Experimental evaluation of common spacecraft data analysis techniques for reconnection region analysis in a laboratory plasma

A laboratory plasma is utilized to assess the effectiveness of several prominent spacecraft data analysis techniques. These include minimum variance analysis on the magnetic field (MVAB) and various boundary-crossing time analyses (BCTA) such as the constant velocity approach (CVA), constant thickness approach (CTA), and minimum thickness variance (MTV). Magnetic field data from measurement points that resemble the formation of multispacecraft flying though a reconnecting current sheet is used to check MVAB and BCTA to deduce a proper normal vector. Results from each method are compared to the values measured by 2-D magnetic probe arrays. We examine discharges with a two-dimensional (2-D) X-line structure as well as cases in which a flux rope forms within the layer. All discharges are in a two-fluid regime in which electrons are magnetized but ions are not. We conclude that CVA with four sample measurement points forming a tetrahedron generates a reasonable unit normal vector n, relative velocity along the normal vector V_n, and current sheet thickness δ_CS for all of the tested cases. Unlike CVA, both CTA and MTV sometimes generate V_n and δ_CS that are different from the measured values, which indicates that CTA and MTV are sensitive to changes in the current sheet thickness. CTA is, however, successful at estimating n. MVAB, on the other hand, often fails to predict a proper normal direction. This is because the reconnecting neutral sheet fundamentally contains 2-D or 3-D structures. MVAB, however, does determine the direction along the reconnecting magnetic field that is close to the real magnetic geometry. Based on these observations, we suggest a hybrid procedure for determining a local coordinate system for data from four spacecraft passing through a reconnecting current sheet.