Optical and electrical analysis of a temperature-dependent mode transition of a helium cryoplasma

A novel plasma source that can be generated at a cryogenic temperature, the so-called cryoplasma, was established under atmospheric pressure. Our cryoplasma system can easily control the processing temperature from room temperature down to 78 K using liquid nitrogen. We employed a dielectric barrier discharge reactor, which was connected to an ac power supply, and we flowed helium as the discharging gas. We found that plasma phenomena such as the discharge pattern and color showed temperature-dependent behavior as the gas temperature decreased. Furthermore, this result was closely related to changes in not only the emission spectra measured by optical emission spectroscopy but also the waveforms of the discharge currents and voltages. We concluded that the change in gas temperature induced a transition in the discharge modes.