Accepts
Note: The papers published below will continue to be available from this page until they are assigned to an issue. To see an article, click its [PDF] link. To review many abstracts, check the boxes to the left of the titles you want, and click the 'Selected articles' button. To see one abstract at a time, click its [Abstract] link.
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Characteristics of Long Gap AC Streamer Discharges Under Low Pressure Condition

Yaqi YANG (杨亚奇)*, Weiguo LI (李卫国), Yu XIA (夏喻), Chuangye YUAN(袁创业)
Accept: 2017-06-15
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The generation and propagation of streamer is a significant physical process of air gap discharge. Research on the mechanism of streamer under low pressure condition is helpful for understanding the process of long gap discharge at high altitude area. This paper describes laboratory investigations of streamer discharge under alternating current (AC) voltage in low pressure test platform for 60 cm rod–plane gap at 30 kPa, and analyze the characteristics of streamer generation and propagation. The results show that the partial streamer and breakdown streamer all occur in positive half–cycle of AC voltage near the peak voltage at 30 kPa. The partial streamer could cause distortion of current and voltage waveform, and it appears branching characteristic at the initial stage. With the extension of streamer, the branching and tortuosity phenomena gradually obvious, but the branching are suppressed when streamer crosses the gap. Low pressure condition has little influence on the tortuosity length and the number of tortuosity of streamer, but effect the diameter of streamer obviously.
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Hybrid-PIC simulation of sputtering products distribution in a Hall thruster

Xifeng CAO (曹希峰)1), Guanrong HANG (杭观荣)2), Hui LIU (刘辉) 1,a), Yingchao MENG (孟颖超) 1), Xiaoming LUO (罗晓明) 1), Daren YU (于达仁) 1)
Accept: 2017-06-13
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Hall thruster have been used widely in orbit correction and station-keeping of geostationary satellites for the advantage of high specific impulse, long life, and high reliability. During the operating life of a Hall thruster, high-energy ions will bombard the discharge channel and cause serious erosion. With the time passing by, this sputtering process will change the macroscopic surface morphology of the discharge channel, especially near the exit, thus affect the performance of the thruster. Therefore, it is necessary to carry out research on the motion of the sputtering products and erosion process of the discharge wall. To better understand the moving characteristics of sputtering products, based on hybrid particle-in-cell (PIC) numerical method, this paper simulates the different erosion states of the thruster discharge channel in different moments and analyzes the moving process of different particles, such as B atoms and B+ ions. In this paper, the main conclusion is that the B atoms are mainly produced on both sides of the channel exit, and the B+ ions is mainly produced in the middle of the channel exit. The ionization rate of B atoms is approximately 1%.
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Environmental and EconomicalVision ofPlasmaTreatment of Waste in Makkah

Ahmed Rida Galaly1, 2,*, Guido Van Oost3, 4
Accept: 2017-06-07
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An environmental and economicassessment of the development of a plasma-chemical reactor equipped with plasma torches for the environmentally friendly treatment of waste streams by plasmais outlinedwith a view to the chemicaland energetic valorization of the sustainabilityin the Kingdom Saudi Arabia (K.S.A),especially in the pilgrimage season in the city of Makkah, which is a major challenge since the amount of wasteisestimated at about 750 thousand tons through Arabic Year 1435 H (2015), andis growing at a rate of 3-5 percent annually.According to statistics, the value of waste in Saudi Arabia ranges between 8 and9billion EUR. The Plasma Treatment Project(PTP) of direct plasma treatment of all types of waste (from source and landfill), as well as an environmental vision and economic evaluation of the use of the gas produced for fuel and electricity production in the Kingdom of Saudi Arabia, especially in the pilgrimage season in the holy city Makkah. The electrical power required for the plasma treatment process is estimated at 5,000 kW(2000 kW used for the operation of the system and 3000 kW sold),taking into account the facts that:- (1) the processing capacity of solid waste is 100 tonsper day (2) the sale of electricity amounts to 23.8 MW at 0.18 EUR per kWh. (3) The profit from the sale of electricity per year is estimatedat 3.27 million EURand the estimated profits of solid waste treatment amounts to 6 million EUR per year and (4) the gross profit per ton of solid waste totaling 8 million EUR per year. The present article introduces the first stage of the PTP in Makkah in thepilgrimageseasons, which consists of five stages: - (1) study and treatment of waste streams, (2) slaughterhouse (SGH) waste treatment, (3) treatment of refuse derived fuel (RDF), (4) treatment of car tires; (5) treatment of slag (the fifth stage associated with each stage from the four previous stages)
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Experiment and analysis on the neutralization of the electron cyclotron resonance ion thruster

Yizhou JIN (金逸舟)1, Juan YANG (杨涓)1,a), Jun SUN (孙俊)2,3, Xianchuang LIU (刘宪闯)1, Yizhi HUANG (黄益智)1
Accept: 2017-06-02
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 An electron cyclotron resonance (ECR) ion thruster must emit the electron current equivalent to its ion beam current to prevent the thruster system being electrically charged. This operation is defined as neutralization. The factors, which influence the neutralization, are categorized into the ion beam current, neutralizer input parameters, and the neutralizer positions. For understanding the mechanism of the neutralization, the experiment and calculation study about how these factors influence the thruster neutralization are presented. The experiment results showed that the minimum bias voltage of the neutralizer was -60 V at ion beam current in 80 mA for argon propellant, and a critical gas flow rate existed, below which the coupling voltage increased sharply. Based on the experiment, the neutralization is analyzed by means of a one-dimensional calculation model. The computing results show that, the coupling voltage are influenced by the beam divergence and the negative potential zone near the grids.

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Some studies on transient behaviours of sheath formation in dusty plasma with the effect of adiabatic heated electrons and ions

G. C. Das
Accept: 2017-05-25
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Based on quasipotential analysis, plasma sheath has been studied through the derivation of Sagdeev potential equation in dusty plasma coexisting with adiabatically heated electrons and ions. Salient features on the existences of sheath have shown by solving Sagdeev potential equation by Runge-Kutta method that too with appropriate consideration of adiabatically heated electrons and ions in the dynamical system.  It has shown that adiabatic heating of plasma sets a limit to the critical dust speed depending on the densities and Mach number and believe the  role is very important on  sheath.  Present problem finds  the contraction  of sheath region due to which  levitated dust grains into sheath leads a  crystallization as similar to  the formation of nebulons,  and are  to be compressed  to a larger chunk of dust cloud by the shrinking of sheath. Overall observations could be an advanced knowledge on sheath formation causeway study expects to be of interest in astroplasmas.

 

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Specifications of Nanosecond-Laser Ablation with Solid Targets, Aluminum, Silicon-Rubber and Polymethylmethacrylate (PMMA)

Nader MORSHEDIAN
Accept: 2017-05-23
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The ablation parameters such as threshold fluence, etch-depth, ablation-rate and the effect of material targets were investigated under the interaction of laser pulse with low intensity. The parameters of laser system are as: laser pulse energy in the range of, 110-140  mJ, wavelength, 1064 nm and pulse duration, 20 ns. By macroscopic estimation of outward images of ablation and data obtained, we can conclude that the photothermal and photoionization processes have more influences for Aluminum ablation. In contrast, for Polymer samples, the macroscopic observation of the boarder pattern at the irradiated spot, and also the data obtained from the experiment results, we deduce that the both chemical change due to heating and photochemical dissociation were effective mechanisms of ablation. However concerning the two polymer samples, apart from considering the same theoretical ablation model, it is conceived that the photomehanical specifications of PMMA are involved in the ablation parameters. The threshold flunce for ablation rate of 30 laser shot, were obtained, 12.4 Jcm-2, 24.64 Jcm-2 and 11.71 Jcm-2, for Aluminum, Silicon-Rubber and PMMA respectively. The ablation rate is exponentially decreased by laser-shot number especially for Aluminum. Furthermore, the etch depth after 30 laser shot was measured 180 μm, 630 μm and 870 μm, for Aluminum, Silicon-Rubber and PMMA respectively.

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The effect of substrate holder size on the electric field and discharge plasma on diamond-film formation at high deposition rates during MPCVD

Kang AN (安康), Liangxian CHEN (陈良贤), Jinlong LIU (刘金龙), Yun ZHAO (赵云), Xiongbo YAN (闫雄伯), Chenyi HUA (化称意), Jianchao GUO (郭建超), Junjun WEI (魏俊俊), Lifu HEI (黑立富), Chengming LI (李成明),Fanxiu Lu (吕反修)
Accept: 2017-05-19
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The effect of the substrate holder feature dimensions on plasma density (ne), power density (Qmw) and gas temperature (T) of a discharge marginal plasma (a plasma caused by marginal discharge) and homogeneous plasma were investigated for the microwave plasma chemical vapor deposition (MPCVD) process. Our simulations show that decreasing the dimensions of substrate holder in radical direction and increasing the dimension of it in the direction of the axis helps to produce the marginally inhomogeneous plasma. When the marginal discharge appears, the maximum plasma density and power density appear at the edge of the substrate. The gas temperature increases until a marginally inhomogeneous plasma develops. The marginal inhomogeneous plasma can be avoided using a movable substrate holder that can tune the plasma density, power density, and gas temperature. It also can ensure the power density and electron density as high as possible with uniform distribution of plasma. Moreover, both inhomogeneous and homogeneous diamond films were prepared using a new substrate holder with a diameter of 30 mm. The observation of inhomogeneous diamond films indicates that the marginal discharge can limit the deposition rate in the central part of the diamond film. The successfully produced homogeneous diamond films show that by using a substrate holder it is possible to deposit diamond film at 7.2 μm/h at 2.5 kW microwave power.

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Development of a dimensionless parameter for characterization of dielectric barrier discharge devices with respect to geometrical features

LIM Mook Tzeng (林木森)*, Ahmad Zulazlan SHAH ZULKIFLI, Kanesh Kumar JAYAPALAN, CHIN Oihoong
Accept: 2017-05-16
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Non-thermal plasma (NTP) devices produce excited and radical species that have higher energy levels than their ground state and are utilized for various applications. There are various types of NTP devices, with dielectric barrier discharge (DBD) reactors being widely used. These DBD devices are varied in geometrical configuration and operating parameters, making a comparison of their performance in terms of discharge power characteristics difficult. Therefore, this study proposes a dimensionless parameter that is related to the geometrical features, and is a function of the discharge power with respect to the frequency, voltage, and capacitance of a DBD. The dimensionless parameter, in the form of a ratio of the discharge energy per cycle to the gap capacitive energy, will be useful for engineers and designers to compare the devices’ energy characteristics systematically, and could also be used for scaling up DBD devices. From the results in this experiment and from literature, different DBD devices were able to be categorized into three separate groups according to different levels of the energy ratio. The larger DBD devices have lower energy ratios due to their lower estimated surface discharge areas and capacitive reactance. Therefore the devices can be categorized according to the energy ratio due to the effects of geometrical features of the DBD devices, since it affects the surface discharge area and capacitance of the DBD. The DBD devices were also categorized into three separate groups using the Kriegseis factor, but the categorization was different from that of the energy ratio.

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Discharge Electrode Configuration Effects on the Performance of a Plasma Sparker

Yanliang PEI (裴彦良) 1,2, Liancheng ZHANG (张连成) 3, Yifan HUANG (黄逸凡) 3, Hui YAN (严辉) 3, Xinlei ZHU (朱鑫磊) 3, Zhen LIU (刘振) 3, Keping YAN (闫克平) 3
Accept: 2017-05-11
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  A multi-electrode array is commonly applied in a plasma sparker to generate stable acoustic pulses. In this paper, the effects of the electrode configuration on the performance of a plasma sparker have been investigated. In terms of the load electrical characteristics, the electrode radius and distance have negligible influence on the electric characteristics, whereas a larger electrode number results in a smaller voltage and a larger current but has little effect on the load energy. Regarding the acoustic characteristics, both the expansion and collapse pulses can be increased by decreasing the electrode tip radius. the influence of the electrode number and electrode gap distance on the amplitude of the expansion pulse was found to be negligible. And the amplitude of the collapse pulse decreases significantly with increasing electrode number. Increasing the electrode number decreases the energy efficiency for intense bubble interactions, thus, a small electrode tip radius and a small electrode number are preferred for the design of a plasma sparker if the total discharge energy is given.

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Investigation of nanosecond-pulsed dielectric barrier discharge cctuators with powered electrode of different exposures

Shuangyan XU (徐双艳) 1, Jinsheng CAI (蔡晋生) 1, Yongsheng LIAN (练永生) 2
Accept: 2017-04-24
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Nanosecond-pulsed dielectric barrier discharge actuators with powered electrodes of different exposures were investigated numerically by using a newly proposed plasma kinetic model. The governing equations include the coupled continuity plasma discharge equation, the drift-diffusion equation, electron energy equation, Poisson’s equation, and the Navier-Stokes equations. Powered electrodes of three different exposures were simulated to understand the effect of surface exposure on plasma discharge and surrounding flow field. Our study showed that the fully exposed powered electrode resulted in earlier reduced electric field breakdown and more intensive discharge characteristics than partially exposed and rounded-exposed ones. Our study also showed that the reduced electric field and heat release concentrated near the right upper tip of the powered electrode. The fully exposed electrode also led to stronger shock wave, higher heating temperature, and larger heated area.
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Preliminary study of divertor particle exhaust in the EAST superconducting tokamak

Huan LIU (刘欢)1,2, Liang WANG (王亮)1,*, Guosheng XU (徐国盛)1, et al,
Accept: 2017-04-24
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The particle exhaust of upper tungsten and lower carbon divertors in EAST has been preliminarily studied during the 2016 experimental campaign. The density decay time during terminating gas puffing has been employed as a key parameter to evaluate the divertor particle exhaust performance. Comparative plasma discharges have been carried out on the particle exhaust performance between two toroidal field directions in upper single null and lower single null divertor configurations. This work has enhanced the understanding of the effects of the in-out asymmetry and divertor geometry on the efficiency of the divertor particle exhaust. In addition, the sensitivity of the particle exhaust capability on different strike point locations has been analyzed. The experimental results are expected to provide important information on the future upgrade of EAST bottom divertor and facilitate the realization of longer pulse operation.
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Study on atomic layer etching of Si in inductively coupled Ar/Cl2 plasmas driven by tailored bias waveforms

Xiaoqin MA(麻晓琴), Saiqian ZHANG(张赛谦), Zhongling DAI(戴忠玲), Younian WANG(王友年)
Accept: 2017-04-13
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Plasma atomic layer etching (PALE) is proposed to attain the layer-by-layer etching, as it has the atomic-scale resolution, can etch monolayer of materials. In the etching process, ion energy and angular distributions(IEADs) bombarding on the wafer placed on substrate play a critical role in trench profile evolution, thus controlling IEADs flexibly in the process is very important. Tailored bias voltage waveform is an advisable method to modulate the IEADs effectively, and then improve the trench profile. In this paper, a multiscale model, coupling the reaction chamber model, sheath model and trench model, is used to research the effects of bias waveforms on the atomic layer etching of Si in Ar/Cl2 inductively coupled plasmas. Results show that different discharge parameters, such as pressure and radio-frequency power influence the trench evolution progress with bias waveforms synergistically. Tailored bias waveforms can provide nearly monoenergetic ions, thereby obtain more anisotropic trench profile.
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Analysis of the primary experimental results on a 5 cm diameter ECR Ion Thruster

Yujun KE (柯于俊), Xinfeng SUN* (孙新锋), Xuekang CHEN (陈学康), Licheng TIAN (田立成), Tianping ZHANG (张天平), Maofan ZHENG (郑茂繁), Yanhui JIA (贾艳辉), Haocheng JIANG (江豪成)
Accept: 2017-04-13
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An ECR Ion Thruster with a diameter of 5 cm has been developed and tested. Four different antenna positions are experimentally and numerically investigated, which suggests that the optimal location for the antenna is where it is perfectly surrounded by the electron cyclotron resonance layer. We also evaluated two different antenna configurations, and found that the star configuration is preferable to the circular configuration, and the efficiency of the circular antenna is only 40% of the star antenna. The experimental curve of ion beam current and voltage agrees with the fitting results from the analytic solution. The simulation of magnetic topology in discharging chamber with different back yoke heights indicates that it needs to be further verified.
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On peak current in atmospheric pulse-modulated microwave discharges by PIC-MCC model

Yuantao ZHANG (张远涛), Yu LIU (刘雨), and Bing LIU (刘冰)
Accept: 2017-03-29
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Pulse modulation provides a new way to tailor the electron density, electron energy and gas temperature in atmospheric radio-frequency (rf) discharges. In this paper, by increasing the rf frequency to several hundreds of MHz, or even much higher to the range of GHz, a very strong Peak Current in the First Period (PCFP) with much larger electron energy can be formed during the power-on phase, which is not observed in the common pulse modulation discharges at a rf frequency of 13.56 MHz. The PIC-MCC model is explored to unveil the generation mechanism of PCFP, and based on the simulation data a larger voltage increasing rate over a quarter of period and the distribution of electron density just before the power-on phase are believed to play key roles; the PCFP is usually produced in the microplasma regime driven by the pulsed power supply. The effects of duty cycle and pulse modulation frequency on the evolution of PCFP are also discussed from the computational data. Therefore, the duty cycle and pulse modulation frequency can be used to optimize the generation of PCFP and the high-energy electrons.
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One-dimensional ordinary - slow extraordinary - Bernstein mode conversion in the electron cyclotron range of frequencies

Xingyu GUO (郭星宇)1, Zhe GAO (高喆)1* and Guozhang JIA (贾国章)2
Accept: 2017-03-24
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The ordinary - slow extraordinary - Bernstein (O-SX-B) mode conversion in the electron cyclotron range of frequencies (ECRF) is revisited in slab geometry. The analytical formula of the O-SX conversion efficiency by Mj?lhus is upgraded to include the magnetic field gradient, and the analytical expression of the SX-B conversion efficiency by Ram and Schultz is generalized for the case of oblique injection. Therefore, the conversion efficiency and optimal parallel refractive index for the whole O-SX-B conversion are obtained analytically and a shift of optimal parallel refractive index due to SX-FX loss is found. Full wave calculations are also presented to be compared with the analytical results.
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Electrical and Optical Measurements in the Early Hydrogen Discharge of GLAST-III

S. HUSSAIN1, A. QAYYUM1, Z.AHMAD1, S. AHMAD1, R. KHAN1, M. A. NAVEED1, RAFAQAT Ali1, FARAH Deeba1, G. M. VOROBYOV2 and GLAST Team
Accept: 2017-03-21
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This work presents the first electrical and optical measurements of the initial phase of hydrogen discharge in the upgraded spherical tokamak GLAST-III, started with electron cyclotron heating (ECH). Diagnostic measurements provide insights into expected and unexpected physics issues related to initial phase of discharge. A triple Langmuir probe (TLP) has been developed to measure time series of floating potential, plasma electron temperature and number density over entire discharge allowing monitoring the two phases of the discharge: the ECH pre ionization phase following by the plasma current formation phase. TLP has the ability to give time-resolved measurements of floating potential (Vfloat), electron temperature (Te), and ion saturation current (Isat? ne√kTe). The evolution of ECH-assisted pre-ionization and subsequent plasma current phases in one shot are well envisioned by probe. Intense fluctuations in the plasma current phase advocate for efficient equilibrium and feedback control systems. Moreover, emergence of some strong impurity lines in the emission spectrum, even after few shots propose crucial need for improvement in the base vacuum level. A noticeable change in the shape of temporal profiles of floating potential, electron temperature, ion saturation current (Isat) and light emission has been observed with changing hydrogen fill pressure and vertical magnetic field.
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Saw tooth plasma actuator for film cooling efficiency enhancement of shaped hole

Guozhan LI (李国占), Jianyang YU (俞建阳), Huaping LIU (刘华坪), Fu CHEN (陈浮), Yanping SONG (宋彦萍)
Accept: 2017-03-15
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This paper reports the large eddy simulations of the effects of saw-tooth plasma actuator and the laidback fan-shaped hole on the film cooling flow characteristics, and the numerical results are compared with a corresponding standard configuration (cylindrical hole without the saw-tooth plasma actuator). For this numerical research, the saw-tooth plasma actuator is installed just downstream of the cooling hole and a phenomenological plasma model is employed to provide the three-dimensional plasma force vectors. Results show that thanks to the downward force and the momentum injection effect of the saw-tooth plasma actuator, the cold jet becomes closer to the wall surface and extends further downstream. The saw-tooth plasma actuator also induces a new pair of vortex which weakens the strength of counter rotating vortex pair and entrains the coolant towards the wall, and thus the diffusion of the cold jet in the crossflow is suppressed. Furthermore, the laidback fan-shaped hole reduces the vertical jet velocity causing the disappearance of downstream spiral separation node vortices, this compensates for the deficiency of the saw-tooth plasma actuator. Both effects of the laidback fan-shaped hole and the saw-tooth plasma actuator effectively control the development of the counter rotating vortex pair whose size and strength are smaller than those of the anti-counter rotating vortex pair in far field, thus the centerline and the spanwise-averaged film cooling efficiency are enhanced. The average film cooling efficiency is the biggest in the Fan-Dc=1 case, which is 80% bigger than that in the Fan-Dc=0 case and 288% bigger than that in the Cyl-Dc=0 case.
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Investigation of working pressure on the surface roughness controlling technology of glow discharge polymer films based on the plasma diagnosed

Ling ZHANG (张玲), Guo CHEN (陈果), Zhibing HE (何智兵), Xing AI (艾星), Jinglin HUANG (黄景林), Lei LIU (刘磊), Yongjian TANG (唐永建), Xiaoshan HE (何小珊)
Accept: 2017-03-07
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The effects of working pressure on the component, surface morphology, surface roughness, and deposition rate of glow discharge polymer (GDP) films by trans-2-butene/hydrogen gas mixture were investigated based on the plasma characteristics diagnosis. The composition and ion energy distributions of multi-carbon (C4H8/H2) mixture plasma at different working pressures were diagnosed by energy-resolved mass spectrometer (MS) during the GDP films deposition process. The Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (SEM) and white-light interferometer (WLI) results were obtained to investigate the structure, morphology and roughness characterization of the deposited films, respectively. It was found that the degree of ionization of the C4H8/H2 plasma reduces with the working pressure increasing. At low working pressure, the C-H fragments exhibited small-mass and high ion energy in plasma. In this case, the film had low CH3/CH2 ratio, and displayed a smooth surface without any holes, cracks or asperities. While the working pressure increased to 15 Pa, the largest number of large-mass fragments led to the deposition rate reaching a maximum of 2.11 μm/h, and the holes defects on the film surface. However, continuing to increase the working pressure, the film surface became smooth again, and the interface between clusters became unconspicuous without etching pits.
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Control of growth and structure of Ag films by driving frequency of magnetron sputtering

Peifang YANG (杨培芳)1, Chao YE (叶超)1,2, Xiangying WANG (王响英)3, Jiamin GUO (郭佳敏)1, Su ZHANG (张苏)3
Accept: 2017-03-07
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The growth and structural properties of Ag films prepared by radio-frequency (2, 13.56 and 27.12 MHz) and very-high-frequency (40.68 and 60 MHz) magnetron sputtering were investigated. Using 2 MHz sputtering, the Ag film has a high deposition rate, an uniform and smooth surface, and a better fcc structure. Using 13.56 and 27.12 MHz sputtering, the Ag films still have a higher deposition rate and a better fcc structure, but a non-uniform and coarse surface. Using 40.68 MHz sputtering, the Ag film has a moderate deposition rate and a better fcc structure, but a less smooth surface. Using 60 MHz sputtering, the Ag film has an uniform and smooth surface, but a low deposition rate and a poor fcc structure. The growth and structural properties of Ag films are related to the ions energy and flux density. Therefore, changing the driving frequency is a better way to control the growth and structure of the Ag films.
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Enhanced photon emission and pair production in laser irradiating plasmas

FengWAN ( 弯峰),1 Chong LV (吕冲),1 Moran JIA (贾漠然),1 and Baisong XIE (谢柏松) 1, 2
Accept: 2017-03-02
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Enhanced photon emission and pair production due to heavy ion mass in the interaction of an ultraintense laser with overdense plasmas has been explored by particle-in-cell simulation. It is found that plasmas with heavier ion mass can excite a higher and broader electrostatic eld, which causes the enhancement of backward photon emission. The pair yields are then enhanced due to the increase of backwards photons colliding with incoming laser pulse. By examining the density evolution and angle distribution of each particle species, the origin of pair yields enhancement has been clari ed.
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The precision control method for plasma electron density and faraday rotation angle measurement on HL-2A

Wei ZHANG (张伟)1,2, Tongyu WU (吴彤宇)1,2, Baogang DING (丁宝钢)3, Yonggao LI (李永高)4, Yan ZHOU (周艳)4, Zejie YIN (阴泽杰)1,2
Accept: 2017-03-02
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The precision of Plasma Electron Density and Faraday Rotation Angle Measurement is a key indicator for Far-infrared (FIR) laser interferometers/polarimeter plasma diagnose. To improve the precision, a new multi-channel high Signal-to-Noise Ratio (SNR) HCOOH interferometer/polarimeter has been developed on HL-2A tokamak. It has a higher level requirement for phase demodulation precision. This paper introduces an improved real-time Fast Fourier Transform (FFT) algorithm based on Field Programmable Gate Array (FPGA) which significantly improves the precision. We also applied Real-time Error Monitoring Module (REMM) and Stable Error Inhibiting Module (SEIM) for precision control to deal with the weak signal. The interferometers/polarimeter with such improved precision control method has been tested in plasma discharge experiments and simulation experiments. The experimental results have confirmed that the plasma electron density precision is better than 1/3600 fringe and the faraday rotation angle measurement precision is better than 1/900 fringe while the temporal resolution is 80 ns. This performance could fully meet the requirements of HL-2A.
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Decay Characters of Charges on Insulator Surface after Different Types of Discharges

Cheng PAN (潘成)1, Ju TANG (唐炬)1,2, Dibo WANG (王邸博)3, Yi LUO (罗毅)1, Ran ZHUO(卓然)3, Mingli FU(傅明利)3
Accept: 2017-02-28
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In an insulating system including solid and gas dielectrics, discharge type has a strong impact on charge accumulation at the interface between two dielectrics, and hence charge decay. In order to clarify the influence, a surface charge measurement system was constructed, and three types of discharges, i.e. surface discharge, low intensity and high intensity coronas, were introduced to cause surface charge accumulation. The decay behavior of surface charges after different types of discharge was obtained at various temperatures. It is found that total surface charges monotonically decreased with time, and the decay rate became larger as temperature increased. However, after a surface discharge or a high intensity corona, surface charge density at local area appeared fluctuant during the decay process. Compared with this, the fluctuation of surface charge density was not observed after a low intensity corona. The mechanisms of surface charge accumulation and decay were analysed. Moreover, a microscopic physical model involving charge production, accumulation and decay was proposed so that the experimental results could be explained.