Electrostatic turbulence and transport in a simple magnetized plasma

Gradient driven electrostatic instabilities are investigated in TORPEX [A. Fasoli, B. Labit, M. McGrath, S. H. Müller, M. Podestà, and F. M. Poli, Bull. Am. Phys. Soc. 48, 119 (2003)], a toroidal device (R=1m, a=0.2m) in which plasmas are produced by microwaves (P⩽20kW) with frf=2.45GHz, in the electron cyclotron frequency range. Typical density and temperature are ne⩽1017m−3 and Te≃5eV, respectively. The magnetic field is mainly toroidal (⩽0.1T), with a small vertical component (⩽4mT). Instabilities that can be generally identified as drift-interchange waves are observed and characterized for different levels of collisionality with neutrals. The frequency spectrum and the spatial profile of the fluctuation-induced flux are measured. An 86-tip probe is used to reconstruct the spatio-temporal evolution of density structures across the plasma cross section. The measured structures are characterized statistically, and related quantitative observables are constructed.