Ion and Electron Whistler Wave Dispersion Experiments

Although whistler waves are studied for almost a century, they are still subject of intense research. Laboratory experiments are of particular value for the interpretation of satellite data, which is often ambiguous or at least difficult to understand. The linear plasma experiment VINETA, which is designed to form a large (4.5 m column length, up to 40 cm diameter) and dense (ne ≤ 1019 m-3) plasma with great flexibility in the magnetic field configurations (max. field B0 = 100mT). In the present contribution we discuss investigations on electron whistler waves, right-hand polarised electromagnetic waves in the frequency range ωci << ω ≤ ωce, and ion whistler waves, left-hand polarised electromagnetic waves below the ion cyclotron frequency ω < ωci. Firstly, the dispersion behaviour of electron whistler waves is studied at wavelength up to the plasma dimensions. For smaller wavelengths it turns out that the dispersion relation derived for unbounded whistler waves describes the experimental observations well. For wavelengths greater than the vacuum vessel diameter it is necessary to take the boundary into account. The transition between the two regimes is studied for constant plasma conditions. Secondly, ion whistler waves are considered. In a single-component plasma, the wave dispersion has a real solution only for frequencies below the ion cyclotron frequency ωci. In a multicomponent plasma, the dispersion relation of ion whistler waves exhibit a different behaviour. In an intermediate frequency regime located between the two neighbouring ion cyclotron frequencies, the wave has a maximum group velocity. This feature is used as a diagnostic tool in satellite measurements to determine the ion composition in atmospheric plasmas, but the results have been subject of a scientific debate. Our laboratory study shows first results on ion whistler wave measurements and aims to contribute to clarify the discussed discrepancies