Trivelpiece-Gould-Modes in an Axial Inhomogeneous Plasma

Experiments on the propagation of TG-modes in a weakly inhomogeneous plasma are reported. The modes travel from the high density part (ω < ω_pe) to that of lower density (ω > ω_pe). The wavelength decreases as expected but an increase of the longitudinal fieldstrength predicted by collisionless theory could not be observed. Two nonlinear effects appear one after another with increasing wave amplitude. These are the sideband instability and a decay into the drift frequency range occuring in the whole plasma column. Neither the region ω ≈ ω_pe nor the very vicinity of the exciter antenna are distinguished. The second instability is accompanied by effective electron heating.