency. Thus the electron motion has a high-frequency part, the oscillation in the alternating rf field, and a low-frequency part in which the electrons are accelerated by the electrostatic potential and the ponderomotive force. The ion motion is only determined by the electrostatic potential. The rf oscillations are described by the system of hydroynamic equations for the electron fluid.
Further, a time-stationary model is presented where the coupled Langmuir wave and Poisson system of equations is derived. Solving this system of equations numerically, the profiles of the Langmuir field, the electrostatic potential, and the electron and ion densities are obtained. It is found that in case of an electrostatic potential which is positive at the wall compared to the potential in the bulk plasma, the positive ions are repelled from the wall by the potential, while the electrons are repelled by the ponderomotive force of the rf field. The result is that the plasma is almost completely evacuated at the wall, and is efficiently confined.

MSC:

82D10 Statistical mechanics of plasmas
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