Bremsstrahlung radiation from toroidal plasmas generated through hydrodynamic shear

Abstract

In this work, we investigate the anomalous appearance of bright visible light from a toroidal argon plasma generated through extreme hydrodynamic shear. In ambients of nitrogen or helium, the spectral content is easily correlated to the plasma’s color. In an argon ambient however, infrared spectral lines dominate the spectrum, while the plasma appears light blue, nearly white, to the naked eye. We determine that this luminescence is a visible broadband continuum emitted by electrons scattering off neutral argon atoms, a form of radiation called bremsstrahlung radiation (ϵea). Using multispectral imaging, we calculate the temperature, T_e, of bremsstrahlung-producing electrons spatially throughout the plasma, up to the ionization energy of argon atoms 15.76 eV. We further provide a method of calculating electron density, n_e, from the same data. We find that in both the T_e and n_e fields, two distinct phases appear; a small inner ring of high T_e, low n_e, and an outer diffusive region with low T_e, high n_e. The boundary between these disparate phases is extremely small, less than 10 µm, indicating an element of self-confinement intrinsic to this plasma configuration.

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