Experimental Plasma Jet Formation in a Three-dimensional Magnetic Null Point Topology

We demonstrate the formation of an approximately 15 cm plasma jet resulting from the operation of a coaxial plasma gun (CPG) within a strong (0.7 T) three-dimensional magnetic null point field (3D null point). Circuit control is established to operate a CPG with a gas puff inlet and a 3D null point conducting coil assembly, all within a low pressure environment (under 1 Torr). Two separate multi-kilovolt capacitor banks are configured to discharge simultaneously so that the CPG plasma interacts with the spine axis of the strong 3D null point. High-speed camera imaging elucidates the differences between conventional CPG operation and the CPG operating within the strong magnetic field. Deflagration of the gas puff CPG precedes the snowplow mode of plasma sheath formation as confirmed with Rogowski coil diagnostics. During simultaneous operation, the peak CPG snowplow mode occurs during magnetic field ramp-up and approximately 120 µs before the peak magnetic field strength, which is accompanied by an unambiguous plasma jet forming along the spine axis of the 3D null point. This demonstrated snowplow plasma sheath injection into a 3D null point field represents the first known experimental test of plasma and magnetic field dynamics known to lead to 3D torsional magnetic reconnection.