Driving frequency effects on the characteristics of atmospheric pressure capacitive helium discharge

Atmospheric pressure helium discharge characteristics were investigated for varying driving radio frequencies in the range between 1.86 and 27.1 MHz. As the driving frequency is raised, both gas breakdown and α-γ transition voltages decrease due to the reduction in the electron drift loss. In addition, different discharge features such as normal, abnormal, α, and γ modes show certain dependences on the frequency. Using a simple circuit model, the changes in sheath thickness from 2.35 to 0.11 mm, electron density from 0.26 to 15.6×10¹¹ cm^-3 was obtained by raising the frequency from 1.86 to 27.1 MHz.