Numerical Study On Discharge Structures Of RF Argon Glow Discharges At Low Pressure In Thin Long Tube

With the constant development of industrial technology,the demand for materials is also higher and higher in modern life.In order to adapt to high hardness,high toughness,heat shock resistance,wear resistance,resistance to acid and alkali corrosion,and all other special requirements,all kinds of researches have been done and are being done to develop a variety of new metal materials.These special metal materials are relatively expensive,therefore,people try to use a variety of surface modification technology on the ordinary metal materials to change its surface properties to meet the complex requirements.Due to corrosion,wear and other common problems are first occurred on the metal surface,surface modification treatment can greatly improve the metal material life.Surface modification in metal tube can improve the hardness,wear resistance,corrosion resistance of the inner surface of metal tube.It has great potential for application in industrial practice.The inner surface modification can be achieved by using glow discharge process in metal tube.Glow discharge plasma process accords with modern environmental protection,and the cost of device and maintenance is low.In order to increase the utilization efficiency of plasma in metal tube,it is necessary to study systemically in details of the discharge structures.Hence,based on the plasma fluid theory and using the drift-diffusion approximation,a one-dimensional fluid model of RF argon glow discharges at low pressure in a thin long tube is established for studying discharge structures.In this paper we have mainly studied for two aspects.In the first part of this work,by means of systematic analysis of the results,we obtained the evolution characteristics of the discharge structures under 1Torr in thin long tube.Numerical results show that,with the increasing discharge time,the sheath width increases gradually and the discharge asymmetry strengthens slowly.Moreover,the raising of the cycle-averaged electron density and the dropping of the cycle-averaged ion density occur around the powered electrode,which is related to the reversed electric field during powered electrode sheath collapsing.Compared with the potential drop in grounded electrode sheath,the drop in powered electrode sheath is steeper due to the smaller electrode area.Hence,the electron temperature is higher in the powered electrode sheath.Also,we can observe that the ionization mainly occurs in bulk-plasma under the current parameter conditions.With the increasing discharge time,the ionization in bulk-plasma weakens gradually.In the second part of this work,we studied systematically the neutral gas pressure,voltage peak,RF frequency,powered electrode radius,tube inner radius effects on the physical characteristics of the discharge structures.Numerical results show that,while the neutral gas pressure increases from 0.2Torr to 10 Torr,the discharge asymmetry strengthens gradually and the relative intensity of reversed electric field weakens slowly.Driving power parameter changes imply that the discharge asymmetry is almost kept unchanged,neither by the changes of the voltage peak(from 60 V to 200V)nor by the RF frequency(from 5MHz to 40MHz).The relative intensity of reversed electric field becomes weaker in bigger voltage peak and stronger in higher RF frequency.As applied voltage peak is increasing,the sheath widths slightly increase,but the change is opposite with increasing RF frequency.Geometric dimension scans show that,the small powered electrode radius and the large tube inner radius will be beneficial to the increased plasma density,but the discharge symmetry is opposite.The relative intensity of reversed electric field weakens obviously and the ionization in bulk-plasma strengthens gradually accompanied with the powered electrode radius increases from 0.01 cm to 0.10 cm.However,as the tube inner radius is increasing from 0.35 cm to 0.70 cm,the relative intensity of reversed electric field increases slightly and the ionization in bulk-plasma weakens gradually.The results of this paper have some guiding significance for the surface modification of the tube inner wall.