Figure
1.
Schematic diagram of the experimental setup.
| Citation: |
Jiaxin LI, Zhengchao DUAN, Feng HE, Ruoyu HAN, Jiting OUYANG. Influence of the pulse polarity on micro-hollow cathode helium plasma jet[J]. Plasma Science and Technology, 2023, 25(7): 075401. DOI: 10.1088/2058-6272/acb489
|
Helium plasma jets generated by micro-hollow cathode discharge (MHCD) with the square-wave power source of different polarities are investigated in this work. The effects of positive and negative polarity pulses on the MHCD and plasma jet were compared, and the time-resolved optical emission spectra of excited species (N2+ and O) were studied. The results confirm that the electric field is a key factor for the propagation of the jet during the rising edge of the positive current pulse, while the gas expansion is mainly important for the jet propagation during the current stable phase. The time-resolved spectra show that the generation of specie O in the jet-driven by the electric field is more efficient.
Atmospheric pressure plasma jet (APPJ) is a low-temperature non-equilibrium plasma generated in an open environment outside the discharge region, which has broad application prospects in material processing, nanomaterial growth, biomedicine, and so on [1–5]. During the last decade, the APPJ has become a highlight topic pursued in the field of low-temperature plasma.
The characteristics of APPJ are influenced by discharge configuration, working gas, and driving scheme. Typical APPJs are generated by needle electrode, dielectric barrier discharge or micro-hollow cathode configuration within gas He/Ar [1, 6–8]. Some temporal evolution photographs of the plasma jet obtained by intensified charge-coupled device (ICCD) camera show that a continuous plasma jet observed by the naked eye is actually composed of a moving plasma bullet or a guided ionization wave [9–15]. The propagation velocity of the plasma bullet estimated from the time-resolved results is on the order of 104–105 m s-1, which is much larger than the velocity of gas flow (about 10–100 m s-1) [10–13]. Mericam-Bourdet et al also observed the on-axis images of the plasma jet and found that the plasma bullet propagating in the air is actually a hollow structure, similar to a 'doughnut' [11]. The propagation dynamics of those plasma jets is considered to be a cathode-directed streamer with photo-ionization or a solitary ionization surface wave [10–12].
The APPJ can be excited by direct current (DC), alternating current (AC), radio frequency (RF), and microwave power supplies. Comparing with continuous wave operation, the pulsed operation can provide more parameters to control the temperature, energy efficiency, and reactive species of plasma jet [16–19]. The pulse polarity is also an important factor for plasma jet. The APPJs excited by the pulses with positive polarity have longer plume, faster propagation speed, and more excited species, than the negatively excited APPJs [12, 16, 20, 21], and the results are attributed to the direction of the applied electric field. The propagation of plasma bullet was observed in a jet of positive polarity pulse, whereas in a jet of negative polarity pulse, a more continuous plasma is observed [12, 20–22]. Some researches also show that the jets of positive and negative polarity pulses can produce different reactive species and have different effects on cell [23].
The concept of micro-hollow cathode discharge (MHCD) was developed originally by Schoenbach et al [24]. The electrode gap in MHCD is less than 1 mm; therefore the igniting and sustaining voltage of the micro-hollow cathode is very low [25]. Using a micro hollow cathode, Hong et al obtained an air plasma jet with ~3 kV negative pulse [26]; Schoenbach et al also implemented air/N2 plasma jets by MHCD at 1.5 kV DC voltage [27]; moreover, the temperatures of those jets are close to room temperature, which is suitable for the treatment of heat sensitive materials. Pei et al found that the MHCD jet has better performances in self-pulsing mode than in 'true' DC mode [7]. Duan and Li et al drove the MHCD with a positive pulse and obtained two development processes of the jet during one period of voltage pulse [28, 29]. However, the effect of pulse polarities on MHCD jet has not been well studied.
In this paper, the behavior of the micro-hollow cathode helium jet driven by positive and negative polarity pulses was comparatively presented. This work aims to analyze the influence of positive and negative polarity pulses on the characteristics and propagation mechanism of the MHCD jet.
The experimental setup is shown in figure 1. The discharge device is a typical electrode-dielectric-electrode sandwich structure [28, 29]. The electrodes are made of Mo discs, and the dielectric layer is made of ceramic. Both the two molybdenum discs are 15 mm in diameter and 0.8 mm in thickness. The thickness of the ceramic layer between the two molybdenum discs is also 0.8 mm. The diameter of the ceramic plate is 25 mm to ensure good insulation. A hole with a diameter of 0.5 mm drills through the molybdenum-ceramics-molybdenum structure. The working gas helium flows through this hole, and the discharge is ignited in it. The Mo disc upstream of the gas flow is connected to the output of the positive or negative pulsed power supply and acts as the power electrode. The Mo disc at the downstream of the gas flow is fixed by a large metal ring and then grounded. This apparatus is operated in open air at atmospheric pressure.
The discharge is driven by a positive or negative high-voltage pulsed supply. The output voltage of the supply is a uni-polar square waveform with a rising/falling edge of ~200 ns [30]. The amplitude of the voltage Vamp ranges from 0 to 3 kV. The frequency of the voltage pulse f can be varied from 100 Hz to 20 kHz with adjustable duty ratio dr. The voltage on the power electrode was measured by a high-voltage probe (P6015A, Tektronix). The discharge current passing through the wire connected to the grounded electrode was detected by a current probe (Pearson 2877, Pearson Electronics). With the two probes, the voltage and current waveforms were recorded by a digital oscilloscope (DPO 4034B, Tektronix). High purity helium flow (Beijing AP BAIF Gases Industry Co, Ltd, 99.999%) was controlled by a gas flow-meter (Seven Star CS200) with a flow rate of 0.7 l min-1. The time-integrated and time-resolved images of the MHCD plasma jet are recorded by a digital camera (Canon EOS 550D) and an intensified charge-coupled device (ICCD) camera (Andor iStar DH734) controlled by a computer, respectively. The time-integrated optical spectrum of the plasma jet is detected by a spectrometer (AvaSpec-3648, Avantes) with a spectral range of 200–1100 nm and a wavelength resolution of 0.1 nm. An optical-fiber was placed 1 mm away from the metal ring to guide the light of the jet into the spectrometer. A spectrograph (SR-C500i-CB1, Andor) and an ICCD camera (iStar DH734, Andor) were used to obtain the time-resolved spectrum. A slit was set up along the propagation direction of the plasma jet to collect the light emission of the entire jet into the spectrograph.
The voltage–current waveforms of the MHCD driven by positive and negative polarity pulses are presented in figures 2(a) and (b), respectively. In the experiments of this work, the frequency f of both positive and negative pulses are set to be 2 kHz, and the duty ratio dr = 4.8%. Hence, the pulse width tw is about 12 μs, as shown in figure 2. From the voltage–current waveform of the positive pulse in figure 2(a), it can be found that the applied voltage on the power electrode is about 920 V. There is a 1.6 μs breakdown delay time between the rising edges of the current and the voltage waveforms. During the rising phase, the discharge current increases to ~750 mA, then becomes stable gradually. The voltage on the power electrode drops to ~300 V accordingly. The changes in the current and voltage waveforms are similar to the results of [28, 31], and it is considered that the discharge is operated in a glow-like regime [31].
Similar waveforms of the voltage and current are also observed in the negative pulse discharge of MHCD. For comparison, the stable discharge current of the negative pulse is adjusted to be the same as that of the positive pulse. As shown in figure 2(b), to obtain stable discharge parameters of 300 V/750 mA, the supplied voltage of the negative pulse is adjusted to 800 V roughly. Therefore, the delay time of negative pulse discharge is about ~3 μs, which is longer than that of positive pulse discharge.
Figure 2 also presents the corresponding time-integrated images of the plasma jet driven by positive and negative pulses. In all experiments of this work, the flow rate of helium is fixed at 0.7 l min-1. The jet images of the positive and negative pulses are different in figure 2. For convenience, the plasma jet driven by a positive polarity pulse is denoted as 'positive pulse jet' in the following part, and the jet of negative polarity pulse as 'negative pulse jet'. From the results in figure 2, one can find that the time-integrated image of a positive pulse jet includes a long weak light emission region and a short strong emission region, while the image of the negative pulse jet has only a short strong light radiation region. The total length of the positive pulse jet is about twice that of the negative pulse jet.
Figures 3 and 4 present the time-resolved images of the positive pulse jet and negative pulse jet, respectively. Each image is accumulated in ten discharge pulses by ICCD camera with 50 ns gate width. The gate of ICCD camera is triggered by the rising edge of the positive voltage pulse and the falling edge of the negative voltage pulse. The acquisition time of each image is marked separately with '★' on the current waveforms in figures 2(a) and (b), and the time intervals between the first and the last images in figures 3 and 4 cover the whole current pulse widths in figures 2(a) and (b) correspondingly.
The results show that the propagation processes of the plasma jets driven by positive and negative pulses are quite different. From figure 3, it can be found clearly that the evolution of the positive pulse jet includes two stages. The first stage is from 1.6 to 2.5 μs, which corresponds to the phase of the current rising rapidly. The second stage is from 7 to 12 μs during which the current is almost constant. The image of 1.66 μs shows that the jet of the first stage is formed outside of the cathode hole with a fairly weak light emission region. At 1.71 μs, the light emission region expands towards the downstream of the gas flow, and the light intensity becomes much stronger. After that, although the light emission region develops forward further (see the images of 1.93 μs and 2.55 μs), the intensity of light emission becomes weaker gradually. Until 7.17 μs, no distinct light emission is observed by ICCD outside the cathode hole. It means that although the discharge continues and the current increases to a stable value, the plasma jet of the first stage fades away. After 8.66 μs, a strong light emission region emerges again, which corresponds to a new stage of the plasma jet. According to the image at 11.54 μs in figure 3, the second stage jet continues until the end of the voltage pulse.
However, driven by the negative pulse, only one stage of the plasma jet is observed, as shown in figure 4. Although the discharge has been ignited and developed rapidly, the light emission outside the cathode can not be detected by ICCD during the phase of rapid increase of the current (see the images from 3.05 to 4.2 μs in figure 4). At 8.14 μs, weak light emission can be detected at the outside of the cathode hole. A strong light emission region appears on the image of 9.35 μs in figure 4, and the luminous region moves forward slightly in the next 2 μs. These results indicate that the plasma jet of the negative pulse is formed during the stable current phase, which is the same as that of the second stage jet of positive pulse.
According to the time-resolved images, the propagation velocities of the plasma jets in the two different pulse were estimated respectively. The time-resolved images were recorded with time-step of 50 ns. The propagation velocity of the plasma jets at a given time was estimated by the axial position of the light emission front in two continuous images. Figure 5 provides the curves of the jet speed of positive pulse in the two stages, respectively. Initially, the jet speed of the positive pulse in the first stage is about 10 000 m s-1, as shown in figure 5(a). Then the speed slows down gradually and finally reaches about 1500 m s-1 at 3.5 μs. The curve in figure 5(b) indicates that the speed of the positive pulse jet in the second stage is only a few hundred m s-1, which is about one order lower than that of the first stage jet. The different speeds of the plasma jet in the two stages correspond to different mechanisms of jet propagation. In the first stage, the jet speed of 103–104 m s-1 is similar to that of DBD jet or needle-ring jet. This high-speed jet is considered to be the propagation of ionization wave of positive corona and mainly driven by the space electric field [32]. In the second stage of the plasma jet, the jet speed of several hundred m s-1 is 1–2 orders lower than that observed in ionization wave propagation. Low-speed jet is considered to be related to gas flow. Figure 6 presents the development speed of the negative pulse jet as a function of time. The jet speed of the negative pulse is also several hundred m s-1, which is similar to that of the positive pulse jet in the second stage.
These results indicate that there are two different mechanisms involved in the propagation of the MHCD jet. Under the positive voltage pulse, before the discharge, the main component of the electric field is along the direction of air flow. At the rising edge of the current, the plasma contracts towards the grounded electrode, which enhances the electric field and causes the propagation of jet. With the negative pulse, the direction of the electric field is opposite to the gas flow. Therefore, during the falling edge of the negative current pulse, no jet was observed downstream of the gas flow, which confirms that the electric field drives the propagation of the first stage jet of the positive pulse.
The gas thermal expansion effect is considered to be an important factor for the jets of the stable current phase [28]. After the breakdown, the input power begins to heat the gas. Then the plasma expands out of the grounded electrode to form the jet. The propagation of these jets depends on the gas expansion velocity rather than the electric field. Therefore, the jets of the stable current phase can be observed under both positive and negative polarity pulses, and these jets propagate at similar speeds and distances.
The species of nitrogen and oxygen play an important role in the applications of plasma interaction with biological objects. Optical emission spectroscopy of the positive and negative plasma jets was diagnosed to obtain the information of excited species. Due to the helium jet operated in open air, a small amount of air will be mixed into helium in the path of jet propagation. The discharge will excite the nitrogen and oxygen molecules/atoms. Therefore, the spectral lines of helium, nitrogen and oxygen will be observed, which are similar to the results of He/air discharge [21, 33]. The time-integrated optical spectra of the positive and negative plasma jets are shown in figure 7. The spectra of both polarity plasma jets are very similar, mainly including the emissions of He (587.5 nm, 667.8 nm, and 706.5 nm), He+ (656.1 nm), N2+ (391.4 nm), and O (777.4 nm). The most intensive emission line is 587.5 nm of He excited atom. It can be found that the relative intensities of N2+ (391.4 nm) and O (777.4 nm) of the positive pulse jet are slightly higher than those of the negative pulse jet, which indicates higher number of densities of these excited species in the positive plasma jet.
In order to investigate the characteristics of excited species of nitrogen and oxygen under different polarity pulses, the time-resolved emission spectra of N2+ (391.4 nm) and O (777.4 nm) were recorded by an ICCD camera combined with a spectrometer. In the acquisition of the time-resolved spectrum, the emissions along the whole jet were collected. These emission lines of 391.4 nm and 777.4 nm in the helium APPJs are associated with the following transitions:
| N+2(B2+∑u,ν)→N+2(X2+∑g,ν)+hv(391.4nm) | (1) |
| O(35P)→O(35S)+hv(777.4nm). | (2) |
Figures 8 and 9 present the evolution of the emission intensity of 391.4 nm and 777.4 nm under the two polarity pulses, respectively. From figure 8(a), it can be seen that at the rising edge of the positive current pulse, the emission of N2+ appears immediately. The intensity of 391.4 nm reaches the peak at 3 μs, then decreases gradually. At about 8 μs, a new intensity peak of 391.4 nm appears. In the negative polarity jet, the emission of 391.4 nm is detected after 6 μs, and only one intensity peak appears around 9 μs, as shown in figure 8(b). The transient evolutions of N2+ emission in figures 8(a) and (b) correspond with respective propagations of positive and negative pulse jets.
In figure 9(a), the intensity peak of O emission (777.4 nm) of the positive pulse jet appears after 4 μs. The direct electron-molecular dissociation collision (ϵexc = 15.78 eV) between the energetic electrons and the ground state O2 can generate the excited atoms of O. There is a time lag between the peak of 777.4 nm and the rising edge of the positive current pulse. It means that the excited state of O is not mainly generated by the direct dissociation collision. The following Penning reaction between the metastable state Hem and O2 will be more important for the generation of O(35P).
| Hem+O2→He+O(35P)+O. | (3) |
From figure 9(a), one can find that after the peak at 4 μs, the intensity of 777.4 nm decreases gradually. That is, only one peak of 777.4 nm of the positive pulse jet is observed, which is different from the two peaks of 391.4 nm in figure 8(a). In figure 9(b), the intensity of 777.4 nm is about half of that in figure 9(a). It means that the generation of excited atom O during the stable current phase is much less than that during the rising edge of the positive current pulse. After the rising edge of the positive current pulse, the excited atom O can be generated by the reaction (3) continually due to the long lifetime of Hem. The decrease of excited atom O is mainly caused by the combination with O2 to form O3. This process is relatively slow. Therefore, the emission intensity of 777.4 nm maintains a high value after the rising edge of the current pulse. The emission intensity of O is related to the electron density, species density and electron temperature, as IO ∝ nOne〈σv〉, where nO is the species density, ne the electron density, and 〈σv〉 is the integration of the electron energy distribution function with the relevant excitation cross section. The emission intensity has positive correlation with the density of O atom. These results show that the first stage of the positive pluse jet can generate specie O more efficiently.
In this work, the characteristics and the time-resolved emission spectra of micro-hollow cathode plasma jets driven by positive and negative polarity pulses are investigated. The ICCD images show that the propagation of the positive pulse jet can be divided into two stages. The plasma jet of the first stage is generated at the rising edge of the pulse current, and the second stage jet is generated when the current becomes stable. The propagation of the negative pulse jet is only observed during the current stable phase. The propagation speeds and distances of the jets in the two phases are obviously different. These results confirm that the propagation of the positive pulse jet during the rising edge is mainly caused by the electric field, while the jets during the current stable phase are mainly caused by the thermal gas expansion. The time-resolved spectra of N2+ and O emissions are also presented. It is found that the evolution of emission intensity of N2+ of the positive pulse jet has two peaks, while the intensity of O of the positive pulse jet has only one peak. The generation of specie O in the jet driven by the electric field is more efficient. Besides, the Penning effect induced by the metastable state Hem with O2 plays a crucial role in the dynamics of the plasma jet in the open air. Summarily, this work can provide a deep insight of the plasma jet excitation and propagation in micro hollow cathode structure by different polarity pulses, and is helpful to tune reactive species population in the plasma jet.
This work was supported by National Natural Science Foundation of China (No. 11975047).
| [1] |
Lu X et al 2016 Phys. Rep. 630 1 doi: 10.1016/j.physrep.2016.03.003
|
| [2] |
Penkov O V et al 2015 J. Coat. Technol. Res. 12 225 doi: 10.1007/s11998-014-9638-z
|
| [3] |
Norberg S A et al 2014 J. Phys. D: Appl. Phys. 47 475203 doi: 10.1088/0022-3727/47/47/475203
|
| [4] |
Viegas P et al 2022 Plasma Sources Sci. Technol. 31 053001 doi: 10.1088/1361-6595/ac61a9
|
| [5] |
Jin S H et al 2022 Front. Phys. 10 928402 doi: 10.3389/fphy.2022.928402
|
| [6] |
Heneral A A and Avtaeva S V 2020 J. Phys. D: Appl. Phys. 53 195201 doi: 10.1088/1361-6463/ab7354
|
| [7] |
Pei X K et al 2018 J. Phys. D: Appl. Phys. 51 384001 doi: 10.1088/1361-6463/aad4e9
|
| [8] |
Remigy A et al 2022 Phys. Plasmas 29 113508 doi: 10.1063/5.0110318
|
| [9] |
Teschke M et al 2005 IEEE. Trans. Plasma Sci. 33 310 doi: 10.1109/TPS.2005.845377
|
| [10] |
Lu X P and Laroussi M 2006 J. Appl. Phys. 100 063302 doi: 10.1063/1.2349475
|
| [11] |
Mericam-Bourdet N et al 2009 J. Phys. D: Appl. Phys. 42 055207 doi: 10.1088/0022-3727/42/5/055207
|
| [12] |
Shao T et al 2014 Europhys. Lett. 107 65004 doi: 10.1209/0295-5075/107/65004
|
| [13] |
Shi J J et al 2008 Phys. Plasmas 15 013504 doi: 10.1063/1.2828551
|
| [14] |
Chen Z Q et al 2020 Plasma Sci. Technol. 22 085403 doi: 10.1088/2058-6272/ab8d1b
|
| [15] |
Lietz A M et al 2020 J. Appl. Phys. 128 083301 doi: 10.1063/5.0020264
|
| [16] |
Jiang C et al 2009 J. Phys. D: Appl. Phys. 42 232002 doi: 10.1088/0022-3727/42/23/232002
|
| [17] |
Wang R X et al 2015 J. Appl. Phys. 118 123303 doi: 10.1063/1.4931668
|
| [18] |
Qian M Y et al 2017 Plasma Sci. Technol. 19 064015 doi: 10.1088/2058-6272/aa6154
|
| [19] |
Joh H M et al 2019 Phys. Plasmas 26 053509 doi: 10.1063/1.5090556
|
| [20] |
Xiong Z et al 2010 J. Appl. Phys. 108 103303 doi: 10.1063/1.3511448
|
| [21] |
Wang R X et al 2016 Plasma Sources Sci. Technol. 25 015020 doi: 10.1088/0963-0252/25/1/015020
|
| [22] |
Jiang Y Y et al 2021 J. Appl. Phys. 130 233301 doi: 10.1063/5.0070830
|
| [23] |
Liu Z J et al 2018 Plasma Chem. Plasma Process. 38 953 doi: 10.1007/s11090-018-9920-4
|
| [24] |
Schoenbach K H et al 1997 Plasma Sources Sci. Technol. 6 468 doi: 10.1088/0963-0252/6/4/003
|
| [25] |
He S J et al 2018 Plasma Sci. Technol. 20 054006 doi: 10.1088/2058-6272/aab54b
|
| [26] |
Hong Y C and Uhm H S 2007 Phys. Plasmas. 14 053503 doi: 10.1063/1.2736945
|
| [27] |
Mohamed A A H et al 2010 Eur. Phys. J. D 60 517 doi: 10.1140/epjd/e2010-00220-7
|
| [28] |
Duan Z C et al 2021 Plasma Sources Sci. Technol. 25 025001 doi: 10.1088/1361-6595/abdaa2
|
| [29] |
Li P Z et al 2021 Plasma Sci. Technol. 23 085401 doi: 10.1088/2058-6272/ac0719
|
| [30] |
Duan Z C et al 2018 J. Phys. D: Appl. Phys. 51 065201 doi: 10.1088/1361-6463/aaa31a
|
| [31] |
Wei H C et al 2018 Phys. Plasmas 25 123513 doi: 10.1063/1.5063450
|
| [32] |
Zhu P et al 2018 Phys. D: Appl. Phys. 51 405202 doi: 10.1088/1361-6463/aadb12
|
| [33] |
Nersisyan G and Graham W G 2004 Plasma Source Sci. Technol. 13 582 doi: 10.1088/0963-0252/13/4/005
|
| [1] | Qiuyun WANG (王秋云), Anmin CHEN (陈安民), Wanpeng XU (徐万鹏), Dan ZHANG (张丹), Ying WANG (王莹), Suyu LI (李苏宇), Yuanfei JIANG (姜远飞), Mingxing JIN (金明星). Time-resolved spectroscopy of femtosecond laser-induced Cu plasma with spark discharge[J]. Plasma Science and Technology, 2019, 21(6): 65504-065504. DOI: 10.1088/2058-6272/ab0fa6 |
| [2] | Manjeet SINGH, Arnab SARKAR. Time-resolved evaluation of uranium plasma in different atmospheres by laser-induced breakdown spectroscopy[J]. Plasma Science and Technology, 2018, 20(12): 125501. DOI: 10.1088/2058-6272/aad866 |
| [3] | Guanlei DENG (邓官垒), Qikang JIN (金杞糠), Shengyong YIN (殷胜勇), Chao ZHENG (郑超), Zhen LIU (刘振), Keping YAN (闫克平). Experimental study on bacteria disinfection using a pulsed cold plasma jet with helium/ oxygen mixed gas[J]. Plasma Science and Technology, 2018, 20(11): 115503. DOI: 10.1088/2058-6272/aacaee |
| [4] | Zilu ZHAO (赵紫璐), Dezheng YANG (杨德正), Wenchun WANG (王文春), Hao YUAN (袁皓), Li ZHANG (张丽), Sen WANG (王森). Volume added surface barrier discharge plasma excited by bipolar nanosecond pulse power in atmospheric air: optical emission spectra influenced by gap distance[J]. Plasma Science and Technology, 2018, 20(11): 115403. DOI: 10.1088/2058-6272/aac881 |
| [5] | Shoujie HE (何寿杰), Peng WANG (王鹏), Jing HA (哈静), Baoming ZHANG (张宝铭), Zhao ZHANG (张钊), Qing LI (李庆). Effects of discharge parameters on the micro-hollow cathode sustained glow discharge[J]. Plasma Science and Technology, 2018, 20(5): 54006-054006. DOI: 10.1088/2058-6272/aab54b |
| [6] | Mingming SUN (孙明明), Tianping ZHANG (张天平), Xiaodong WEN (温晓东), Weilong GUO (郭伟龙), Jiayao SONG (宋嘉尧). Plasma characteristics in the discharge region of a 20A emission current hollow cathode[J]. Plasma Science and Technology, 2018, 20(2): 25503-025503. DOI: 10.1088/2058-6272/aa8edb |
| [7] | Xingwei WU (吴兴伟), Cong LI (李聪), Chunlei FENG (冯春雷), Qi WANG (王奇), Hongbin DING (丁洪斌). Time-resolved measurements of NO2 concentration in pulsed discharges by high-sensitivity cavity ring-down spectroscopy[J]. Plasma Science and Technology, 2017, 19(5): 55506-055506. DOI: 10.1088/2058-6272/aa6473 |
| [8] | LAN Hui (兰慧), WANG Xinbing (王新兵), ZUO Duluo (左都罗). Time-Resolved Optical Emission Spectroscopy Diagnosis of CO2 Laser-Produced SnO2 Plasma[J]. Plasma Science and Technology, 2016, 18(9): 902-906. DOI: 10.1088/1009-0630/18/9/05 |
| [9] | M. L. SHAH, A. K. PULHANI, B. M. SURI, G. P. GUPTA. Time-Resolved Emission Spectroscopic Study of Laser-Induced Steel Plasmas[J]. Plasma Science and Technology, 2013, 15(6): 546-551. DOI: 10.1088/1009-0630/15/6/11 |
| [10] | HE Feng (何锋), HE Shoujie (何寿杰), ZHAO Xiaofei (赵晓菲), GUO Bingang (郭滨刚), OUYANG Jiting (欧阳吉庭). Study of the Discharge Mode in Micro-Hollow Cathode[J]. Plasma Science and Technology, 2012, 14(12): 1079-1083. DOI: 10.1088/1009-0630/14/12/08 |
Supported by: Beijing Renhe Information Technology Co., Ltd. 
DownLoad:
