IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 6, JUNE 2011
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Study on a Room-Temperature Air Plasma for Biomedical Application ShuQun Wu, Zhan Wang, QuanJun Huang, XinPei Lu, Senior Member, IEEE, and Yuan Pan
Abstract—The I–V characteristics of a room-temperature atmospheric pressure air plasma are investigated. The plasma is driven by a homemade direct-current power supply. However, discharge currents appear pulsed. The pulse behavior is determined by the ion drift mechanism. The effects of the applied voltage and the gap distance d on pulsed repetition frequency f and peak value Ipeak of the current pulse are studied in detail. It is found that the applied voltage dramatically affects Ipeak but not the pulse repetition frequency f . When the applied voltage is higher than 12 kV, the voltage on the electrode just before breakdown starts to decrease with the increase in the applied voltage. A detail analysis shows that the residual charges play an important role in the initiation of breakdown under this condition. On the other hand, when the applied voltage is lower than 12 kV, the voltage on the electrode just before breakdown keeps constant for various applied voltages; it indicates that the residual charges play a minor role in the initiation of breakdown for this circumstance. It is found that the pulse repetition frequency is determined by the time for the ion drift to the electrode. A further analysis shows that the average electric field keeps constant for various gap distances. The pulse repetition frequency is inversely proportional to the gap distance, which is exactly observed in the experiments. Index Terms—Atmospheric pressure plasma, biomedical application, dc discharge, nonequilibrium plasma, plasma jet.
I. I NTRODUCTION
teeth whitening, and so on, it has strict requirements for the safety of the plasma devices. There must have no any harm when the plasmas are touched by human bodies. Fortunately, various plasma jet devices have been recently reported. However, due to diverse applications, plasma jet devices, particularly those using room air as working gas, are still urgent needed. Recently, we have reported a simple atmospheric pressure room-temperature air plasma device [29]. The device can be hand held, and the plasma can be touched by human bodies, without any harm. The total weight of the device, including power supply, is less than 1 kg. In order to characterize the device further, in this paper, the electrical characteristics of the plasma will be studied in detail. The rest of this paper is organized as follows: In Section II, the experimental setup will be described. The experimental results, including the relationship among the applied voltage, pulse frequency, gap distance, and peak value of the pulse current will be reported in Section III. In addition, the simulation results of the current–voltage characteristics will be also presented in Section III. Finally, discussions will be given in Section IV, and Section V provides a brief summary of this paper.
A
TMOSPHERIC pressure nonthermal plasmas (APNPs) are nowadays widely investigated for various applications, such as surface and materials processing [1]–[3], synthesis of nanomaterial [4], [5], and biomedical applications [6]–[14]. Among the applications, the biomedical applications of the APNPs, such as sterilization, are attracting significant attention. For the biomedical applications, plasma jet devices have obvious advantages over the traditional dielectric barrier discharge devices [15]–[28]. However, most of the plasma jet devices reported use noble gases or the mixtures of the noble gases with small amount of O2 as working gases. If ambient air is used as the working gas, the gas temperature of the plasma is normally quite high, which limits the applications of the plasma jet devices. Furthermore, for the applications of plasma medicine, such as wound healing, teeth root-canal treatment, Manuscript received January 27, 2011; revised February 27, 2011; accepted March 15, 2011. Date of publication April 25, 2011; date of current version June 10, 2011. This work was supported in part by the National Natural Science Foundation under Grant 10875048 and Grant 51077063 and in part by the Changjiang Scholars Program, Ministry of Education, People’s Republic of China. The authors are with the College of Electrical and Electronics Engineering, Huazhong University of Science and Technology, Wuhan 430074, 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.2011.2132152
II. E XPERIMENTAL S ETUP The device is driven by a homemade direct-current (dc) lowercase power supply. The output voltage of the power supply can be adjusted up to 20 kV. The output of the power supply is connected to a stainless steel needle electrode through a resistor R of 130 MΩ. The tip of the stainless steel needle has a radius of about 50 μm. Fig. 1(a) and (b) are the schematic of the device and the photograph of the plasma, respectively. Due to the series-connected resistor and the small stray capacitance, the stainless steel needle electrode can be touched by bare hands, without a feeling of electrical shock. The stray capacitance is very small, which is estimated to be about 3.2 pF. Two P6015 Tektronix high-voltage (HV) probes are used to measure the applied voltage and the voltage on the needle, respectively. A TCP202 Tektronix current probe is used to measure the discharge current. III. E XPERIMENTAL R ESULTS When the HV dc power supply is turned on and the distance between the finger and the tip of the needle is within few centimeters, a plasma is generated between the needle and the finger. It is worth emphasizing that there is no transient spark
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Fig. 1. (a) Schematic of the experimental setup and (b) a photograph of the plasma touched by a finger. R = 130 MΩ.
(TS) mode, as observed by Machala et al. [30]. The plasma can always be touched by human bodies, without any harm. This is due to two facts. First, the series-connected ballast resistor R used in our device is much higher than that used by others [30], [31]. Second, the stray capacitance is very small, which is only about 3.2 pF, as previously mentioned. The gas temperature of the plasma is estimated through the emission spectrum of the second positive system of nitrogen. It is at room temperature. Next, the current–voltage characteristics of the plasma will be studied. It is interesting to notice that the discharge is actually pulsed with a frequency in a kilohertz range. It should be pointed out that, when we measure the discharge current, the voltage probe 2 is not used. This is because the probe has an equivalent capacitor of 3 pF, which is on the same order of the stray capacitance. To avoid the interference of the voltage probe 2, the voltage probe 2 is removed when the discharge current is measured. The voltage probe 2 is used only when we measure the voltage on the needle. Certainly, the voltage that we obtained now is different with the voltage when voltage probe 2 is not connected. Nevertheless, the voltage that we obtained from voltage probe 2 will give us some indication about the voltage on the needle. A. Current–Voltage I–V Characteristics for Different Applied Voltages Fig. 2 shows discharge current waveforms for applied voltages of 10, 14, and 18 kV. It clearly shows that the discharge currents appear pulsed. The pulse repetition frequencies f of the discharge currents has small vibrations. However, the pulse repetition frequency for the three applied voltages V1 has no big difference. On the other hand, the peak values Ipeak of the discharge currents strongly depend on the applied voltages. It is about 30 mA for the applied voltage of 18 kV and 12 mA for the applied voltage of 10 kV. To have a clear view of the discharge current pulses, Fig. 3(a) and (b) zoom in the single-current pulses for the applied voltages of 10 and 18 kV, respectively. Moreover, the discharge current, the applied voltage V1 , and the voltage V2 on the needle are also shown on the figures. As shown, the full width half maximum (FWHM) of the discharge
IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 6, JUNE 2011
Fig. 2. Discharge current I waveform for different applied voltage V1 . The gap distance d is fixed at 4 mm.
currents are about 50 ns for both cases. When the discharge ignited, the voltage on the needle drops 100 V for the applied voltage of 10 kV and drops about 600 V for the applied voltage of 18 kV. It is interesting to point out that, for the applied voltage of 18 kV, the voltage on the needle V2 just before breakdown is about 2.9 kV, which is actually lower than that for the applied voltage of 10 kV, as shown in Fig. 3. This can be explained as follows: For the applied voltage of 18 kV, the peak current and the total charge of a single-current pulse is much higher than that of 10 kV. Since the pulse repetition frequency for the two cases has no obvious difference, the residual charge immediately before the discharge ignites for the case of 18 kV is more than that of 10 kV. Thus, the breakdown voltage is lower for the applied voltage of 18 kV. We will point out later that V2 , just before the breakdown for V1 less than 12 kV, keeps a constant. For that case, the residual charge plays a minor role in the breakdown. Regarding the pulse repetition frequency of the discharge current, it is estimated as the following: In the general case, the ion drift mobility can be expressed as [32] 36 1 + M/M i cm2 μi = p[atm] (α/α03 )A V · s where M is the mass of the gas molecule, Mi is the mass of the ion, α/α03 is about 10 for N2 and O2 plasma [32], and A is the molecular weight of the gas. For air plasma, the main ion + is probably N+ 4 , rather than N2 . [32] Therefore, M/Mi = 0.5. For simplicity, assume that it is pure N2 gas; hence, A = 28. In addition, assume that the electric field along the gap is uniform, and we get E = 3 kV/4 mm = 7.5 × 103 V/cm. Therefore, the ion drift velocity υ = μi E = 1.9 × 104 cm/s. In order to have the next current pulse, the N+ 4 has to be removed from the gap. Thus, it takes about 4 mm/υ = 21 μs, which corresponds to a frequency of about 48 kHz. The measured frequency for the applied voltage of 18 kV is about 35 kHz. The difference may be from the estimation of the drift velocity and electric field. To further investigate how the applied voltages V1 affect the pulse repetition frequencies f and the peak value Ipeak
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Fig. 3. Applied voltage V1 , voltage on the needle V2 , and discharge current I waveforms for a single pulse. The applied voltages V1 of (a) 10 and (b) 18 kV. The gap distance d is fixed at 4 mm.
Fig. 4. Relationship between the applied voltage V1 and (a) the pulse repetition frequency f of the current, (b) the peak value Ipeak of the current, and (c) the total charge q of a single current pulse for the gap distance of 4 mm.
of the discharge currents, the pulse repetition frequencies f and the peak value Ipeak of the discharge currents for different applied voltages V1 are measured. Fig. 4(a) and (b) show how f and Ipeak change with V1 for the gap distance of 4 mm. In addition, Fig. 4(c) also shows the relationship between the charge q of a single-current pulse and the applied voltage V1 . As shown in Fig. 4(a), when V1 is lower than 12 kV, the frequency of the pulse current slightly increases with V1 . However, the frequency f stays almost as a constant when V1 is higher than 12 kV. On the other hand, the peak value Ipeak of the pulse current and the total charge of a single-current pulse linearly increase with the applied voltage V1 . Regarding the relationship between the pulse repetition frequency and the applied voltage, there are few points that we would like to discuss next. For applied voltages lower than 12 kV, the pulse repetition frequency of the current increases with the applied voltage V1 . This may be due to the following reasons: As we noticed, when V1 is increased from 8 to 12 kV, the voltage on the needle V2 keeps at about 3.2 kV before the gap breakdown. On the other hand, Fig. 4(c) shows that the charge q of a current pulse significantly increases when V1 is increased from 8 to 12 kV. Fig. 4(a) shows that the pulse repetition frequency for V1 of 12 kV is higher than that of 8 kV. Thus, the concentration of the residual electrons before breakdown for V1 of 12 kV should be higher than that for V1
Fig. 5. Discharge current I waveform for the gap distance d of (a) 3, (b) 5, and (c) 7 mm. The applied voltage V1 is fixed at 18.5 kV.
of 8 kV. However, the breakdown voltage for the two cases is the same. Hence, it can be concluded that the residual electrons play a minor role in the breakdown of the gap for a voltage lower than 12 kV. Since the breakdown voltage is the same for V1 less than 12 kV, the higher the applied voltage, the faster the voltage on the needle reaches the breakdown voltage, the higher the pulse repetition frequency of the current pulse.
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Fig. 6. Applied voltage V1 , voltage on the needle V2 , and discharge current I waveforms for a single pulse. The gap distance of (a) 3 and (b) 7 mm. The applied voltage is fixed at 18 kV.
Fig. 7. Relationship between the gap distance d and (a) the pulse repetition frequency f of the current pulse and (b) the peak value Ipeak of the current pulse for the applied voltage of 18.5 kV.
B. Current–Voltage Characteristics for Different Gap Distances Another parameter that affects the electrical characteristics is the gap distance d. Next, the I–V characteristics of the plasma for different gap distances will be studied. Fig. 5 shows the discharge current waveforms for the gap distances of 3, 5, and 7 mm. As shown, the peak values of the discharge currents have no big difference for the three gap distances. However, the pulse repetition frequencies have an obvious difference. Within the time scale in Fig. 5, there are five, four, and three current pulses for the gap distances of 3, 5, and 7 mm, respectively. Fig. 6(a) and (b) show the I–V characteristics of a single pulse for the gap distances of 3 and 7 mm, respectively. It shows that V2 for the gap distance of 3 mm is about 2.9 kV, and for d = 7 mm, it is about 6.9 kV. Therefore, the average electric field for the two cases is almost the same. Fig. 7(a) and (b) show how the gap distances affect the pulse repetition frequencies and the peak values of the pulse current. With the increase in the gap distance, the pulse repetition frequency significantly decreases. It drops from about 38 kHz for the gap distance of 3 mm to about 7 kHz for the gap distance of 16 mm, as shown in Fig. 7(a). On the other hand, the peak values Ipeak of the pulse current keep as a constant for the gap distance of less than
about 10 mm. It starts to drop when the gap distance is further increased. Regarding the relationship between the repetition frequency and the gap distance, it can be explained based on the ion drift mechanism. As previously pointed out, the average electric field does not depend on the gap distance. Hence, the ion drift velocity ν = μi E should not depend on the gap distance either. Therefore, the time t for N4+ to reach the electrode is equal to d/ν. Thus, the frequency of current pulse f should be inversely proportional to the gap distance. This is exactly observed in Fig. 7(a).
C. Simulation of the Current–Voltage Characteristics In order to better understand the I–V characteristics of the discharge and how the series-connected resistor may affect the plasma behavior, a simple electrical model, as shown in Fig. 8, is used to simulate the I–V characteristics of the device, where R (130 MΩ) is the series-connected resistor, C (3.2 pF) and L (1 nH) are the stray capacitance and the stray inductance, respectively. Rg (100 MΩ) is the effective resistance between the needle and the ground. The plasma is equivalent to Rpg (3.8 MΩ) connected in parallel with Cp (1.1 pF) and Rp
WU et al.: STUDY ON A ROOM-TEMPERATURE AIR PLASMA FOR BIOMEDICAL APPLICATION
Fig. 8. Simple electrical model of the device. The series-connected resistor R = 130 MΩ. The stray capacitance C = 3.2 pF. The effective resistance between the needle and the ground Rg = 100 MΩ. The plasma is equivalent to Rpg (3.8 MΩ) connected in parallel with Cp (1.1 pF) and Rp (85 kΩ).
Fig. 9.
Simulation results of the I–V characteristics of the device.
(85 kΩ). The values of these components are determined when best fit between the experiment and simulation results is obtained. The simulated applied voltage is 18.5 kV. The switch is turned on at a given time so that the simulated current transient corresponds in time with the measurements. Fig. 9 shows the simulation results. They agree with the experimental results very well. However, there is some disagreement between the measured currents and the simulated results. As shown, the simulated current has a wider FWHM than that of the experiment. The difference is due to Rpg , which is treated as a constant in this model. The actual Rpg should be time dependent. It should increase with time after the ignition of the plasma. It is related to the time-dependent resistive behavior of the real plasma. IV. D ISCUSSION Both positive and negative corona discharges have been well studied for many years. When a negative dc voltage is applied to a needle in an electronegative gas such as air, the corona current to a grounded conducting plane can exhibit a time dependence for some range of conditions. The current at corona threshold consists of irregular pulses in the kilohertz range, with a mean current on the order of a microampere. A small increase in voltage results in the establishment of welldefined pulse frequencies, which often extend to a megahertz range. These highly regular current pulses have been studied by
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Trichel, Loeb, and others [33]–[39]. They found out that: 1) the charge per pulse q is comparatively independent of current, needle voltage V , and gap length d; 2) the pulse frequency f is proportional to the voltage above threshold (V − V0 ), where V0 is the corona threshold voltage; and 3) at a constant corona current, the frequency f is independent of the gap length d. Obviously, all these phenomena are different to what we obtained in our experiments. Akishev et al. studied the negative corona and the glow and spark discharges in ambient air and the transition between them [40]. They concluded that diffusive glow discharge (GD) in pin-to-plane corona necessarily occurs before transition to a spark either as a steady-state discharge in airflow or as a transient discharge in static air. As previously pointed out, we do not observe any glow to arc transition under all the tested conditions. Soria-Hoyo et al. simulated the Trichel pulses in pure oxygen by using a particle-in-cell method [41]. According to their simulation results, the existence of stable Trichel pulses is only possible within a certain range of applied voltage. If the maximum voltage is exceeded, the discharge is not stable, and the current intensity exponentially increases in time. On the contrary, if the applied voltage is too low, the current intensity is essentially of nonpulsating nature. When the applied voltage is 2350 V, they observed stable Trichel pulse. The peak value of the current is only about 0.1 mA, and the pulse frequency is approximately 100 kHz. Antao et al. studied the negative dc corona discharges in air, nitrogen, helium, and hydrogen– methane mixtures for a point-to-plate electrode configuration [42]. It is found that, in addition to the bright glow at the cathode (pin) region, a uniform diffuse glow is observed near the anode (plate) surface for the negative corona. This diffuse glow is observed in air and hydrogen–methane discharges only and not in nitrogen discharges. However, they did not observe Trichel pulse behavior. Positive corona discharges, which is similar with our work reported here, have also been investigated [43]–[47]. However, because the series-connected resistor used in our experiments is of orders higher than that used by others and the stray capacitance is only several picofarads, the electrical characteristics of our device reported here are also different to those reported. For example, Machala et al. always observed three discharge modes, i.e., streamer corona (SC), GD, and TS [46], [47]. In their experiments, when an HV of a few kilovolts is applied to a point electrode, SC appears. The SC is typical with small current pulses of streamers (∼10 mA) with a pulse repetition frequency of 10–30 kHz, during which the discharge remains fairly constant and generates cold plasma (∼300 K). This is similar with what we reported in this paper. However, as the voltage is further increased (to ∼8 kV in 6-mm gap), they found out that the streamers establish a conductive channel that leads to a spark formation, with a spark pulse current on the order of ∼1 A. The gas temperature also increases to ∼500–1500 K. The pulse repetition frequency of the pulses is 0.5–5 kHz and increases with the growing applied voltage. This is different with what we observed. For our plasma device, there is no TS discharge mode when the applied voltage was increased to the maximum output voltage (20 kV) of the dc power supply. The gas temperature of our plasma always stays
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at room temperature. In addition, the pulse repetition frequency of the current pulses of our discharges stays approximately at 34 kHz when the applied voltage is higher than 12 kV. Last but not least, the plasma generated by our device can always be touched by human bodies without any feeling of electrical shock or warmth, which is not the case for those reported.
[11]
[12]
V. C ONCLUSION [13]
The I–V characteristics of an atmospheric pressure air plasma driven by a dc power supply have been reported. It is found that the discharge currents actually appear pulsed. The pulse behavior is determined by the ion drift mechanism. The pulse repetition frequency f keeps as a constant when the applied voltage V1 is higher than 12 kV. Moreover, for V1 higher than 12 kV, it is found that, when V1 is increased, the voltage V2 on the needle just before breakdown actually decreases. A further investigation shows that the residual charges play an important role in the initiation of the breakdown under this condition. On the other hand, when V1 is lower than 12 kV, V2 just before breakdown keeps constant for various V1 ; it indicates that the residual charges play a minor role in the initiation of the breakdown for this circumstance. For the gap distance d, the pulse repetition frequencies f strongly depend on d. With the increase in the gap distance, the pulse repetition frequencies significantly decrease. It drops from about 38 kHz for the gap distance of 3 mm to about 7 kHz for the gap distance of 16 mm. The experimental results show that the average electric field keeps constant for various gap distances. The detail analysis shows that the pulse repetition frequency is inversely proportional to the gap distance, which is exactly observed in the experiments. The peak values Ipeak stays at approximately 34 mA when the gap distance is less than 10 mm. It starts to drop only when the gap distance is increased more than 10 mm.
[14]
[15] [16] [17] [18] [19] [20] [21]
[22] [23] [24]
R EFERENCES [1] R. Dorai and J. Kushner, “A model for plasma modification of polypropylene using atmospheric pressure discharges,” J. Phys. D, Appl. Phys., vol. 36, no. 6, pp. 666–685, 2003. [2] D. Mariotti, “Nonequilibrium and effect of gas mixtures in an atmospheric microplasma,” Appl. Phys. Lett., vol. 92, no. 15, pp. 151505-1–151505-3, Apr. 2008. [3] P. Chu, “Plasma-treated biomaterials,” IEEE Trans. Plasma Sci., vol. 35, no. 2, pp. 181–187, Apr. 2007. [4] I. Levchenko, K. Ostrikov, and E. Tam, “Uniformity of postprocessing of dense nanotube arrays by neutral and ion fluxes,” Appl. Phys. Lett., vol. 89, no. 22, pp. 223108-1–223108-3, Nov. 2006. [5] K. Ostrikov, “Colloquium: Reactive plasmas as a versatile nanofabrication tool,” Rev. Mod. Phys., vol. 77, no. 2, pp. 489–511, Apr. 2005. [6] M. Laroussi, “Low temperature plasma-based sterilization: Overview and state-of-the-art,” Plasma Process. Polym., vol. 2, no. 5, pp. 391–400, Jun. 2005. [7] J. L. Walsh and M. G. Kong, “Contrasting characteristics of linear-field and cross-field atmospheric plasma jets,” Appl. Phys. Lett., vol. 93, no. 11, pp. 111501-1–111501-3, Sep. 2008. [8] G. Fridman, A. Brooks, M. Galasubramanian, A. Fridman, A. Gutsol, V. Vasilets, H. Ayan, and G. Friedman, “Comparison of direct and indirect effects of non-thermal atmospheric pressure plasma on bacteria,” Plasma Process. Polym., vol. 4, no. 4, pp. 370–375, May 2007. [9] M. Laroussi, “Low-temperature plasmas for medicine?” IEEE Trans. Plasma Sci., vol. 37, no. 6, pp. 714–725, Jun. 2009. [10] C. Jiang, A. A. Mohamed, R. H. Stark, J. H. Yuan, and K. H. Schoenbach, “Removal of volatile organic compounds in atmospheric pressure air
[25] [26]
[27]
[28] [29] [30] [31]
[32] [33]
by means of direct current glow discharges,” IEEE Trans. Plasma Sci., vol. 33, no. 4, pp. 1416–1425, Aug. 2005. X. Yan, F. Zou, X. Lu, G. He, M. Shi, Q. Xiong, X. Gao, Z. Xiong, Y. Li, F. Ma, M. Yu, C. Wang, Y. Wang, and G. Yang, “Effect of the atmospheric pressure nonequilibrium plasmas on the conformational changes of plasmid DNA,” Appl. Phys. Lett., vol. 95, no. 8, pp. 083702-1–083702-3, Aug. 2009. X. Lu, Z. Xiong, F. Zhao, Y. Xian, Q. Xiong, W. Gong, C. Zou, Z. Jiang, and Y. Pan, “A simple atmospheric pressure room-temperature air plasma needle device for biomedical applications,” Appl. Phys. Lett., vol. 95, no. 18, pp. 181501-1–181501-3, Nov. 2009. P. Bruggeman and C. Leys, “Non-thermal plasmas in and in contact with liquids,” J. Phys. D, Appl. Phys., vol. 42, no. 5, p. 053001, Mar. 2009. X. Lu, T. Ye, Y. Cao, Z. Sun, Q. Xiong, Z. Tang, Z. Xiong, J. Hu, Z. Jiang, and Y. Pan, “The roles of the various plasma agents in the inactivation of bacteria,” J. Appl. Phys., vol. 104, no. 5, pp. 053309-1–053309-5, Sep. 2008. G. Fridman, G. Friedman, A. Gutsol, A. B. Shekhter, V. N. Vasilets, and A. Fridman, “Applied plasma medicine,” Plasma Process. Polym., vol. 5, no. 6, pp. 503–533, Aug. 2008. N. Mericam-Bourdet, M. Laroussi, A. Begum, and E. Karakas, “Experimental investigations of plasma bullets,” J. Phys. D, Appl. Phys., vol. 42, no. 5, p. 055207, Mar. 2009. M. Keidar and I. Belis, “Sheath and boundary conditions for plasma simulations of a Hall thruster discharge with magnetic lenses,” Appl. Phys. Lett., vol. 94, no. 19, pp. 191501-1–191501-3, May 2009. M. Laroussi and X. Lu, “Room-temperature atmospheric pressure plasma plume for biomedical applications,” Appl. Phys. Lett., vol. 87, no. 11, pp. 113902-1–113902-3, Sep. 2005. A. Shashurin, M. N. Shneider, A. Dogariu, R. B. Miles, and M. Keidar, “Temporal behavior of cold atmospheric plasma jet,” Appl. Phys. Lett., vol. 94, no. 23, pp. 231504-1–231504-3, Jun. 2009. X. Lu, Z. Jiang, Q. Xiong, Z. Tang, and Y. Pan, “A single electrode roomtemperature plasma jet device for biomedical applications,” Appl. Phys. Lett., vol. 92, no. 15, pp. 151504-1–151504-3, Apr. 2008. E. Stoffels, I. Kieft, R. Sladek, L. Van den Bedem, E. van der Laan, and M. Steinbuch, “Plasma needle for in vivo medical treatment: Recent developments and perspectives,” Plasma Sources Sci. Technol., vol. 15, no. 4, pp. S169–S180, Nov. 2006. D. Mariotti, V. Svrcek, and D. G. Kim, “Self-organized nanostructures on atmospheric microplasma exposed surfaces,” Appl. Phys. Lett., vol. 91, no. 18, pp. 183111-1–183111-3, Oct. 2007. X. Lu, Y. Cao, P. Yang, Q. Xiong, Z. Xiong, Y. Xian, and Y. Pan, “An RC plasma device for sterilization of root canal of teeth,” IEEE Trans. Plasma Sci., vol. 37, no. 5, pp. 668–673, May 2009. Y. Xian, X. Lu, Y. Cao, P. Yang, Q. Xiong, Z. Jiang, and Y. Pan, “On plasma bullet behavior,” IEEE Trans. Plasma Sci., vol. 37, no. 10, pp. 2068–2073, Oct. 2009. F. Iza, M. G. Kong, and J. K. Lee, “Electron kinetics in radio-frequency atmospheric pressure microplasmas,” Phys. Rev. Lett., vol. 99, no. 7, pp. 075004-1–075004-4, Aug. 2007. G. C. Kim, G. J. Kim, S. R. Park, S. M. Jeon, H. J. Seo, F. Iza, and J. K. Lee, “Air plasma coupled with antibody-conjugated nanoparticles: A new weapon against cancer,” J. Phys. D, Appl. Phys., vol. 42, no. 3, p. 032005, Feb. 2009. J. Kolb, A. Mohamed, R. Price, R. Swanson, A. Bowman, R. Chiavarini, M. Stacey, and K. Schoenbach, “Cold atmospheric pressure air plasma jet for medical applications,” Appl. Phys. Lett., vol. 92, no. 24, pp. 241501-1–241501-3, Jul. 2008. K. H. Becker, U. Kogelschatz, K. H. Schoenbach, and R. J. Barker, NonEquilibrium Air Plasmas at Atmospheric Pressure. Bristol, U.K.: Inst. Phys. Publishing, 2005. S. Wu, X. Lu, Z. Xiong, and Y. Pan, “A touchable pulsed air plasma plume driven by dc power supply,” IEEE Trans. Plasma Sci., vol. 38, no. 12, pp. 3404–3408, Dec. 2010. Z. Machala, E. Marode, C. O. Laux, and C. H. Kruger, “DC glow discharges in atmospheric pressure air,” J. Adv. Oxid. Technol., vol. 7, no. 2, pp. 133–137, Jul. 2004. X. Meng, H. Zhang, and J. Zhu, “A general empirical formula of current–voltage characteristics for point-to-plane geometry corona discharges,” J. Phys. D, Appl. Phys., vol. 41, no. 6, pp. 065209-1–065209-10, Mar. 2008. Y. P. Raizer, Gas Discharge Physics. Berlin, Germany : Springer-Verlag, 1991. G. W. Trichel, “The mechanism of the negative point to plane corona near onset,” Phys. Rev., vol. 54, no. 12, pp. 1078–1084, Dec. 1938.
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[34] L. B. Loeb, A. F. Kip, G. G. Hudson, and W. H. Bennett, “Pulses in negative point-to-plane corona,” Phys. Rev., vol. 60, no. 10, pp. 714–722, Nov. 1941. [35] L. B. Loeb and J. M. Meek, “The mechanism of spark discharge in air at atmospheric pressure. II,” J. Appl. Phys., vol. 11, no. 7, pp. 459–474, Jul. 1940. [36] L. B. Loeb, Electrical Coronas. Berkely, CA: Univ. California, 1965. [37] W. L. Lama and C. F. Gallo, “Systematic study of the electrical characteristics of the ‘Trichel’ current pulses from negative needle-to-plane coronas,” J. Appl. Phys., vol. 45, no. 1, pp. 103–113, Jan. 1974. [38] C. Sang, J. Sun, C. Ren, and D. Wang, “Characteristics of nanosecond pulse needle-to-plane discharges at high pressure: A particle-incell Monte Carlo collision simulation,” J. Appl. Phys., vol. 105, no. 4, pp. 043305-1–043305-6, Feb. 2009. [39] J. Paillol, P. Espel, T. Reess, A. Gibert, and P. Domens, “Negative corona in air at atmospheric pressure due to a voltage impulse,” J. Appl. Phys., vol. 91, no. 9, pp. 5614–5621, May 2002. [40] Y. Akishev, M. Grushin, I. Kochetov, V. Karal’nik, A. Napartovich, and N. Trushkin, “Negative corona, glow and spark discharges in ambient air and transitions between them,” Plasma Sources Sci. Technol., vol. 14, no. 2, pp. S18–S25, May 2005. [41] C. Soria-Hoyo, F. Pontiga, and A. Castellanos, “Particle-in-cell simulation of Trichel pulses in pure oxygen,” J. Phys. D, Appl. Phys., vol. 40, no. 15, pp. 4552–4560, Aug. 2007. [42] D. S. Antao, D. A. Staack, A. Fridman, and B. Farouk, “Atmospheric pressure dc corona discharges: Operating regimes and potential applications,” Plasma Sources Sci. Technol., vol. 18, no. 3, p. 035016, Aug. 2009. [43] S. Pekarek, V. Kriha, M. Simek, R. Balek, and F. Hanitz, “Hollow needleto-plate electrical discharge at atmospheric pressure,” Plasma Sources Sci. Technol., vol. 8, no. 3, pp. 513–518, Aug. 1999. [44] D. Dubois, N. Merbahi, O. Eichwald, M. Yousfi, and M. Benhenni, “Electrical analysis of positive corona discharge in air and N2 , O2 , and CO2 mixtures,” J. Appl. Phys., vol. 101, no. 5, pp. 053304-1–053304-9, Mar. 2007. [45] K. H. Schoenbach, A. Ei-Habachi, W. Shi, and M. Ciocca, “High-pressure hollow cathode discharges,” Plasma Sources Sci. Technol., vol. 6, no. 4, pp. 468–477, Nov. 1997. [46] Z. Machala, I. Jedlovsky, and V. Martisovits, “DC discharges in atmospheric air and their transitions,” IEEE Trans. Plasma Sci., vol. 36, no. 4, pp. 918–919, Aug. 2008. [47] Z. Machala, I. Jedlovsky, L. Chladekova, B. Pongrac, D. Giertl, M. Janda, L. Sikurova, and P. Polcic, “DC discharges in atmospheric air for biodecontamination—Spectroscopic methods for mechanism identification,” Eur. Phys. J. D, vol. 54, no. 2, pp. 195–204, Aug. 2009.
ShuQun Wu received the B.E. degree in electrical engineering in 2010 from the Huazhong University of Science and Technology, Wuhan, China, where he is currently working toward the Ph.D. degree in the College of Electrical and Electronic Engineering. His research interests are focused on the diagnostics and applications of atmospheric pressure nonequilibrium plasma sources.
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Zhan Wang, photograph and biography not available at the time of publication.
QuanJun Huang, photograph and biography not available at the time of publication.
XinPei Lu (M’06–SM’07) received the Ph.D. degree in electrical engineering from the Huazhong University of Science and Technology, Wuhan, China, in 2001. From 2002 to 2006, he worked at Applied Plasma Technology Laboratory, Old Dominion University, Norfolk, VA, as a Research Associate. In 2007, he joined Huazhong University of Science and Technology, where he is currently a Professor (Changjiang Scholar) with the College of Electrical and Electronic Engineering. He is the author or coauthor of about 60 scientific articles in these areas. His research interests include low-temperature plasma sources and their applications, modeling of lowtemperature plasmas, plasma diagnostics, and pulse power technology. Dr. Lu has also served as a Guest Editor of the IEEE T RANSACTIONS ON P LASMA S CIENCE and as the Session Chair at the International Conference on Plasma Science for several years.
Yuan Pan received the B.S. degree in electrical engineering from the Huazhong University of Science and Technology, Wuhan, China, in 1955. He has worked with the Institute of 401, the Institute of 585, the Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China, the Joint European Tokamak, and the Fusion Center of University of Texas, Austin. He is currently a Professor and the Honorary Dean of the College of Electrical and Electronic Engineering, Huazhong University of Science and Technology. He is the author or coauthor of about 100 scientific articles in these areas. His main research interests include magnetic confinement nuclear fusion, high-power pulse source technology, superconducting electric power, and pulse power technology. Mr. Pan is a member of the Chinese Committee of Experts of International Thermonuclear Experimental Reactor. He was elected as a member of the Chinese Academy of Engineering in 1997.
