Visible Plasma Clouds With an Externally Excited Spherical Porous Cavity Resonator

A microwave driven resonator is as an electron/ion cloud generator for illumination and plasma source applications. A sustained porous cavity resonator (PCR) glow discharge is externally excited using a resonant frequency electromagnetic (EM) wave that excites large internal electric fields. The resonator with a Q of 300 amplifies the incident electric field by factors of about 100 causing a breakdown of the neutral gas inside the sphere. The rise time of the fields inside the sphere is Q times the wave period. A glowing plasma ball is sustained around the point where the maximum electric fields exceed the plasma-discharge threshold for the low-pressure gas inside the resonator. After the EM pump field is removed, the plasma light source is rapidly quenched. The externally driven spherical PCR was fabricated from a theoretical design of the PCR for a laboratory demonstration of the plasma ball generation system. Using both theory and experiment, basic research has been applied to understand: 1) the EMs of resonator excitation and amplification; 2) the generation of light by glow radio frequency discharge; and 3) the effect of background neutral density of the size and intensity of the glowing plasma clouds. For this study, plasma resonators were constructed for the spherical TM101 and TE101 modes and a TE011 circular-cylindrical cavity. All PCR structures provide the ability to confine a plasma into a desired spatial shape without magnetic fields.