Flying plasma disks in basalt microwave furnace

Our experiments study microwave heating phenomena of small basalt stones (∼10 cm³) in a rectangular cavity (WR340) powered by a 650 W, 2.45 GHz magnetron. Occasionally, we observe the creation of a silvery cloud of plasma, in a disk shape. This occurs first on the top of the basalt stone. Then, the plasma ring (of 2-3 cm diameter) is flying about 20 cm from the stone along the cavity to the magnetron antenna, where it disappears. Soon after, another plasma ring is generated near the stone, flies to the magnetron, and repeatedly. The repetition period and the flying disk life cycle are approximately 1 sec. The effect is accompanied by a unique sound, and it ceases after 15-20 sec of heating when ordinary heating effects occur. We interpret the flying disks as plasmoids produced by a nonlinear interaction of non-stationary standing microwaves with the stone's surface. The paper discusses this effect in view of Kapitza's idea on spherical plasmoids (lighting fireballs) generated by intensive standing radio-waves, in atmosphere and in laboratory experiments. Astrophysics and geophysics effects related to our observation are discussed as well.