Chaos healing by separatrix disappearance and quasisingle helicity states of the reversed field pinch.
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.
Escande
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Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy.
Paccagnella
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Cappello
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Marchetto
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D'Angelo
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