Investigation of current sheet disruptions using laser-produced diamagnetic bubbles

Rapid temporal changes in the magnetic field topology of current-carrying plasmas can enhance or disrupt these currents and trigger magnetic reconnection. A clear natural example of this can be found in the earth's magnetotail during a magnetic substorm. In this laboratory study, preliminary results are presented of an effectively steady-state current sheet which is disrupted by the production of an impulsive diamagnetic bubble. The process is impulsive in that it occurs on a timescale less than the ion cyclotron period. The experiments are performed on UCLA's Large Plasma Device (LAPD). This is a linear device with $L$=17m, $d$=60cm, 300G$< B_{0}<$2kG, n$_{e}$=$2\times10^{12}$cm$^{-3}$, $T_{e}$=6eV,$T_{i}\approx$1eV, and He, H, or Ar). The diamagnetic cavity is produced by a pulsed (8ns, 1J) Nd:YAG laser-solid target ablation. The current sheet is produced using a $CeB_{6}$ cathode, embedded within the main plasma column,($h$=10cm, $w$=1cm). In the current sheet, the plasma has higher density, $n\approx 4\times 10^{12}$cm$^{-3}$, yielding scaled cross-field dimensions of $h=0.9c/\omega_{pi}$ and $w=3.8c/\omega_{pe}$ for a H plasma. Results will be presented which include fast camera imaging, magnetic field probe data, and the resulting time varying currents during the event.