Comparative experimental study of coherent structures in a simple magnetized torus

This paper reports a comparative experimental study of large-scale coherent structures which are embedded in the turbulent fluctuations observed in a magnetized plasma device. The confining magnetic field is purely toroidal a nd has no rotational transform. Turbulent density fluctuations of two diffe rent plasma discharges are compared: thermionic discharge and inductive res onant wave heating. It turns out that fundamental features of spatiotempora l structures depend primarily on the plasma source and not on the magnetic field configuration. In the thermionic discharge plasma double-vortex struc tures and in the wave-heated plasma single-vortex structures are found. Thi s can be attributed to the injection of mass and negative space charge in t he case of thermionic discharge. The phase coherency is determined by the l arge-scale coherent structures. Phase shift of approximate to pi /2 between plasma potential and density structures changes in sign for the two differ ent plasma sources.