Investigation Of Pulse Discharge Under Low Air Pressure

Recently, atmospheric pressure pulse discharge plasma jet has become one of the hotspots in the field of plasma science and technology. Even though the researchers have done a lot of work to explain the mechanism of plasma propagation, but still fail to reach a unanimous agreement. Most of the existing researches are focus on the atmospheric pressure gas discharge, as to the low pressure pulse discharge are still not well studied. In order to further improve the related theory of plasma jet propagation, from the view of pressure and gases, this paper studied the basic characteristic of the pulse discharge plasma under low pressure systematically.Firstly, this article studied the basic characteristic of the discharge plasma under different pressure systematically. Graphically, improved the gas pressure from 15 Pa to 5000 Pa, similar to the characteristics of Paschen's law, the difficulty of the discharge have been decreased firstly and then increased, which can be explained by Townsend breakdown mechanism. When the pressure reached 5000 Pa or above, space charge and surface charge, which resulted in the surface discharge or even unstable discharge, played a important role in gas discharge. From the view of plasma propulsion form, the plasma move forward in the form of columnar when the air pressure is between 20 Pa and 500Pa; when the pressure is between 500 Pa and 5000 Pa, during the propulsion process of the plasma, the head of the plasma will separate from the high voltage electrode, and the plasma head is in bullet shape. Otherwise, the discharge turns out to be unstable. From the view of plasma velocity, when the pressure is between 30 Pa and 5000 Pa, the plasma propulsion is at speed of 105~107m/s in the rising edge discharge. And maximum speed is obtained when the pressure is 100 Pa which is up to 6×106m/s. Research indicates that the plasma propulsion at this high speed is mainly based on electron impact ionization and photon-ionization under the low pressure. Then, by comparing the pulse discharge development process of nitrogen, oxygen and air under the same pressure, we found that nitrogen and oxygen discharge turn into unstable discharge when the pressure is 1000 Pa and 2000 Pa, respectively. After the pressure over than 1000 Pa, the plasma propulsion speed of nitrogen discharge will be significantly slower than air and oxygen, and it also has a shorter discharge length. Besides, this paper also discussed the effects of the power parameters on the development of these three kinds of gas discharge, and found that the change of the frequency and pulse width separately has a big different impact on the plasma development under different pressure.