title: A dynamic magnetic tension force as the cause of failed solar eruptions.
abstract: Coronal mass ejections are solar eruptions driven by a sudden release of magnetic energy stored in the Sun's corona. In many cases, this magnetic energy is stored in long-lived, arched structures called magnetic flux ropes. When a flux rope destabilizes, it can either erupt and produce a coronal mass ejection or fail and collapse back towards the Sun. The prevailing belief is that the outcome of a given event is determined by a magnetohydrodynamic force imbalance called the torus instability. This belief is challenged, however, by observations indicating that torus-unstable flux ropes sometimes fail to erupt. This contradiction has not yet been resolved because of a lack of coronal magnetic field measurements and the limitations of idealized numerical modelling. Here we report the results of a laboratory experiment that reveal a previously unknown eruption criterion below which torus-unstable flux ropes fail to erupt. We find that such 'failed torus' events occur when the guide magnetic field (that is, the ambient field that runs toroidally along the flux rope) is strong enough to prevent the flux rope from kinking. Under these conditions, the guide field interacts with electric currents in the flux rope to produce a dynamic toroidal field tension force that halts the eruption. This magnetic tension force is missing from existing eruption models, which is why such models cannot explain or predict failed torus events.
authors.affiliation: Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA.|Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: Clayton E
authors.initials: CE
authors.lastname: Myers
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Yamada
authors.affiliation: Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA.|Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.|Laboratory for Space Environment and Physical Sciences, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China.
authors.forename: Hantao
authors.initials: H
authors.lastname: Ji
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: Jongsoo
authors.initials: J
authors.lastname: Yoo
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: William
authors.initials: W
authors.lastname: Fox
authors.affiliation: Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA.|Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Jara-Almonte
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA.
authors.forename: Antonia
authors.initials: A
authors.lastname: Savcheva
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA.
authors.forename: Edward E
authors.initials: EE
authors.lastname: DeLuca