ELECTRON-CYCLOTRON WAVE SCATTERING BY A PROBE LAUNCHED ION-ACOUSTIC-WAVE

Electromagnetic wave scattering in a plasma half-space from a propagat ing ion acoustic wave density perturbation with a transverse conductin g boundary condition is analyzed. The analysis shows that there are tw o different types of scattered waves. One propagates only in the regio n where the plasma density is perturbed, its frequency and wave vector satisfies the conditions for a three-wave interaction process. The ot her propagates as an unperturbed electron cyclotron mode with either a n upshifted or downshifted frequency. Experiments are performed to exa mine electron cyclotron wave scattering by an ion acoustic wave excite d by means of a grid along the magnetic field line in a mirror machine . The backscattered waves propagating away from the density perturbati on region are measured and their dependence on the ion acoustic wavele ngth is examined. The scattered wave in the region of ion acoustic wav e propagation is examined by measuring the scattered wave field patter n when the ion acoustic wave number is much larger than that of the in cident wave. The measurements demonstrate that the scattered waves ind eed propagate as two different modes.