This paper reports a comparative experimental study of large-scalecoherent structures which are embedded in the turbulent fluctuationsobserved in a magnetized plasma device. The confining magnetic fieldis purely toroidal and has no rotational transform. Turbulentdensity fluctuations of two different plasma discharges arecompared: thermionic discharge and inductive resonant wave heating.It turns out that fundamental features of spatiotemporal structuresdepend primarily on the plasma source and not on the magnetic fieldconfiguration. In the thermionic discharge plasma double-vortexstructures and in the wave-heated plasma single-vortex structuresare found. This can be attributed to the injection of mass andnegative space charge in the case of thermionic discharge. The phasecoherency is determined by the large-scale coherent structures.Phase shift of ≈π/2 between plasma potential and densitystructures changes in sign for the two different plasma sources.
Fluid theory and simulations of instabilities, turbulent transport and coherent structures in partially-magnetized plasmas of discharges