Eigenvalues of a Microwave-Cavity-Lossy-Plasma System

Abstract

A cylindrical microwave cavity containing a concentric plasma column can be resonated in an infinite number of electromagnetic wave modes. The resonances all shift upward towards coaxial cavity modes as the electron density in the plasma is increased if collisions are neglected. The characteristic eigenvalue equation for all modes including collisional effects is derived and typical graphs for fundamental modes are presented. The solutions of the eigenvalue equation can be explained on the basis of coupled-mode theory. The empty cavity mode and the coaxial (infinite electron density) mode which are originally overcoupled, uncouple from each other for sufficiently large values of electron collision frequency. The imaginary part of the roots, which is inversely proportional to the Q of the plasma cavity system, shows the two modes distinctly.