Turbulent transport in a toroidal magnetized plasma

Turbulent plasma transport due to low-frequency electrostatic fluctuations in a toroidal plasma is studied experimentally. The data are obtained in a magnetized toroidal plasma with no toroidal transform. The plasma is generated by a discharge from a hot electron emitting filament and diagnosed by conventional Langmuir probes measuring densities by electron or ion saturation currents and floating potentials. We present results for the statistical properties of the fluctuating radial transport caused by low-frequency electrostatic turbulence in the device. The turbulent plasma flux is identified as the product of the fluctuating density and the E × B/B2-velocity. Even though the probability densities of the fluctuating electric fields and plasma densities are close to Gaussians, we find strongly intermittent features in the flux signal obtained as the product of these two fluctuating quantities. A conditional statistical analysis gives insight in detail of the turbulent transport. The intermittency studies are extended by analyzing the excess statistics, i.e. the average duration of time intervals in the flux signal spent above a given reference level. We find that this analysis offers a very effective measure for intermittency effects. In our case, the signal is characterized by an excess of temporally narrow, large amplitude bursts, when compared with an equivalent Gaussian random signal. (paper)