Two-dimensional Numerical Study Of Cold Atmospheric Pressure Plasma Jet With Needle-ring Electrodes

In recent years, the atmospheric pressure plasma jet (APPT) has received extensive attention due to its advantages. Different from traditional source of low temperature plasma, atmospheric pressure plasma jet has successfully separated the gas discharge areas and working regions. Under the influences from gas flow and electric field, the various active species such as radicals, charged species, ultraviolet, excited species and metastable species produced during the discharge can be delivered to remote locations, so it can separate the space of plasma generation from their working regions, and it also can simultaneously achieve both high discharge stability and efficient reaction chemistry. In addition, APPJ comes with no electrical or thermal shocks, which makes it impossible for plasma jet to contact with living organisms directly, bringing breakthrough to both traditional industrial applications and the biomedical field. In this article, based on two-dimensional axisymmetric plasma fluid model, we use COMSOL software to simulate atmospheric pressure helium plasma jet.Electrode structure has important effect on the propagation of the plasma jet. Plasma jets driven by different electrode structures have various dynamic characters. It is essential to obtain nice dynamic characters of plasma jet by changing electrode structures. In the third chapter of this paper, we numerically simulate the situation of the propagation of the plasma jet under three different electrodes. The three electrodes are respectively:the first electrode structure has only one needle electrode, and the needle is forced by positive voltage; The second electrode structure has both needle electrode and ring electrode, and they are both forced by positive voltage; The third electrode structure also has both needle electrode and ring electrode, the needle electrode is forced by positive voltage, but the ring electrode is grounding electrode. The positive voltage is pulse voltage, and we only simulate the situation of the propagation of the plasma jet in one cycle. We compare the electron density, electron temperature, jet velocity, the ionization rate and the electric field under different electrodes to analyze the dynamic characters of plasma jet, which can make plasma jet a better application in both industrial and medical fields. We found that the plasma jet forced by the third electrode had higher density, stronger electric field and faster speed, which can illustrates the plasma jet with the third electrode has better dynamic characters.In the fourth chapter of this paper, we study the influence of the dynamic characters of the plasma jet by applying magnetic field. The magnetic field of the discharge device in the direction of axis is respectively 0 T,0.2 T,0.4 T,0.6 T. By comparing the differences of the electron density, ionization rate, electron temperature, electric field and the propagation speed of the plasma jet, we analyze the effect of the applied magnetic field on the propagation of the plasma jet. The study found that the applied magnetic field could change the dynamic behavior of the plasma jet. For example, it can increase the electron density and electric field of plasma jet. Plasma jet's electron density becomes larger and electric field becomes stronger by increasing the applied magnetic field. Electron will move along the magnetic field line due to the effect of the applied magnetic field, which increases the probability of particle collisions with neutral particles in the medium tube. In addition, the magnetic field can confine charged particles. Therefore, when the jet propagates to the outside of the tube, we can obtain larger electron density, stronger electric field and longer propagation distance. We also find a new way to improve electron density and the size of the jet.