Characteristics of electrostatic ion cyclotron waves in partially ionized plasmas

The characteristics of electrostatic ion cyclotron (EIC) waves in partially ionized plasmas have been investigated theoretically and experimentally. By using a multi-fluid model consisting of plasma and flowing neutral particles, it is found that the modes propagate at frequencies below the ion cyclotron frequency. Moreover, the damping rate of modes could be lower as the ion-neutral collision frequency increases due to the motion of neutral particles in the wave field associated with the plasma-neutral interaction. The finite neutral gas temperature effect is also discussed, and it is found that the unique properties of partially ionized plasmas can be observed in the Earth's ionosphere and low-temperature laboratory plasmas. We will also show experimental results in the HYPER-II device (2.0 m in axial length and 0.30/0.76 m in diameter), in which a partially ionized ECR plasma is produced with a 2.45 GHz microwave. An excitation grid is used to excite the low-frequency plasma fluctuation, and its propagation perpendicular to the magnetic field is measured. Preliminary results obtained with time-resolved laser-induced fluorescence Doppler spectroscopy, developed to discuss neutral dynamics, will also be presented.