Rotating plasma discharges of high-pressure molecular vapor using circularly polarized microwaves

We report an experimental demonstration of rotating plasma discharges of diatomic molecular vapor at pressures of a few hundred kPa, i.e., above atmospheric pressure, using circularly polarized microwaves at 2.45 GHz with no external magnetic fields. The active zone of discharges is observed to rotate at frequency of the order of 0.1–20 Hz, which is equivalent to a linear speed of a few cm/s, depending upon the power level, with the same rotation as that of applied circularly polarized microwave fields, regardless of their helicity. The lethargic rotation of the plasma discharges is explained on the basis of ponderomotive force including absorption of the intrinsic angular momentum of the circularly polarized microwaves.