In this paper, we discuss the results from the two-dimensional computational investigation of the role of thermionic cathode emission in the formation of the negative (reverse) potential near the emissive cathode (LaB6 tablet). Two modes of discharge behavior are considered—high- and low-pressure modes. We show that the region of the negative potential (for that of the emitting cathode) is enclosed in a semi-sphere bounded by the line where the electric field changes its direction. This sheath region was distorted by the movement of the emitting points in horizontal and vertical directions. The unstable behavior of the high pressure discharge and self-excited oscillations of plasma parameters were observed. At low pressure the potential reversal and oscillations were not so pronounced.
In the present study, we computationally investigate the splitting of CO2 to carbon monoxide and oxygen in an atmospheric pressure microwave plasma torch. We demonstrate different stages of CO2 conversion while using 2D and 1D models. For both models, we use identical sets of chemical reactions, cross sections, power profiles and dimensions of the plasma region. Based on the real MW plasma torch device, we first constructed two-dimensional geometry and obtained results using the 2D model. Then, the 1D plug-flow model was employed. With 1D model we expected to obtain the results close to those we already had from the 2D approach. However, we revealed that the gas temperature and plasma species behavior in 1D model was quite different from those obtained with the 2D code. We revisited the 2D results and found that the reverse (upstream) gas flow near the central electrode was responsible for the observed discrepancies. In 2D model, the residence time of a certain portion of gas was much longer. When the flow rate in 1D model was adjusted, the reasonable agreement between both models was achieved.
Plasma mass separation requires a lot of diagnostic techniques that not only demonstrate the separation effect but also show the efficiency of the process. During the test experiments plasma flux to be separated may contain neutral particles that avoid the separation process due to their insensitivity to electromagnetic field. We present the diagnostics of the lost substance that way in experiments on plasma mass separation. Obtained data of the diagnostics helped to determine the law of particle evaporation from the plasma source. We showed that neutral flux is unable to distort the result of separation diagnostics. Presented approach can be used in experiments aimed at enhancing the separation effect and at achieving target productivity for industry applications.
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