Determination of the Electron Density in an Argon Plasma Jet Using Absolute Measurements of Continuum Radiation

Abstract

We present a method to determine the electron density, ne, of an argon plasma jet using the continuum radiation. The radiation measurements are calibrated with a standard tungsten filament lamp. Due to the filamentary nature of these plasmas, it is not possible to use the spectral radiance W m−2 nm−1 sr−1 as the radiometric quantity. Instead we work with the spectral irradiance W m−2 nm−1. As the ionization degree is low, the continuum radiation is predominantly generated by interactions of electron with atoms; the influence of electron–ion interactions can be neglected. The method provides ne values of about 7 × 1019 m−3 in the active zone for an argon plasma created by a sinusoidal peak to peak voltage of 10 kV. Comparison with the ne values determined via the current density shows a fair agreement; this comparison can only be done for the region between the electrodes. In the afterglow region, where the current‐density method cannot be applied, we can still use the continuum radiation to determine ne. It is observed that ne decreases in the afterglow direction down to 2 × 1017 m−3.

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