# Two-Colour Interferometry and Thomson Scattering Measurements of a Plasma Gun

## TL;DR

This paper reports on experimental measurements of a pulsed plasma gun using two-colour interferometry and Thomson scattering, providing detailed electron density and temperature data, and discussing spectral broadening and asymmetries.

## Contribution

The study combines two-colour interferometry and Thomson scattering to simultaneously measure electron density and temperature in a plasma gun, revealing discrepancies and spectral asymmetries.

## Key findings

- Electron density of approximately 2.7×10^{17} cm^{-3} measured at 5 mm from nozzle.
- Electron temperature around 10 eV from non-collective scattering and 30 eV from collective scattering.
- Observed spectral asymmetries suggest kinetic effects influencing electron distribution.

## Abstract

We present experimental measurements of a pulsed plasma gun, using two-colour imaging laser interferometry and spatially resolved Thomson scattering. Interferometry measurements give an electron density $n_e\approx2.7\times10^{17}$ cm$^{-3}$ at the centre of the plasma plume, at 5 mm from the plasma gun nozzle. The Thomson scattered light is collected from two probing angles allowed us to simultaneously measure the collective and non-collective spectrum of the electron feature from the same spatial locations. The inferred electron densities from the location of the electron plasma waves is in agreement with interferometry. The electron temperatures inferred from the two spectra are not consistent, with $T_e\approx 10$ eV for non-collective scattering and $T_e\approx 30$ eV for collective scattering. We discuss various broadening mechanisms such as finite aperture effects, density gradients within the collective volume and collisional broadening to account for some of this discrepancy. We also note the significant red/blue asymmetry of the electron plasma waves in the collective scattering spectra, which could relate to kinetic effects distorting the distribution function of the electrons.