Detection of shock structure around Mach disk in axisymmetric plasma jet

Abstract

Plasma jets have been used widely in various fields such as materials and aerospace engineering. The understanding of the shock structure is important to control a supersonic jet using a magnetic field. An experiment of axisymmetric argon plasma jet under strong magnetic field was carried out to detect the shock structure around the Mach disk precisely. A magnetic field was applied to the jet using a pair of identical superconducting coils. The jet images in a vacuum chamber were taken by a digital single-lens reflex camera with high spatial and color resolution through a viewing window. The distribution of light intensity from photographic data was converted to the radial intensity, relevant to plasma density, using Abel-inversion. The radial shock structure, that is not apparent on the ordinary photos, can be detected from the converted distributions. The software for the analysis was developed to detect the shock structure in the plasma jet. The method of shock detection was also detailed. The hidden shock characteristics such as triple point were found using the radial intensity obtained from the data with high color resolution. The shock lines upstream of the Mach disk under the magnetic field were indicated in detail. The reflected shock location could be determined. The intensity distribution downstream of the Mach disk was significantly changed by applying the magnetic field. The interaction between plasma density and magnetic field clearly occurs at higher density region downstream of the Mach disk.