Ubiquitous Plasma Motions in Magnetized Plasma Arcades with Different Experimental Configurations

Magnetized plasma arcades and flux ropes appear in space and astrophysical contexts and have been the subject of recent laboratory, observational, and computational studies. We generate arcade-shaped plasmas in the lab using two parallel copper electrodes and a magnetic coil surrounding the electrodes. We compare and contrast behavior with short (5 cm) and long (20 cm) cathodes and a variety of hydrogen gas fueling methods with the aim of more reproducible plasmas amenable to combining measurements across multiple shots. ICCD cameras, photodiode arrays, and fast current and voltage measurements are used to characterize the discharges. We observe that all configurations share the common features of (i) shifts in discharge location along the electrodes within a shot and (ii) repetitive, fast-moving current filaments that propagate through the arcade. Both types of plasma motion persist even when fueling through a single hole in the cathode. The most reproducible operations are obtained with high vacuum magnetic fields, localized fueling through the cathode, and diffuse fueling near the anode. However, even in this case, significant shot-to-shot variations remain.