Experimental investigation of large-volume PIA plasmas at atmospheric pressure

Large-volume atmospheric-pressure plasmas have been the subject of previous research as a laboratory simulation of ball lightning, but measurements of the plasma properties have been unavailable. The present investigation employed a nonresonant microwave chamber with a 1000-W microwave source operating at 2.45-GHz frequency to produce large volume (up to 0.8 L) plasmas that persisted after microwave shutoff. A Langmuir probe was used to measure electron density and temperature, and the highest values measured were 10(10) cm(-3) at 0.67 eV, respectively. Plasma lifetimes after microwave shutoff were also measured, using both a photocell and a video camera, and were found to average 200 ms. A working hypothesis of the formation of shared electron orbitals in dense gas discharges is put forth to explain this phenomenon.