Measurements of Plasma Jets and Collimated Flux Tubes that are the Precursors of Spheromak Self-organization

A magnetized planar coaxial plasma gun is used to study the physics of spheromak formation. Eight magnetic flux tubes spanning from the cathode to the anode electrode are first filled with plasma by a rapid MHD pumping mechanism which ingests plasma from nozzles at the wall. The ingested plasma convects toroidal flux and the pile-up of this flux in the flux tube causes the flux tube to become collimated. The eight collimated flux tubes first have the shape of spider legs, but then merge to form a central column jet. This jet lengthens, continuing to ingest plasma from the wall sources, and becomes kink unstable. At a later stage the root of the jet can break off from the electrode and this detachment has been identified as being associated with a sausage instability. The sausage instability takes place during the nonlinear stage of the kinking. The above statements are based on experimental observations and have been reconciled with MHD models.