Propagation and damping characteristics of low-frequency waves in field-reversed configuration plasmas

Propagation and damping properties of low-frequency waves in extremely high beta plasmas have been investigated in the field-reversed configuration plasma injection experiment apparatus. Two distinct wave modes were excited by different antenna geometry and the radial structures of their magnetic components were measured in detail. Due to the high beta nature of the plasma, the Alfven resonance predicted for the cold plasma vanished and the wave with small parallel wave number k(z)similar to 2.5 m(-1) propagated in a broad area across the separatrix. The wave exhibited moderate dissipation, which was suggestive of the resistive damping. The wave with large parallel wave number k(z)similar to 7.0 m(-1), however, underwent quite strong damping inside the separatrix. Transit-time magnetic pumping, which converts the wave energy to the ion parallel kinetic energy, is most likely to be responsible for this strong damping since the wave's parallel phase velocity is close to the ion thermal velocity. (C) 2007 American Institute of Physics.