The distribution pattern of the electron density and the electron temperature in a weakly compressible argon plasma jet measured by a Langmuir triple probe

High-speed plasma plays an important role in diverse areas. Plasma flow with a sufficiently high speed to arouse compression is usually not in thermal equilibrium, and the plasma characteristics are closely coupled with the flow field. The relation between the flow and the plasma parameters, especially the distributions of electron density, i.e. n (e), and the electron temperature, i.e. T (e), are of ultimate importance; however, this is not yet completely understood. In this work, a weakly compressible plasma jet produced by an arc torch is diagnosed using a Langmuir triple probe. The two-dimensional distributions of n (e) and T (e) are obtained consisting of 80 spatial points under arc currents of 70-100 A. The spatial patterns of the distributions demonstrate alternative expansion-compression wave structures. As the arc power increases, the wave structures remain almost unchanged, while n (e) increases monotonically. Moreover, in some regions T (e) decreases with the arc power, which has seldom been reported in the literature. In addition, the peaks of the radial distributions of T (e) always deviate from the central axis. These results are compared with previous works of strongly compressible plasma flows. The phenomena are then analyzed and explained from the perspective of fluid wave-plasma interactions and the actions of the ambipolar field in the electrons.