RF sheath two-fluid model with a kinetic electron extension

Radio frequency (RF) sheaths are of fundamental importance in understanding boundary ICRF interactions in fusion devices. A microscale (Debye scale) RF sheath model, considered here, provides an RF sheath admittance boundary condition for global RF wave codes, and the sheath potential for sputtering calculations. In this work an ion-electron two-fluid model is explored where the electron fluid has a kinetic extension. The extension includes the loss of electron charge to the wall from both thermal motion and from directed fluid motion (electron jitter in the RF fields). Particular attention is paid to cases with high frequency RF oscillations (exceeding the inverse electron transit time through the sheath), and oblique or grazing magnetic field lines with respect to the surface. In these cases, the nominal condition for validity of the commonly employed Maxwell-Boltzmann (MB) approximation for electrons often fails, and the model predicts new results for the RF sheath potential and/or RF sheath admittance. The model reduces to the standard MB model in an appropriate limit.