title: Chaos healing by separatrix disappearance and quasisingle helicity states of the reversed field pinch.
abstract: The resilience to chaotic perturbations of one-parameter one-degree-of-freedom Hamiltonian dynamics is shown to increase when its corresponding separatrix vanishes due to a saddle-node bifurcation. This is first highlighted for the magnetic chaos related to quasisingle helicity (QSH) states of the reversed field pinch. It provides a rationale for the confinement improvement of helical structures experimentally found for QSH plasmas; such a feature would not be expected from the classical resonance overlap picture as the separatrix disappearance occurs when the amplitude of the dominant mode increases.
authors.affiliation: Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy.
authors.forename: D F
authors.initials: DF
authors.lastname: Escande
authors.forename: R
authors.initials: R
authors.lastname: Paccagnella
authors.forename: S
authors.initials: S
authors.lastname: Cappello
authors.forename: C
authors.initials: C
authors.lastname: Marchetto
authors.forename: F
authors.initials: F
authors.lastname: D'Angelo