D Reconnection and Flow Dynamics in the Ssx Experiment

Several new experimental results are reported from plasma merging studies at the Swarthmore Spheromak Experiment (SSX) with relevance to collisionless three-dimensional magnetic reconnection in laboratory and space plasmas. First, recent high-resolution velocity measurements of impurity ions using ion Doppler spectroscopy (IDS) show bi-directional outflow jets at 40 km/s (nearly the Alfven speed). The SSX IDS instrument measures with 1 μs or better time resolution the width and Doppler shift of the C_III impurity (H plasma) 229.7 nm line to determine the temperature and line-averaged flow velocity during spheromak merging events. High flow speeds are corroborated using an in situ Mach probe. Second, ion heating to nearly 10⁶K is observed after reconnection events in a low-density kinetic regime. Transient electron heating is inferred from bursts on a 4-channel soft x-ray array as well as vacuum ultraviolet spectroscopy. Third, the out-of-plane magnetic field and the in-plane Lorentz force in a reconnection volume both show a quadrupolar structure at the ion inertial scale (c/ω_pi). Time resolved vector magnetic field measurements on a 3D lattice B(r, t)) enables this measurement. Earlier work at SSX has shown that formation of three-dimensional structure at the ion inertial scale is temporally and spatially correlated with the observation of superthermal, super-Alfvenic ions accelerated along the X-line normal to the local 2D plane of reconnection. Each of these measurements will be related to and compared with similar observations in a solar or space context. Keywords: spheromak, flow, heating.