Propagating structures in drift-wave turbulence

The formation and propagation of spatio-temporal fluctuation structures in drift-wave turbulence in a linearly magnetized helicon device is investigated. Structures are extracted by correlation analysis. Their typical lifetime exceeds the eddy turnover time by one order of magnitude. The radial correlation analysis yields radial propagation of turbulent fluctuations with velocities up to 50% of the ion sound speed. The two-dimensional analysis of the entire azimuthal cross-sections reveals that the propagation is purely azimuthal and that the radial speeds are an artefact of the one-dimensional measurement of a multi-dimensional propagation