Time-Variant Microwave Absorption by Dielectric Barrier Discharge Plasma in Atmospheric Pressure Helium

A numerical investigation is performed to analyze the transient microwave absorption characteristics of parallel-plate helium dielectric barrier discharge (DBD). Because the plasma has rapid temporal and spatial variation, a time-variant plasma fluid model is used to track the change of plasma variables over time. When an ac voltage of 4.7 kV and an ac frequency of 10 kHz are supplied to the DBD, the plasma operates as cold-collisional plasma under atmospheric pressure. The calculation of the plasma fluid model shows that predominant peaks in electron density and temperature appear twice in a period of $105.26~\mu \text{s}$ , which suggests uniform glow discharge. These variables can be converted to plasma frequency and collision frequency, respectively. Then, the results are reflected in a complex wavenumber of the Maxwell equation to calculate the amount of wave absorption. When a microwave of 10 GHz is launched toward the DBD, the absorption behaves as a function of plasma variables with the maximum at every discharge with an interval of $52.63~\mu \text{s}$ . The time-varying absorption shows good agreement with the existing experimental measurement. The absorption is also studied as a change of gas discharge parameter. The increase in applied voltage bolsters the amount of absorption up to 2 times.