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 et al., 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
5Bf(a)/^Bf&. Two main basins of high QSH probability have been found. The first one, at high
current and low uFu, 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. © 2004 American Institute of Physics.