Numerical Study On The Gas Temperature Of Atmospheric Pressure Pulse-modulated Radio-frequency Discharge

Recently, there have been increased interests in non-thermal atmospheric pressure plasmas because of the capability to produce reactive species without expensive vacuum systems. Among kinds of the power sources, the ratio-frequency (rf) power is almost the favorite one due to its advantage such as lower breakdown voltage, higher reactive spices density, and easier to achieve uniform glow plasmas. However, its applications were restricted owing to the relatively higher gas heating as compared with low frequency discharges, pulse-modulated rf plasmas at high pressures have drawn intensive attention because they possess not only the trait of high density of reactive species of rf voltage power sources but also good control of plasma parameters, particularly of overheating. Then, the discharge characteristics varying with modulated pulse frequencies and pulse widths were studied experimentally and numerically in helium, respectively. Some other works were also carried out such as self-organized patterns and the metastable particles in this discharge apparatus. Recently, several groups claimed that pulse-modulation of the rf power could significantly change the gas temperature (T_g).In this paper, the T_g characteristics in the pulse-modulated rf glow discharge at atmospheric pressure conditions was investigated with a one-dimensional two temperature fluid model. The spatiotemporal graph of the T_g in consistent rf and pulse-modulated rf discharge was shown comparatively then the Te feature was described. Additionally, the influences of the duty cycle on the discharge parameters were studied. Finally, the discharge mode changed from α to γ mode in the pulse-modulated rf discharge was investigated。 dielectric barriers are another way get lower gas temperature, and makes a compared study between the rf dielectric barrier discharge and rf glow discharge.The T_g in the pulse-modulated radio-frequency (rf) glow discharge was investigated in this paper. This study shows that T_g can be controlled effectively by the in-consistent pluse-modulated rf driven power; The internal mechanisms controlling it were given, and after the power is off, Te drops abruptly but T_g is likely to continue for some time, because the relatively small mass compared to the ions. The influences of the duty cycle on the discharge parameters were also studied. When the duty cycle is fixed, the pulse frequency is another factor to control the T_g, and the smaller the value of pulse frequency is, the smaller the value of T_g is, at the same time T_g decreases almost linearly with the reduce of the duty cycle, and it exists one ideal value of the duty cycle by which both the lower gas temperature and the glow mode could be achieved. The reason is revealed in this study, the following conclusion is provided, T_g is determined by the rate of energy transfer from electrons to the neutral gas through elastic collision and the ion Joule heating. The modulation by the pulse power makes each energy source terms reduced obviously and not much difference is found on their response reduction. We also study the transition from the α to γ mode in the pulse-modulated radio-frequency (rf) glow discharge. The ion Joule heating plays a key role in the transition from the a to y mode, there is an obvious change in the spatial distribution of T_g. Specifically, the peak value of T_g appears on the boundary in y mode, and the peak value of T_g in the central region of discharge is larger in a mode, and the rf dielectric barrier discharge can obtain lower temperature under the same conditions.