Plasma formation and ablation dynamics of stainless steel cylindrical liner

Using laser shadowgraphy and interferometry on a Qin-1 facility, the initial plasma formation and dynamics of an exploding stainless steel liner were investigated. To obtain the absolute electron density distribution inside the liner, we established continuous wave laser interferometry using a streak camera to measure the shift in the fringes over time. Plasma is generated at the interior wall and flows toward the center with a velocity of ∼100 km/s, thus forming a column with higher density by accumulation. Simultaneously, a high-density plasma layer is formed near the interior surface and this layer flows toward the center at approximately 10 km/s. In addition, magnetohydrodynamics (MHD) instabilities were observed at the exterior surface using side-on laser shadow images at a much later time (∼400 ns). The growth in the amplitude and the wavelength of the perturbations were then analyzed. An MHD simulation of this process was then established to demonstrate that the high-density plasma layer carries part of the current and that it flows within the 10 km/s range after comparison with the experimental results. Finally, we measured the voltage and derived the change in the inductance. The results prove that part of the current flows through the center plasma column, which then influences the subsequent plasma flow.