THE DISPERSION AND MATCHING CHARACTERISTICS OF THE HELICAL RESONATOR PLASMA SOURCE

The dispersion characteristics and the fields of a helical resonator a re obtained. The coil is approximated by a helical current layer with infinite conductivity along the current direction (a ''sheath helix'') . The plasma column is modeled as a cylindrical dielectric in which th e dielectric losses can be neglected in determining the propagation pr operties of the resonator. Assuming the plasma losses are known, the m odel can be used to study the matching of the helical resonator to an external power source which is connected to the helix by a tap. The re sonator is modeled as a parallel connection of two transmission line s egments on each side of the tap position. We determine the efficiency of power transfer to the resonator as a function of the tap position d riving frequency, and plasma loading. We find that whereas for a small plasma loading it is possible to achieve perfect matching, there exis ts a critical value of plasma loading beyond which a perfect match is no longer possible.