Current Systems Generated by Colliding Laser-Produced Plasmas

There are many situations, either in space (e.g. CMEs, supernovae), or man-made, in which a dense plasma expands into a magnetized background plasma capable of supporting Alfv\'{e}n waves. The generation of shear Alfv\'{e}n waves by an expanding laser-produced plasma (lpp) has been observed previously at the LArge Plasma Device at UCLA [1]. In a recent experiment at LAPD, the collision of two dense ($\delta $n/n$_{0} \quad >>$ 1, where n$_{0} \quad \sim $ 1-4 x 10$^{12}$/cm$^{3})$ lpps within an ambient, highly magnetized ($R_{ci} \quad \sim $ 4mm $<< \quad \Delta \quad \sim $ 1m, where $\Delta $ is the machine diameter) is studied. A 150MW laser is pulsed with the background plasma at 1Hz, in a reproducible experiment to obtain a large volumetric dataset. We have directly observed a system of complex, fully 3-dimensional time-dependent current systems associated with the shear Alfv\'{e}n waves generated by the two lpps. The magnetic helicity associated with these current systems will be presented and compared to their topology, along with a process which strongly resembles magnetic reconnection at a point where the two current channels pull apart. Data will be presented as a 3-D movie. \newline \newline [1] M. Van Zeeland \textit{et al}, Phys. Rev. Lett., \textbf{87}(10):100501-1-100501-4, 2001.