Measurements of Ion Energization by a Pair of Beating Electrostatic Ion Cyclotron Waves

An experimental study of ion heating by beating electrostatic ion cyclotron (EIC) waves in a magnetized, rf-sustained plasma has been performed in order to explore an ion acceleration mechanism that was predicted theoretically. Ion heating up to 35 % was observed in the presence of electrostatic waves excited by a two-plate antenna. It was found that ion-neutral collisions significantly alter dispersion properties of the backward branch of the EIC wave. In addition, it was shown that beating waves can heat ions to higher temperature than a single electrostatic wave. This enhancement in ion temperature was found to be 15 % for the particular conditions of the reported experiment, but is expected to be significantly higher in a less collisional plasma. This finding supports theoretical prediction that beating waves can produce more efficient heating by interacting with ions below the single-wave velocity threshold. Nomenclature v = velocity vti = ion thermal velocity ω = wave frequency f0 = zero order particle velocity distribution function f1 = first order particle velocity distribution functio