AXIAL STRUCTURE OF A SHIELDED PLASMA-COLUMN SUSTAINED BY A DIPOLAR ELECTROMAGNETIC-WAVE

We consider a low-pressure plasma column contained in a dielectric tube surrounded by vacuum and shielded by a metal enclosure. The plasma is sustained by a travelling, weakly damped electromagnetic dipolar wave. The metal shielding turns out to influence substantially the dispersion characteristics and hence the axial structure of the discharge in contrast to the case of azimuthally symmetric waves. Axial profiles of the electron number density and wave power have been calculated. A comparison with the available experimental data shows the significance of the non-uniform radial plasma density profile for this configuration, which is taken into account by replacing the actual electron-neutral collision frequency for momentum transfer by a greater effective value. It is determined by applying a scaling procedure (which is not a curve fitting) that refers to a single experimental point. Thus a very good agreement between theory and experiment has been obtained.