Numerical Study On Plasma Characteristics In DC Discharge Under Low Gas Pressure In A Thin Long Tube

In recent years, the technology of plasma surface modification is widely in demand in many areas. However, treating the inner surface of tubes by the same processing has encountered difficulties, especially for inner surface modification in thin long tubes. In order to process efficiently inner surface modification in thin long tubes by means of this technology, the physical problems of plasma in a thin long tube need to be researched. For the studies on these problems, numerical simulation is a convenient and economic way. A study on numerical simulation of the plasma generation and its characteristic in thin long tubes has been performed in this paper, and for the material inner surface modification of the thin long tube, the simulation results would have a good theoretical significance.In this paper, we take the plasma which is produced by DC discharges in argon, under low pressure in a thin long tube, as the research object, consider ionization, and use drift-diffusion approximation in one-dimensional cylindrical coordinate system to establish mathematical model. The corresponding difference equations are obtained by using finite difference method. The evolution of electron density, ion density, electron temperature, ionization, potential and electric field, have been obtained. The effects on the plasma generation and its characteristics by changing applied voltage, gas pressure, electrode radius and tube radius are analyzed, with other parameters unchanged. Meanwhile, with different tube radiuses, the effects on the plasma distributions by changes of applied voltage, gas pressure and electrode radius are also studied in the range of 0.1cm near the tube.According to the research, the discharge reaches steady state, under the parameters in our study. The distributions of electron density and ion density in the tube are almost same and all uneven. A uniform plasma density region is formed in the middle of the electrode and the tube.The plasma sheath is formed near the electrode, where potential drop is seen obviously. Outside the plasma sheath region, the distribution of electron density and ion density are almost same, and potential and electric field are constant. Ionization occurs mainly in the middle of the electrode and the tube.The impacts on region of uniform plasma can be seen by changing the applied voltage, gas pressure and tube radius, with other parameters unchanged. The distribution of plasma characteristics is different at different tube radius near the tube.