Numerical and experimental observation of three-dimensional null-point magnetic reconnection and subsequent dynamical relaxation

We have obtained the first complimentary numerical simulation and experimental observation of three-dimensional (3D) null-point magnetic reconnection and subsequent dynamical relaxation to a 3D helical Taylor state. The reconnection and relaxation processes have been observed in the context of two interacting co-helicity spheromaks constrained by a cylindrical flux conserver and oriented in such a way as to form an isolated magnetic field null point at its center. Fast null-point reconnection, facilitated by simultaneous tilting of the spheromaks, is observed to proceed as the null-point itself escapes radially outward from the flux conserver. This is followed by slower component reconnection leading to the 3D relaxed helical Taylor state. We further show that during the fast reconnection phase, the location of most intense reconnection is observed to be co-located with the magnetic null, while the direction of the propagation of the null is prescribed by the reconnecting magnetic fields that surround it. Unlike many previous (quasi)-periodic 3D reconnection studies, we observe no persistent two-dimensional current channel in this system. These findings, obtained numerically and confirmed by pre-existing but heretofore unexplained experimental data, directly contribute to our understanding of magnetic reconnection in non-periodic space and astrophysical plasmas, as well as demonstrate the synergy of a close collaboration between computational and laboratory plasma physics in the study of a universal natural phenomenon. The new multi-fluid implicit spectral element code HiFi, developed at PSI-Center (University of Washington), was used for the numerical simulations, while the experiment was conducted at the Swarthmore Spheromak Experiment. Streamlines of magnetic field in the localized 3D reconnection region, with arrows indicating the direction and magnitude of plasma flow, forming focused Alfvenic jets pointing outward from the reconnection region.