Kelvin-Helmholtz Instability in Magnetized Plasma.

摘要

Sheared flows, found in many systems in the universe, are generally Kelvin-Helmholtz unstable. If the medium is ionized, the presence of a magnetic field can influence the evolution of this instability; depending on its strength and orientation, the field has either a stabilizing or destabilizing effect. We performed several experiments to gain insight into the underlying physics. In one type of experiment, with a laser produced plasma expanding in an external magnetic field, we observed the Kelvin-Helmholtz instability growing at the plasma-field boundary, where a velocity gradient perpendicular to the plasma velocity forms. The magnetized Kelvin-Helmholtz instability was further investigated using intrinsically magnetized pulsed power-generated plasma flows. The flows were produced by using quasi-planar arrays of wires inclined such that their connections were closer at the cathode than at the anode. A foil placed on the axis of the system introduced a transverse gradient of the axial velocity of the flow. In both experiments, the time evolution and the morphology of the Kelvin-Helmholtz vortices were investigated with laser diagnostics. The laser produced plasma was further investigated in the absence of an externally applied magnetic field. Magnetic probes were placed at several distances from the target and measured three orthogonal projections of a self-generated magnetic field found in the expanding plasma.