The time-integrated spectroscopic measurements of argon plasma are carried out to characterize the transient plasma stream produced in a coaxial pulsed plasma accelerator. Transient plasmas produced in these types of devices have a temporal change in density and temperature. The temporal evolution of the plasma stream and its characteristic variation are studied from a time of 50–300 μs in steps of 50 μs. Analysis of different spectral lines shows the existence of some metastable states of Ar+ having a long lifetime. The evolution of different Ar+ transitions to metastable and non-metastable lower levels is observed for different time frames. From the Stark broadening and Boltzmann plot method assuming the partial local thermodynamic equilibrium model, the plasma densities and excitation temperatures are estimated. The temporal evolution study shows a decrease in plasma densities from 1.96 × 1021 m−3 at 50 μs to 1.23 × 1020 m−3 at 300 μs after the initiation of plasma formation. A reduction in excitation temperature is observed from 0.86 to 0.77 eV. Based on the density profile, the estimated energy density of the plasma stream shows a time-dependent decreasing trend from 0.06 to 0.004 MJ/m2 during the observed period. The results may be useful for optimization of the plasma stream in pulsed plasma accelerators concerning its different parameters.

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An experimental study on the role of an external longitudinal magnetic field on the characteristics changes of pulsed plasma stream, produced in argon medium, is carried out at different time spans of its evolution. The spectroscopic observations are time integrated and are carried out at different times of plasma formation for pulsed discharge. This study gives insights into the recombination and diffusion phase of the plasma species in the presence of the magnetic field. The transition of plasma species from a dominant recombination phase to a diffusional phase is well revealed by the density profile during the time evolution. Moreover, the decrease in electron temperature and the increase in electron excitation temperature explain the energy transfer to electrons due to metastable quenching, and the system gradually approaches equilibrium. The magnetic field also affects the transitions of the ionized argon population between different energy levels. It is found that faster decay occurs for transitions of different plasma species to non-metastable states, while the populations of metastable states exist for a longer time. In addition, the time-resolved morphology changes of the plasma stream are also observed by high speed imaging, which shows the flow structure of the plasma stream at different time frames. The imaging of the plasma stream evolution shows the initial ejection of the plasma sheet from the electrode assembly, its detachment, the steady flow, and gradually its nature of dying out.

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