Measurement of electron density and electron temperature of a cascaded arc plasma using laser Thomson scattering compared to an optical emission spectroscopic approach

As advanced linear plasma sources,cascaded arc plasma devices have been used to generate steady plasma with high electron density,high particle flux and low electron temperature.To measure electron density and electron temperature of the plasma device accurately,a laser Thomson scattering (LTS) system,which is generally recognized as the most precise plasma diagnostic method,has been established in our lab in Dalian University of Technology.The electron density has been measured successfully in the region of 4.5 × 1019 m-3 to 7.1 × 1020m-3 and electron temperature in the region of 0.18 eV to 0.58 eV.For comparison,an optical emission spectroscopy (OES) system was established as well.The results showed that the electron excitation temperature (configuration temperature) measured by OES is significantly higher than the electron temperature (kinetic electron temperature) measured by LTS by up to 40％ in the given discharge conditions.The results indicate that the cascaded arc plasma is recombining plasma and it is not in local thermodynamic equilibrium (LTE).This leads to significant error using OES when characterizing the electron temperature in a non-LTE plasma.