Experimental study of the reconnection process

Abstract

We briefly review the results of a laboratory field-line reconnection experiment. In doing so the flux transfer rate is defined and contrasted with magnetic Mach numbers as measures of the reconnection rate. We examine the origin of the reconnection electric field to determine some of the requirements of nonsteady versus steady reconnection. The. dependence of various measures of the reconnection rate on electrical conductivity is discussed as well as some experimental features which may relate to previous theory. Finally, we present some approximate scaling between laboratory events and the geomagnetic substorm. We reach three major conclusions: (a) The flux transfer rate as a measure of the reconnection rate is different from a magnetic Mach number. (b) The early reconnection process is quasi-steady state or "Petschek-like" and we associate this phase with magnetic energy storage. A later rapid flux transfer event is more energetic and is associated with storm events. The flux transfer event is triggered by a change in resistivity. (c) The laboratory event scales reasonably well to the duration and energy of a substorm.

Fast time structures superimposed to impulsive solar microwave bursts with slowly varying or stationary polarization degree

“…There is a non-steady interplay between the energy being built up and its release, resulting in a sort of visco-elastic relaxation oscillation. The energy storage function is shifted in phase from its release rate, and an exact match with the entry of new magnetic flux can be attained (Bratenahl and Baum, 1976). As a net result, one wouldn't expect to measure any apparent significant change in the magnetic field in correspondence to the impulsive flux transfer events.…”

“…Flare-like plasma disruptions at magnetic X-points have been obtained by Baum, Bratenahl and co-workers, in a double inverse pinch device (DIPD) which they have attributed to fast impulsive flux transfer events (IFTE) (Baum etal., 1973;Baum and Bratenahl, 1976;Bratenahl and Baum, 1976). A conduction mode instability can be set up in the DIPD, which changes abruptly the resistance at the neutral point when the reconnection current density reaches a critical value.…”

“…We might finally mention a theoretical possibility of having gravitational instabilities in long superconductive plasma tubes, which would break up into a string of explosive pieces (Chandrasekhar and Fermi, 1953). The application of this mechanism to energy conversion in solar flare was suggested (Kaufmann, 1977), and it could account for the impulses without requiring actual field annihilations.…”

Laboratory solar flare experiments

“…There is a neutral point experiment of this type known as the double inverse pinch device (DIPD) (Bratenahl and Yeates, 1970;Baum et al, 1973a, b, c;Baum and Bratenahl, 1974). The DIPD is shown schematically in Figure 1.…”

“…It is moreover clear that when the x-point current system is close to the critical state for transition to anomalous conductivity, it could easily be carried over the threshold by the compressive effects of a shock wave coming from some distant flare provided the shock hits the x-point on one of its upstream sides, the result being a sympathetic flare. It should be noted that substorm scaling was done by Baum et al (1973c).…”