Thomson scattering diagnostics of electron density and electron temperature in cascade arc argon-helium and argon-neon mixture plasmas

Abstract The cascaded arc plasma source is a significant plasma-generating device capable of producing high-density, steady-state plasma in a low-pressure environment. The two most crucial physical parameters of the plasma are the electron density ( n e ) and electron temperature ( T e ). The laser Thomson scattering (LTS) technique provides an accurate method for measuring both n e and T e . In this study, we conducted diagnostic measurements of n e and T e for cascaded arc argon-helium (Ar-He) and argon-neon (Ar-Ne) mixture plasmas utilizing LTS technology. Furthermore, we explored the local thermodynamic equilibrium (LTE) state of the plasma by comparing the electron excitation temperature ( T exc ) obtained through optical emission spectroscopy (OES) with T e measured via LTS. Our results indicate that varying the dopant ratios of the gas mixtures, alongside the experimental currents and background pressures, influences both n e and T e . Specifically, these parameters are inversely proportional to the dopant ratio, while they are directly proportional to the background pressure and discharge current. Notably, at the same dopant ratios, n e and T e are slightly elevated in the presence of Ne dopants compared to those with He dopants. Additionally, the observed differences between T exc and T e suggest that the cascaded arc mixture plasma deviates significantly from the LTE state. This deviation is directly proportional to the dopant ratio and inversely proportional to the discharge current. The findings contribute to a deeper understanding of multicomponent plasmas and potentially enhance the applications of cascaded arc mixture plasmas.