Observation of Ion Acoustic Wave by Microwave Scattering Method

An ion acoustic wave in a current carrying plasma is studied by a microwave scattering method. A technique for incoherent scattering of electromagnetic wave of f i =35 GHz by ion acoustic waves of f =20∼70 kHz is described. A dispersion relation and the intensity distribution in k-space of the ion acoustic wave is determined from the angular distribution of the scattered wave. A spatial evolution of the ion acoustic waves along the tube axis is also observed. The observed spatial growth rates are compared with calculated values which take account of both linear and nonlinear growth rates. The linear growth rate thus obtained agrees well with the theoretical value derived for a current carrying plasma, and the value of the nonlinear growth rate is also reasonable when the nonlinear effect is assumed to be due to the ion-trapping.