Basic turbulence studies on TORPEX and challenges in the theory-experiment comparison

TORPEX [A. Fasoli, B. Labit, M. McGrath, S. H. Muller, M. Podesta, and F. M. Poli, Bull. Am. Phys. Soc. 48, 119 (2003)] is dedicated to the study of electrostatic instabilities, turbulence, and transport. Plasmas are produced by waves in the electron cyclotron frequency range and are confined by a toroidal magnetic field of about 0.1 T to which a small vertical component B-z is added. The crucial role of B-z for the basic confinement scheme through the generation of parallel flows has been studied previously. This paper focuses on the effects of B-z on turbulence. The observed strong dependence indicates an intrinsic coupling between average profiles, confinement, and turbulence regulated by the action of B-z. Two approaches to characterize turbulence are adopted, via time series statistics and via the direct measurement of spatiotemporal structures, made possible by the novel hexagonal turbulence imaging probe diagnostic, which is described in detail. Analysis methods to condense the large amount of data of such imaging diagnostics are proposed. (C) 2005 American Institute of Physics.