Experimental study of low-frequency electrostatic fluctuations in a magnetized toroidal plasma

An experimental study of low-frequency electrostatic fluctuations is presented for a plasma produced by a steady-state discharge in a magnetized toroidal plasma device without a rotational transform. A significant intermittency of the fluctuations is observed. Thus the evolution and propagation of large coherent vortical structures is demonstrated by a conditional sampling technique. The flutelike nature of the structures is explicitly demonstrated. The analysis includes measurements of fluctuations in plasma density, electric potential, and electron temperature. The relevance of the observations to anomalous transport in the device is pointed out. The performance of the conditional sampling technique is compared to a simple correlation analysis by a Monte Carlo simulation.