A high-resolution spectroscopic system for remote measurement of plasma parameters

Abstract

Plasma diagnostics are usually performed with immersive probes that collect the cumulative electric currents created by charged particles. Idealized models are applied to the resulting I-V curves to extract plasma flow parameters. Our non-invasive technique, based on passive emission spectroscopy (PES), allows for the remote measurement of undisturbed plasma parameters via fine spectral effects. Importantly, it can be applied to each plasma species separately, including neutral components. However, extremely high spectral resolution is required to resolve shapes of the spectral lines. We describe a portable instrumentation system that delivers sub-pm resolution in visible and near-infrared regions of the spectrum. It can be used to measure various plasma parameters but most notably allows the drift velocities of ions and neutrals to be resolved with ∼100 m/s precision. We discuss details of our experimental apparatus, along with capabilities and limitations of the PES implementation.