Experimental and Theoretical Eigenmodes of a Spherical Cavity Partially Filled with Plasma

A complete experimental and theoretical account is given of the eigenmodes (cold and hot) which exist at low power in a cavity partially filled with a plasma. The cavity modes which are perturbed by the plasma together with the basic cold-plasma modes are studied theoretically using uniform cold-plasma theory. The hot-plasma modes of the system are investigated on the basis of a WKB approximation of the relevant equations of a nonuniform hot plasma. Experiments performed with a spherical discharge tube and also with a spherical afterglow plasma give results which are in satisfactory agreement with theoretical predictions. The measured Q factor of the resonances also agrees with theoretical calculations.