Further Insight into the Nature of Atmospheric Water Plasmoids

There is a great deal of interest in pulsed atmospheric plasmas for applications in plasma chemistry, medicine and others. Here we study a plasma formed by a pulsed discharge (250 kW -- 1,350 kW) in water. In previous studies, a high-voltage capacitor bank was discharged between a cathode protruding from a container of weakly conducting electrolyte (Stelmashuk, Vitaliy {\&} Hoffer, P., IEEE, Trans. Plasma Sci, 2017) and a submerged ring anode. A plasmoid was produced and its light emission was photographed using a fast camera. This work extends these studies with the imposition of a magnetic field (100 G \textless B \textless 2 kG) parallel to the cathode. The long-lived plasmoid (t \textgreater 1 sec) was photographed with a fast framing camera (30,000 frames/sec). The highly collisional plasma was observed to rapidly rotate when the field was present. B-dot probes with onboard electronics and no connection to ground measured coherent low frequency fluctuations (f $=$ 50 Hz), which became chaotic at larger input powers. The photography revealed ``firefly'' streamers that drift away from the mushroom cloud above the spinning vortex. Aside from movies we present data from magnetic probe arrays, plasma density measurements and spectra.