Multiple Ring Discharges in a Cylindrical Resonant Cavity

Observations have been made of an rf multiple-ring discharge which is a variant of the well-known single-ring rf discharge described by J. J. Thomson. A set of discretely-located plasma rings (typically 2 to 5 in number) forms coaxially in the central portion of a cylindrical quartz tube on the axis of a cylindrical cavity excited in the TE011 mode. The rings fit closely inside the inner periphery of the quartz tube at pressures ranging from a few Torr to atmospheric, have a minor diameter of order 1/10 the tube diameter, and are spaced at intervals nearly equal to the tube diameter. Excitation of the degenerate companion TM111 mode results in asymmetrical tilting of the rings. Gas flow through the discharge tube results in a continuous unidirectional axial motion of the rings with new rings being abruptly formed toward the input end of the tube and contracting and vanishing abruptly as they move toward the exit end. A theory is developed which accounts for the observed phenomena.