A post-processing method to simulate the generalized RF sheath boundary condition

Abstract

Abstract. For applications of ICRF power in fusion devices, control of RF sheath interactions is of great importance. A sheath boundary condition (SBC) was previously developed to provide an effective surface impedance for the interaction of the RF sheath with the waves. The SBC enables the surface power flux and rectified potential energy available for sputtering to be calculated. For legacy codes which cannot easily implement the SBC, or to speed convergence in codes which do implement it, we consider here an approximate method to simulate SBCs by post-processing results obtained using other, e.g. conducting wall, boundary conditions. The basic approximation is that the modifications resulting from the generalized SBC are driven by a fixed incoming wave which could be either a fast wave or a slow wave. The method is illustrated in slab geometry and compared with exact numerical solutions; it is shown to work very well.

Calculation of RF sheath properties from surface wave-fields: a post-processing method

“…This paper generalizes a previous exploratory attempt along these lines, presented in Ref. [34]. That paper was restricted to slow wave polarizations and perpendicular incidence of the magnetic field lines on the surface (hence effectively unmagnetized sheaths).…”

“…In order for the post-processing calculations to be semi-analytical, we assume that the plasma and geometrical parameters are constant on and near the surface. This paper generalizes a previous exploratory attempt along these lines, presented in [34]. That paper was restricted to slow wave polarizations and perpendicular incidence of the magnetic field lines on the surface (hence effectively unmagnetized sheaths).…”

“…A simple analytical example, discussed in [34], is useful for illustrating both the procedure and the power of the method. This example is given for the electrostatic limit in the case of a flat wall with normal vector s=−e x corresponding to j=π/2 in figure 1 and background magnetic field B 0 =B 0 e x .…”

Radio-frequency wave interactions with a plasma sheath in oblique-angle magnetic fields using a sheath impedance model

“…More recently, the generalized RF sheath BC was implemented and tested in rfSOL 19 for the case where the background magnetic field is aligned along the normal vector to surface (the "perpendicular sheath" problem); a numerical solution obtained using this code was also compared with the one obtained by a post-processing method for a high-density plasma, and they were in good agreement with each other. 34 In the present paper, we consider the more general case where the magnetic field is at an oblique angle to the surface. The magnetic field angle affects the wave propagation and boundary interaction as well as explicitly changing the sheath impedance.…”