PROPAGATION OF RF-INDUCED DENSITY DEPRESSIONS

In a collisionless magnetized argon plasma, a density cavity is produc ed by the ponderomotive force that the transient radiation field of a converging resonance cone exerts on the plasma. After the radiation fi eld has decayed, the cavity develops into isotropic rarefactive densit y waves that propagate at the ion sound velocity in the plasma. Since the main density hole is well separated from the exciting structure, t he propagation is not disturbed by the exciter antenna. The shape of t he solitary density waves is determined by the opening angle of the co ne and can, in a linear approximation, be described by a simple 3d wav e equation. The propagation is apparently independent of the magnetic field. Nonlinear features of wave propagation were studied by superimp osing counterpropagating waves. A model for the spatio-temporal evolut ion is presented.