Time-Resolved Measurements of Plasma Parameters for Nanosecond-Pulsed Argon Plasmas

Abstract

This article aims to understand the physics of pulsed plasmas by investigating the ionization and recombination of pulsed plasmas on the nanosecond timescale and how operating conditions affect the time-resolved electron temperature and electron density of a pulsed plasma. A nanosecond-pulsed argon plasma discharge was generated at various pulse frequencies, widths, and pressures. The argon emission lines were analyzed with a time-synchronized, intensified charge-coupled device (ICCD) spectrometer assembly that gated at 4 ns, and relative intensities of strong argon neutral and ion lines were used in line-ratio calculations. These experimentally determined ratios were compared to theoretical ratios generated from PrismSPECT, a collisional-radiative spectral analysis software, to obtain time-resolved electron temperature ( $\sim 1$ eV) and electron density ( $10^{14}-10^{15}$ cm $^{-3}$ ) over the various operating conditions as well as to discover trends of these plasma parameters over the lifetime of the pulsed plasma. Increasing pulse repetition frequency of the plasma increased the value of maximum $T_{e}$ , shortened the $T_{e}$ rise and decay times, and increased the excited argon neutral population. While $n_{e}$ was relatively independent of pulse frequency, higher pulse frequencies resulted in a faster $n_{e}$ decay. Maximum $T_{e}$ and $n_{e}$ were weakly dependent on applied discharge voltage, but both parameters decayed sooner in time with increasing voltage. Lastly, $T_{e}$ was inversely proportional to pressure, but $n_{e}$ was approximately linear. All three pressures had similar but time-shifted temporal profiles for $n_{e}$ . Plasmas in all operating conditions had ionization and recombination times in the tens of nanoseconds.