Numerical investigation of the directional control of electron density and gas temperature in atmospheric pressure dielectric barrier discharge by using low- and high-frequency coupling modulation

Abstract

Dielectric barrier discharges (DBDs) are commonly used as efficient sources of large volume diffuse plasmas with moderate temperature and plenty of reactive particles, but the synergistic linkage of some key plasma parameters in single frequency driven systems sometimes limits their application fields and accessible operating ranges. The discrete control of certain key plasma parameters by multi-frequency, i.e., dual frequency (DF), voltage waveform excitations is of increasing requirement and importance for both application-focused and fundamental studies on DBD plasma. In this paper, a significant nonlinear coupling modulation of the discharge evolution process and characteristics caused by the HF oscillation of the high-frequency component in the DF DBD system is observed and investigated, which provides a simple and efficient approach to realize the independent control of the target key plasma parameters such as gas temperature and electron density. Based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of the tiny high frequency component on the properties modulation of atmospheric DF DBD are reported. The driving voltage waveform is characterized by a 50 kHz fundamental sinusoidal low-frequency signal superimposing a small amount of 2 MHz high-frequency signal [HF component changing from 0 to 100 V with a low-frequency (LF) component fixed at 1 kV as a constant], and the effects of the high-frequency voltage amplitude and phase shift on the discharge characteristics, sheath dynamics, impact ionization of electrons, and key plasma parameters are investigated. Particularly, the effects of phase modulation on the discharge evolution and characteristics for DF DBDs are discussed and revealed. The results have demonstrated that a slight and proper parameter variation of the high-frequency oscillation can provide a high electron seed density, and trap electrons within the sheath, thus achieving required plasma parameters. The sheath dynamics can be effectively modulated by tuning the phase shift, which enables a possible alternative approach to optimize the independent control of the key plasma parameters under atmospheric pressure.