Self-organization towards helical states in the Toroidal Pinch Experiment reversed-field pinch

In this paper results of an experimental study of magnetic fluctuations in the Toroidal Pinch Experiment (TPE-RX) [Y. Yagi, S. Sekine, H. Sakakita , Fus. Eng. Design 45, 409 (1999)] are reported. This study has permitted the identification of the experimental conditions under which the usually turbulent spectrum of magnetic fluctuations in TPE-RX turns into a single tearing mode, in the so-called quasi-single helicity (QSH) state. The large data set has allowed us to provide a complete two dimensional map of QSH probability in the current F plane, being F=B-phi(a)/<B-phi>. Two main basins of high QSH probability have been found. The first one, at high current and low \F\, confirms previous results on QSH in other machines; the second one is completely new, and is found at low current and high \F\. These studies show that QSH is a robust, device-independent phenomenon, and a significant step towards a laminar type of dynamo in the reversed-field pinch configuration. (C) 2004 American Institute of Physics.