Propagation of electromagnetic waves along an annular plasma column

Historically, surface wave sustained microwave plasmas were almost exclusively generated and investigated in a standard configuration of an elongated cylinder. One of the new configurations, proposed more recently, is Duo-plasmaline [1]. There, the plasma is located outside a cylindrical dielectric vessel, adjacent to its wall, and forms a structure of a ring shaped cross-section. An axially located cylindrical conductor corresponds to the outer metallic cylinder surrounding plasma in the standard configuration. We report results of a numerical analysis of wave propagation in such annular structures in a wide range of plasma parameters. We show that two different waves may propagate, each related to one of the two boundary surfaces of the plasma. The waves can be clearly distinguished in the domain of large electron densities. Presented are calculated complex propagation coefficients of waves and radial distributions of the electromagnetic field. Asymptotic cases are defined and analyzed.