title: Bifurcation to 3D helical magnetic equilibrium in an axisymmetric toroidal device.
abstract: We report the first direct measurement of the internal magnetic field structure associated with a 3D helical equilibrium generated spontaneously in the core of an axisymmetric toroidal plasma containment device. Magnetohydrodynamic equilibrium bifurcation occurs in a reversed-field pinch when the innermost resonant magnetic perturbation grows to a large amplitude, reaching up to 8% of the mean field strength. Magnetic topology evolution is determined by measuring the Faraday effect, revealing that, as the perturbation grows, toroidal symmetry is broken and a helical equilibrium is established.
authors.affiliation: Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA.
authors.forename: W F
authors.initials: WF
authors.lastname: Bergerson
authors.forename: F
authors.initials: F
authors.lastname: Auriemma
authors.forename: B E
authors.initials: BE
authors.lastname: Chapman
authors.forename: W X
authors.initials: WX
authors.lastname: Ding
authors.forename: P
authors.initials: P
authors.lastname: Zanca
authors.forename: D L
authors.initials: DL
authors.lastname: Brower
authors.forename: P
authors.initials: P
authors.lastname: Innocente
authors.forename: L
authors.initials: L
authors.lastname: Lin
authors.forename: R
authors.initials: R
authors.lastname: Lorenzini
authors.forename: E
authors.initials: E
authors.lastname: Martines
authors.forename: B
authors.initials: B
authors.lastname: Momo
authors.forename: J S
authors.initials: JS
authors.lastname: Sarff
authors.forename: D
authors.initials: D
authors.lastname: Terranova