Inductively Coupled Radio-frequency Plasmas as Solar Vacuum Ultraviolet Simulators

The solar vacuum ultraviolet (VUV) is relevant to a variety of astrophysical phenomena. Radio-frequency (RF) plasmas of H₂ and H₂/inert gas mixtures are convenient sources of VUV for laboratory simulations. In previous work, we made extensive measurements of the emission spectra for the full range of H₂ plasmas mixed with He, Ne, and Ar. In this work, we examine these data in the context of simulating the solar VUV. It was found that a gas mixture of 35% H₂ : 65% Ar at 20 mTorr best mimics the solar spectrum in the range 110-160 nm. Spatially resolved optical measurements were used to estimate the spatial distribution of the plasma emissivity, and compared with photodiode measurements to estimate the total power emitted from the plasma in the VUV. At 400 W RF input power, approximately 32% (126 W) was emitted in the VUV spectral range, attenuated to 84.8 W by the MgF₂ window. Fluxes in the range 10-40 mW cm⁻² were detected, varying with distance from the source aperture, enabling accelerated testing in a simulated space environment with up to 4000× equivalent solar VUV fluxes.

Unified Astronomy Thesaurus concepts: Laboratory astrophysics (2004); Plasma physics (2089); Solar ultraviolet emission (1533)