Exploring MHD-driven plasmas created using different amounts of magnetic helicity injection and relevance to MHD jets and spheromaks*

MHD-driven plasmas generated by a disk electrode surrounded by a coplanar annulus electrode form various topological configurations such as a collimated straight jet or a spheromak depending on the amount of helicity injection. Morphology is tracked using the combination of visible light movies and 3-D volumetric magnetic probe measurements. In the regime where the plasma detaches from the electrodes, a magnetic island is observed in the poloidal direction indicating formation of a closed surface flux and thus formation of a spheromak. This detachment is accompanied by X-ray bursts and magnetic oscillations in the range of whistler frequencies.  Since spheromak formation requires magnetic reconnection, the observed X-rays and high-frequency magnetic oscillations are presumed to be evidence of magnetic reconnection by which the plasma dissipates energy and evolves into a spheromak.