Three-dimensional Evolution and Formation of Multiple Current-filaments in a Laboratory Arched Magnetized Plasma*

The study and understanding of fundamental processes taking place in arched magnetized plasmas is relevant to space and magnetic fusion plasmas. We present new results on measurements conducted on laboratory arched magnetized plasmas produced using a hot-cathode lanthanum hexaboride (LaB₆) source. The arched plasma evolves in an ambient magnetic field (0-80 Gauss). Typical plasma parameters are: β≈10³, Lundquist number ≈10²-10⁵, plasma radius/ion gyroradius ≈20, B≈1000 Gauss at footpoints, and 0.5 Hz repetition rate. Evolution of the arched magnetized plasma has been recorded under different ambient magnetic fields. Experimental results demonstrate that the application of a stronger ambient magnetic field results in outward or inward motion of the leading edge of the arched plasma (depending on the direction of the net JxB force). In addition, this motion is accompanied by generation of multiple-current filaments that form a complex three-dimensional structure. We present results on experimental measurements of plasma density, electron temperature, and magnetic-field using dual-tip Langmuir probes, a three-axis magnetic-loop probe, and a recently developed 3D probe drive system.