Comparison of Atmospheric-Pressure He and Ar Plasma Jets Driven by Microsecond Pulses

In order to compare the characteristics of plasma jets in He and Ar, the plasma jets are driven by a home-made microsecond pulse power, which provides 0-30-kV output voltage with a rise time of 0.5 μs and full-width at half-maximum of 4 μs, and the pulse repetition frequency can be changed from single shot to 5 kHz. The main electrical parameters, such as applied voltage, total discharge current, and jet current, are measured. Results show that the intensity and length of jets become stronger and longer as the voltage increases. The discharge current of He plasma jet is only a few millamperes, whereas Ar plasma is hundreds of millamperes. For both cases, the jet speed is on an order of ~10⁴ m/s estimated by the intensified charge coupled device images. The analysis shows that the differences between He and Ar plasma jets are mainly due to the physical and chemical characteristics of Ar and He gases, especially the different ionization energies of particles. In addition, the optical spectrum results show that there are more excited OH radicals and N₂ of the second positive system in Ar plasma jet while the He plasma jet contains more excited O and N₂⁺ of the first negative system.