Effects of Frequency on the Electrical Characteristic of Pulse Discharges in Atmospheric-Pressure Pure Helium

The effects of the frequency on the electrical characteristics in a dielectric barrier discharge in pure helium excited by repetitive voltage pulses with the frequencyffrom 5 to 500 kHz are systematically investigated by means of a 1-D fluid model under different operating conditions, including gap widthdg, secondary electron emission coefficient γ, dielectric thicknessds, and dielectric constant εr. The important characteristic quantities of describing the pulse discharge, i.e., discharge current densityJg, averaged electron densityNave, averaged dissipated power densityPave, and the axial distributions of both electron densityNeand electron temperatureTe, are calculated and analyzed in detail. This paper gives the following significant results.Naveincreases with increasingfandPaveis almost proportional tof. Especially, there is a characteristic frequency of ~ 50 kHz, namely, whenfis lower than ~ 50 kHz,Jm1 (peak value ofJgin the first discharge) decreases evidently with increasingf, and then changes very slightly forfs larger than ~ 50 kHz. In addition, with the increase off,Jm2 (peak value ofJgin the second discharge) increases very slightly for smalldsand the reverse is true for largeds. The frequency dependence ofJm2 for different εrsis similar to that by changingds. For a fixed frequency, the change ofJm1 with γ is very small, which differs from that at low frequencies. In addition,Jm1 andJm2 decrease with increasingdsand increase with increasing εr, but there are almost constant ΔJm1 and ΔJm2 for high frequencies. When the frequency is larger than ~ 50 kHz, there will be the second peak ofNeoutside the cathode sheath in the first discharge, and both largedsand small εrcan result in the formation of the evident peak ofNenearby the momentary anode. It should be noted that the analysis in this paper pertains only to the incompressible motion of the plasma.