Dynamics of Mode Transition in Air Dielectric Barrier ... - IEEE Xplore

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S. Wu, Zhan Wang, Quanjun Huang, Wei Wang, S. Yu, Changlin Zou, Yan Lu, and Xinpei Lu. Abstract—In general, parameter pressure × gap distance. (p × d) in ...
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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 42, NO. 10, OCTOBER 2014

Dynamics of Mode Transition in Air Dielectric Barrier Discharge by Controlling Pressures S. Wu, Zhan Wang, Quanjun Huang, Wei Wang, S. Yu, Changlin Zou, Yan Lu, and Xinpei Lu

Abstract— In general, parameter pressure × gap distance ( p × d) in dielectric barrier discharge is used to control the electrical breakdown and plasma characteristics. In this paper, we investigate the critical pd value for air discharge transition from filamentary to homogeneous mode by controlling the pressure. Dynamics of the air discharge show that the discharge transits from filamentary to homogeneous mode when the operating pressure decreases from 9 to 4 kPa. With 1-mm thickness alumina applied pulsed power, the critical pd value obtaining homogeneous air plasma is 40 kPa mm. Index Terms— Air plasma, dielectric barrier discharge, filamentary and homogeneous plasmas

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IELECTRIC barrier discharge (DBD) usually manifests as a filamentary streamer discharge in atmospheric air [1], [2]. The DBD in filamentary mode has some disadvantages in material surface treatment for high-density spots on the surface of material to be treated, causing inhomogeneous treatment or local damage, which limits its industrial application prospect. Therefore, DBD in homogeneous mode at atmospheric pressure is urgently needed for material surface treatments. For the big challenge of generating homogeneous air DBD at atmospheric pressure, we investigate the characteristics of air DBD by controlling the pressure. The DBD are generated between two circular electrodes with diameter of 70 mm. Both electrodes are covered by a alumina plate with a thickness of 1 mm. The discharge gap is fixed at 10 mm for all experiments. The upper electrode is connected to the pulsed power supply (amplitude up to 10 kV, repetition frequency up to 10 kHz, and pulsewidth variable from 200 ns to dc), the lower electrode is grounded. The DBD

Manuscript received November 1, 2013; revised May 11, 2014; accepted June 6, 2014. Date of publication June 27, 2014; date of current version October 21, 2014. This work was supported in part by the National Natural Science Foundation under Grant 51077063 and Grant 51277087, in part by the Graduate Innovation Foundation, Huazhong University of Science and Technology, Wuhan, China, under Grant 0109070085, and in part by the Natural Science Foundation of Anhui University, Hefei, China, under Grant KJQN1104. S. Wu, W. Wang, S. Yu, C. Zou, and X. Lu are with the State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074, China (e-mail: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]). Z. Wang and Q. Huang are with the Aviation Key Laboratory of Science and Technology on Stealth Technology, Shenyang 110035, China (e-mail: [email protected]; [email protected]). Y. Lu is with the School of Physics and Material Science, Anhui University, Hefei 230039, China (e-mail: [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2014.2330360

Fig. 1. Photos of the air DBD under different pressures. Electrical parameters of applied pulse voltage: pulse amplitude of 3.5 kV, pulsewidth of 800 ns, and pulse frequency of 5 kHz. These photos are captured by a Sony digital camera with an exposure time of 1 s.

device is placed in a closed chamber, connected to a rotary pump (Oerlikon Leybold: D16C). The operating pressure can be adjusted from 1 Pa to atmospheric pressure. Fig. 1 shows the air plasma in DBD for different pressures. The discharge is filamentary for pressure of 9.5 kPa, then it turns into filamentary-homogeneous mixed mode for pressure of 8.5 kPa, finally homogeneous air plasma is achieved as the pressure is further reduced to 4 kPa. To further investigate the mode transition of the air DBD, dynamics of the air DBD are captured by a intensified charge-couple camera device (Princeton Instruments, Model: PIMAX2, exposure time down to 0.5 ns). Figs. 2(a) and (b) shows the high-speed images of air plasma for pressures of 9 and 4 kPa, respectively. When the pressure p = 9 kPa is used, two air plasma filaments are ignited at 3 ns, then propagating toward both axial and radial directions, which leads to the cross section of filaments increasing, as shown in Fig. 2(a). At 842.5 ns, it is interesting to observe that a relative homogeneous air plasma is ignited at the middle of the discharge gap rather than the surface of electrodes, propagating and reaching the lower electrode at 847.5 ns, and then it develops and strikes the upper electrode in turn at 852.5 ns. On the other hand, Fig. 2(b) shows the dynamic of homogeneous air discharge for pressure of 4 kPa. In both discharges at the pulse rising and falling time, homogeneous air plasma is ignited at the surface of upper electrode, propagating and hitting the lowerelectrode. In addition, it is noteworthy to point out that a relative bright column remains in the middle of the gap at 877.5 ns, which is opposite with the results for pressure of 9 kPa at 877.5 ns in Fig. 2(a).

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WU et al.: DYNAMICS OF MODE TRANSITION IN AIR DBD

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Fig. 2. High-speed images of the discharge for (a) 9 kPa and (b) 4 kPa. Each image is captured at the same delay time with a single shot. Exposure time is fixed at 2.5 ns. Time labels on each image correspond to the pulse rise edge of applied pulse voltage. Other parameters are the same as that in Fig. 1.

Regarding the mode transition in air DBD at operating pressure of 4 kPa, the value of critical pd is 40 kPa mm for the 1-mm thick alumina as dielectric material, which is one order higher than that in [3] and [4]. For example, Choi et al. [3] reported that the critical pd for air DBD transition from filamentary to homogeneous mode is 1.3-kPa mm with 1-mm thickness alumina applied ac power. Because homogeneous air plasma can be easily produced by applied pulse voltage with fast rising edge, we believe that the applied pulse voltage with 60-ns pulse rising and falling time rather than approximately kilohertz ac voltage should be responsible for the higher critical pd value herein than that reported in [3]. In addition, because the surface charge accumulation depends on the conditions of the surface, such as roughness or secondary emission coefficient, the different surface condition of alumina plate may be also the reason for high-critical pd value. Based on the pd scaling law, if we use 1-mm thick alumina as dielectric material at atmospheric pressure, the air gap distance for generating a homogeneous

plasma is about 0.4 mm. Such small distance limits the size of samples to be treated. More experimental studies to analyze the discharge behavior of microgap DBD are needed for generating homogeneous air plasma at atmospheric pressure. R EFERENCES [1] U. Kogelschatz, “Dielectric-barrier discharges: Their history, discharge physics, and industrial applications,” Plasma Chem. Plasma Process., vol. 23, no. 1, pp. 1–46, 2003. [2] H.-E. Wagner, R. Brandenburg, K. V. Kozlov, A. Sonnenfeld, P. Michel, and J. F. Behnke, “The barrier discharge: Basic properties and applications to surface treatment,” Vacuum, vol. 71, no. 3, pp. 417–436, 2003. [3] J. H. Choi et al., “Investigation of the transition between glow and streamer discharges in atmospheric air,” Plasma Sources Sci. Technol., vol. 15, no. 3, pp. 416–420, 2006. [4] Z. Fang, J. Lin, X. Xie, Y. Qiu, and E. Kuffel, “Experimental study on the transition of the discharge modes in air dielectric barrier discharge,” J. Phys. D, Appl. Phys., vol. 42, no. 8, p. 085203, 2009.