Study of transient plasma stream using Time-Integrated Spectroscopic Technique

Abstract

Time integrated spectroscopic measurements are carried out to characterize transient plasma stream produced in a coaxial pulsed plasma accelerator. This method allows the estimation of different plasma parameters and its evolution with time. It also provides information on the existence of different excited states from the spectral emissions of plasma. Using Argon as the discharge medium, the electron density estimated from Stark broadened line profiles gives a peak value $\sim 5 \times 10^{21} m^{-3}$ at a discharge voltage of 15 kV and the flow velocity of the plasma stream is measured to be $\sim (22 + 5)$ Km using Doppler shift method. Assuming p-LTE model, the electron excitation temperature is found to be $\sim 0.88$ eV using Boltzmann plot method. A temporal evolution of the plasma stream and its characteristic variation is studied from a time of $50 \mu s-300 \mu s$ in steps of $50 \mu s$ by adjusting delay time in the triggering. Analysis of different spectral lines shows the existence of some metastable states of Ar II having a long lifetime. The evolution of different Ar II transitions to metastable and non-metastable lower levels is observed for different time frame. The temporal evolution study shows a decrease in electron density from $1.96 \times 10^{21} m^{-3}$ to $1.23 \times 10^{20} m^{-3}$ at $300 \mu s$ after the initiation of plasma formation. A decrease in excitation temperature from 0.86 eV to 0.72 eV is observed till $250 \mu s$ and then again rises to 0.77 eV at $300 \mu s$