Kinetic description of the neutral sheath

The interaction between plasma and wall is a topic of continuous interest. The cold neutral particles coming from the wall have a great influence on the energy balance of the plasma. Also the fast neutral atoms created by charge exchange on the plasma represent the ion energy distribution. In contrast to our earlier work the kinetic description of the neutral sheath has now been extended to inhomogeneous plasma parameters and cylindrical coordinates. The calculation of the neutral sheath start from the Boltzmann equation and an integral equation for the neutral density is derived. These calculations are done in plane and cylindrical coordinates and the integral equation is solved numerically. In addition to the neutral density the distribution-function is calculated. The relationship between these functions which are measured in plasma experiments and plasma density and temperature is examined. The approximate solution shows that the usual procedure for obtaining the ion temperature (from a plot of the logarithm of the distribution function, versus energy) is valid only if the neutral density is constant. In larger experiments where the neutral sheath is small the ion temperature should be obtained from a plot of the flux function of outgoing neutrals versus energy. (orig.)