Optical Analysis of Nanosecond-Lifetime Plasma Parameters

We present observations and modeling of argon gas at pressures of a few Torr that have been excited with high-voltage pulses (hundreds of volts) on the order of nanoseconds in duration. These tests are motivated by an effort to determine the feasibility of utilizing pulsed argon plasma as a conducting media in a novel antenna configuration. A vacuum chamber is constructed with plate electrodes inserted. An optical observation system is constructed to observe the temporal response. The rise time and fall time of the plasma’s optical emissions, taken as a proxy of the electron density, are measured as a function of pulse voltage and pressure using the captured optical light curve. In addition, spectroscopy measurements are made on a longer time scale. The maximum electron density of the plasma is then inferred through the use of PrismSPECT, a commercially available collisional radiative model, via the line ratio method. Measured pulsed plasmas reached their maximum ionization in as low as 5 ns and recombine in as low as 140 ns. Spectral measurements show that a 1-Torr plasma ionized with 5-ns long pulses had a maximum electron density of $5.2\times10\,\,^{\mathrm{ 20}}$ /m3 and maximum electron temperature of 1.28 eV.