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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 36, NO. 4, AUGUST 2008
A Cold Plasma Jet Device With Multiple Plasma Plumes Merged XinPei Lu, Senior Member, IEEE, Qing Xiong, ZhiYuan Tang, ZhongHe Jiang, and Yuan Pan
Abstract—As nonthermal atmospheric pressure plasmas come to play an important role in diverse applications, reliable and arcing-free low-temperature plasma sources are needed urgently. In this paper, a low-temperature plasma jet device, which generated four plasma plumes simultaneously, is developed. The plasma jet device can be driven by pulsed dc or kilohertz ac power supply. There is no risk of arcing. When the plasma plumes are contacted with a conductive surface, the four plasma plumes merge together and form a uniform plasma layer on the surface of conductive material with an area of about 1 cm2 . The gas temperature of the plasma plumes is close to room temperature. Index Terms—Atmospheric pressure plasma, decontamination, dielectric barrier discharge, nonequilibrium plasma, nonthermal plasma, plasma jet, surface modification.
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TMOSPHERIC pressure plasmas received great attention recently due to several novel applications such as surface modifications of polymers, absorption and reflection of electromagnetic radiation, and biological and chemical decontaminations of media [1]–[4]. However, under one atmospheric pressure, because of relatively high breakdown voltage of working gases, the discharge gaps are normally in a range from few millimeters to several centimeters, which limits the size of samples to be treated. Moreover, some materials may affect the plasma stability when they are put in the discharge gap. If remote exposure (when the material is put outside the discharge gap, by flowing the gas from the discharge gap to the material surface, the material is treated by the afterglow of the plasma) is used, some short lifetime active species may already disappear before reaching the samples. To address these concerns, cold atmospheric pressure plasma jets (C-APPJ) are attracting a lot of attention recently [5]–[11]. Because of the merit of the plasma jets, which generate plasmas in an open space (surrounding air) rather than confined in discharge gaps only, many potential applications become possible, such as surface decontamination of temperature-sensitive object with large size.
Manuscript received February 23, 2008; revised March 8, 2008. This work was supported by the Chang Jiang Scholars Program, Ministry of Education, China. The authors are with the College of Electrical and Electronic Engineering, HuaZhong University of Science and Technology, Wuhan 430074, China (e-mail:
[email protected]). Digital Object Identifier 10.1109/TPS.2008.922441
On the other hand, for most of the plasma jet devices, the diameters of the plasma plumes are within the range of few millimeters, which makes it difficult for applications such as decontamination of objects with large surface area. In this paper, a specially designed plasma jet device is reported. The schematic of the device is shown in Fig. 1(a). It is made of an alumina tube, which consists of four through holes. The diameter of the alumina tube is 10 mm. The diameter of each hole is 2 mm. The distance between the centers of the nearby holes is 3 mm. The two ring electrodes are made of aluminum foil. The distance between the two ring electrodes is variable from several millimeters to several centimeters. When a pulsed dc voltage or an ac voltage operating in the range of kilohertz is applied to the two ring electrodes, and working gas, such as helium, argon, nitrogen, or their mixtures with a small amount of air, is injected from the left side of the four holes with a total flow rate of several liters per minute, four plasma plumes are generated simultaneously with their length up to 4 cm long. When the plasma plumes are contacted with a conductive surface, the four plasma plumes merged together and form a uniform plasma layer on the surface of the conductive material. The merge area of the plasma layer is about 1 cm2 , as shown in Fig. 1(b). In addition, we are able to operate several of these plasma jet devices in parallel with one power supply. Hence, it is possible to generate large area APPJs with this device. The gas temperature of the plasma plumes, which is very close to the rotational temperature of nitrogen (nitrogen is diffused from the surrounding air), is determined by analyzing the rotational structure of the nitrogen second positive system emission. With helium as working gas, when pulsed dc voltages are used, the gas temperature of the plasma plume is close to room temperature for the applied voltage of 5 kV, the pulse frequency of 1 kHz, and the pulsewidth of 1 µs. On the other hand, the gas temperature is increased to about 50 ◦ C when the 40-kHz ac power supply is used with a voltage of 5 kV (rms). To identify the various reactive species generated by the plasma plumes, optical emission spectroscopy is applied in the 200–1200-nm wavelength range (Princeton Instruments Acton SpectraHub 2500i). The optical emission spectra are dominated by OH, O, NO, N2 , and N+ 2 transitions. As we know that species such as OH and O are very reactive, therefore this device may be suitable for applications such as the surface modification of temperature-sensitive material and the biological and chemical decontaminations of media.
0093-3813/$25.00 © 2008 IEEE
LU et al.: COLD PLASMA JET DEVICE WITH MULTIPLE PLASMA PLUMES MERGED
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Fig. 1. (a) Schematic of the plasma jet device. Diameter of the alumina tube: 10 mm; diameter of each hole: 2 mm; distance between nearby holes: 3 mm. (b) Photo of the plasma jet with four plasma plumes merged together (working gas: helium; flow rate: 6 l/min; applied voltage: 5 kV (rms); ac frequency: 40 kHz).
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