Modelling electronegative plasmas separated by an internal sheath

It has experimentally been shown that in an ICP with an expanding chamber, adding a small concentration of SF$_6$ to argon can lead to the formation of a stationary double layer [1] separating two plasmas: a high density electropositive plasma in the source, and a low density, high electronegativity plasma downstream. This double layer periodically forms and propagates when increasing the the electronegativity [2]. We present calculation of the discharge equilibrium in the stationary double layer case based on a 1D description of the discharge. The source plasma appears to be only sligthly affected by the downstream plasma. The particles densities downstream are set by the incoming flux of positive ions from the source and attachment ocurring in the downstream volume. Our calculations show fairly good agreement to our experimental data. \newline [1] Plihon \textit{et al.} 2005 \textit{App. Phys. Lett} \textbf{86} 091501 \newline [2] Plihon \textit{et al.} 2005 \textit{J. Appl. Phys.} to be published