Estimation of Atmospheric Pressure Plasma Electron Density for the Validation of a Heterodyne Dispersion Interferometer

Laser interferometers enable direct and nonintrusive measurements of fundamental plasma properties, such as line-averaged electron density (n_e). However, in the case of Atmospheric Pressure Plasmas (APPs), the small, n_e-induced phase shift signal measured by the interferometer can often be masked by phase shifts due to variations in refractive index caused by neutral gas density changes. Mitigation of these unwanted phase shifts can be achieved with an instrument known as the Heterodyne Dispersion Interferometer (HDI). A CO₂ laser HDI has been developed and will be used to measure a DC-pulsed APP. Since HDIs have only rarely been deployed to measure APPs, this work will discuss the production of analytic estimates of n_e using transport parameters output by the BOLSIG+ electron Boltzmann equation solver. To evaluate the applicability of BOLSIG+ to the DC-pulsed APP, these estimates will be compared to the n_e of a similar DC-pulsed plasma measured in previous works. These estimates will be compared to HDI measurements, with discrepancies analyzed and discussed.