Solar Vacuum Ultraviolet Testing Activities at the Space Plasma, Power and Propulsion Laboratory

The Sun emits light in the 100 - 200 nm wavelength range, known as the vacuum ultraviolet (VUV). Furthermore, the brightest Solar emission line, Lyman-α Ly-α, occurs at 121.6 nm. Whilst the Solar VUV is absorbed by the Earth’s atmosphere and thus not observed on the Earth’s surface, it plays a significant role in physical processes in our Solar System. Processes include the formation of ozone and photoionisation of nitric oxide to form Earth’s ionospheric D-layer, degradation of polymers, coatings and optical elements on spacecraft, and charging of dust on the surface of the Moon leading to malfunction of various mechanical, thermal, optical and electrical systems. The development of space systems requires testing in high-fidelity simulations of the space environment. The range of currently available VUV sources can only illuminate small areas, have a mismatched spectral distribution or emit low fluxes, making them unsuitable for conducting these tests. At the Space Plasma, Power and Propulsion Laboratory (SP3), we have developed a VUV source based on a mixed-gas, radiofrequency plasma that mimics the Solar spectrum in the 100-170 nm wavelength range. By variation of the gas mixture and pressure, the source can also output quasi-monochromatic Ly-α radiation. In this work, we describe the design and characterisation of the source and outline several potential testing use-cases.