Mass motion and heating in a magnetic neutral point system

Abstract

We present optical spectroscopic and magnetic probe observations of a laboratory discharge device, in which magnetic field line reconnexion occurs at an x−type neutral point. Time-resolved spectral-line profiles of the ionized argon line A II λ4348 are presented. These allow the determination of Doppler shifts and broadenings near the neutral point. Plasma heating occurs at the neutral point and downstream from it. Plasma is ejected from the downstream sides of the neutral point region at the local Alfvén speed at all times. This is equal to about one-tenth the upstream Alfvén speed at the one time it is known. The downstream magnetic Mach number or ‘local reconnexion rate’ is found to be nearly independent of the plasma conductivity and time. The rate of transfer of magnetic flux from the upstream to downstream regions is strongly dependent on conductivity and time.