title: Improved particle confinement in transition from multiple-helicity to quasi-single-helicity regimes of a reversed-field pinch.
abstract: The quasi-single-helicity (QSH) state of a reversed-field pinch (RFP) plasma is a regime in which the RFP configuration can be sustained by a dynamo produced mainly by a single tearing mode and in which a helical structure with well-defined magnetic flux surfaces arises. In this Letter, we show that spontaneous transitions to the QSH regime enhance the particle confinement. This improvement is originated by the simultaneous and cooperative action of the increase of the magnetic island and the reduction of the magnetic stochasticity.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: L
authors.initials: L
authors.lastname: Frassinetti
authors.forename: I
authors.initials: I
authors.lastname: Predebon
authors.forename: H
authors.initials: H
authors.lastname: Koguchi
authors.forename: Y
authors.initials: Y
authors.lastname: Yagi
authors.forename: Y
authors.initials: Y
authors.lastname: Hirano
authors.forename: H
authors.initials: H
authors.lastname: Sakakita
authors.forename: G
authors.initials: G
authors.lastname: Spizzo
authors.forename: R B
authors.initials: RB
authors.lastname: White