Uniform, Filamentary, and Striped Patterns in Helium Dielectric Barrier Discharge Cryoplasmas

Dielectric barrier discharge cryoplasmas were generated in helium at temperatures between 192 K and 7.6 K at pressures between 1.2 × 10⁵ and 5.2 × 10³ Pa. Different discharge structures were observed, such as uniform glow, filamentary, and striped patterns, whose formation depends on the neutral gas temperature, applied voltage, and frequency. At higher temperatures, in addition to He, optical emission spectra include bands due to impurities such as N₂, while at temperatures below 20 K, only peaks due to He and He₂ are observed.