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Plasma Sci. Technol.  
  Plasma Sci. Technol.--2017, 19 (8)   Published: 30 June 2017
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Electrodeless plasma thrusters for spacecraft: a review Hot!

Plasma Sci. Technol. 2017, 19 (8): 083001 ;  doi: 10.1088/2058-6272/aa71fe
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The physics of electrodeless electric thrusters that use directed plasma to propel spacecraft without employing electrodes subject to plasma erosion is reviewed. Electrodeless plasma thrusters are potentially more durable than presently deployed thrusters that use electrodes such as gridded ion, Hall thrusters, arcjets and resistojets. Like other plasma thrusters, electrodeless thrusters have the advantage of reduced fuel mass compared to chemical thrusters that produce the same thrust. The status of electrodeless plasma thrusters that could be used in communications satellites and in spacecraft for interplanetary missions is examined. Electrodeless thrusters under development or planned for deployment include devices that use a rotating magnetic field; devices that use a rotating electric field; pulsed inductive devices that exploit the Lorentz force on an induced current loop in a plasma; devices that use radiofrequency fields to heat plasmas and have magnetic nozzles to accelerate the hot plasma and other devices that exploit the Lorentz force. Using metrics of specific impulse and thrust efficiency, we find that the most promising designs are those that use Lorentz forces directly to expel plasma and those that use magnetic nozzles to accelerate plasma.

The 3rd Chinese laser and microwave aided plasma diagnostics workshop

Optimization of the optical system for electron cyclotron emission imaging diagnostics on the HL-2A tokamak

Min JIANG (蒋敏)1,3, Zhongbing SHI (石中兵)1 and Yilun ZHU (朱逸伦)2
Plasma Sci. Technol. 2017, 19 (8): 084001 ;  doi: 10.1088/2058-6272/aa62f7
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The optical system of the electron cyclotron emission imaging diagnostics on the HL-2A tokamak has been optimized in both the narrow zoom pattern and the wide zoom pattern. The two main features of the improved optical system are (1) larger coverage of the measurement region in the plasma and (2) a flatter imaging surface. The new optics has good focal characteristics over the whole plasma cross section. The curvature of the field of the image surface (ΔR between the core channel and the edge channel) is within 5.3 cm in the narrow zoom pattern and 6.7 cm in the wide zoom pattern after optimization, whereas the values with the present optics were 23 cm in the narrow zoom pattern and 15 cm in the wide zoom pattern. The optics will be fabricated, tested and
installed on the HL-2A tokamak before the next experimental campaign.

An accurate automated technique for quasi-optics measurement of the microwave diagnostics for fusion plasma

Jianqiang HU (胡健强), Ahdi LIU (刘阿娣), Chu ZHOU (周楚), Xiaohui ZHANG (张小辉), Mingyuan WANG (王明远), Jin ZHANG (张津), Xi FENG (冯喜), Hong LI (李弘), Jinlin XIE (谢锦林), Wandong LIU (刘万东) and Changxuan YU (俞昌旋)
Plasma Sci. Technol. 2017, 19 (8): 084002 ;  doi: 10.1088/2058-6272/aa6794
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A new integrated technique for fast and accurate measurement of the quasi-optics, especially for the microwave/millimeter wave diagnostic systems of fusion plasma, has been developed. Using the LabVIEW-based comprehensive scanning system, we can realize not only automatic but also fast and accurate measurement, which will help to eliminate the effects of temperature drift and standing wave/multi-reflection. With the Matlab-based asymmetric two-dimensional Gaussian fitting method, all the desired parameters of the microwave beam can be obtained. This technique can be used in the design and testing of microwave diagnostic systems such as reflectometers and the electron cyclotron emission imaging diagnostic systems of the Experimental Advanced Superconducting Tokamak.

Development of an HCN dual laser for the interferometer on EAST

Gen LI (李根)1, Xuechao WEI (魏学朝)2, Haiqing LIU (刘海庆)2, Junjie SHEN (申俊杰)1, Yinxian JIE (揭银先)2, Hui LIAN (连辉)2,
Plasma Sci. Technol. 2017, 19 (8): 084003 ;  doi: 10.1088/2058-6272/aa667b
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A two-color continuous wave (CW) discharge-pumped far-infrared (FIR) hydrogen cyanide (HCN) laser was developed as the source of an interferometer for measuring the line-averaged electron density in the Experimental Advanced Superconducting Tokamak (EAST). The output power of the dual laser system was about 120mW from each laser on the 337 μm (0.89 THz) line. The polarization of each output beam was fixed using thin tungsten filaments and oscillated
in the EH11 mode. Different megahertz intermediate frequencies (IF) and a slight frequency offset (∼1 MHz) were generated in this system to replace the traditional rotating grating with ∼10 kHz IF, and this can improve the time resolution of the interferometer significantly. The experimental result showed that different IF signals were obtained by successfully adjusting the cavity length. In particular, the beat frequency was captured at ∼1.3 MHz by a Schottky mixer when the length of the resonant cavities was changed by 5 μm by an automatic adjustment system. In order to study the character of IF, a long time record of the IF signal was carried out, and the IF signal could be stabilized for a few minutes in the range of 2 MHz to 3 MHz. A realtime IF stability control system was initially designed for long pulse discharge experiments on the EAST. The ∼MHz frequency response and good phase sensitivity of the dual laser HCN interferometer will allow the system to track fast density profiles and resolve fast MHD events, such as tearing/neoclassical tearing, disruptions, etc.

A digital wide range neutron flux measuring system for HL-2A

Chen YUAN (袁晨)1,2, Jun WU (吴军)1,2 and Zejie YIN (阴泽杰)1,2
Plasma Sci. Technol. 2017, 19 (8): 084004 ;  doi: 10.1088/2058-6272/aa6bf1
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To achieve wide-range, high-integration, and real-time performance on the neutron flux measurement on the HL-2A tokamak, a digital neutron flux measuring (DNFM) system based on the peripheral component interconnection (PCI) eXtension for Instrumentation express (PXIe) bus was designed. This system comprises a charge-sensitive preamplifier and a field programmable gate array (FPGA)-based main electronics plug-in. The DNFM totally covers source-range and intermediate-range neutron flux measurements, and increases system integration by a large margin through joining the pulse-counting mode and Campbell mode. Meanwhile, the neutron flux estimation method based on pulse piling proportions is able to choose and switch measuring modes in accordance with current
flux, and this ensures the accuracy of measurements when the neutron flux changes suddenly. It has been demonstrated by simulated signals that the DNFM enhances the full-scale measuring range up to 1.9×108 cm−2 s−1, with relative error below 6.1%. The DNFM has been verified to provide a high temporal sensitivity at 10ms time intervals on a single fission chamber on HL-2A.

An intelligent remote control system for ECEI on EAST

Dongxu CHEN (陈东旭), Yilun ZHU (朱逸伦), Zhenling ZHAO (赵朕领), Chengming QU (渠承明), Wang LIAO (廖望), Jinlin XIE (谢锦林) and Wandong LIU (刘万东)
Plasma Sci. Technol. 2017, 19 (8): 084005 ;  doi: 10.1088/2058-6272/aa6e4a
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An intelligent remote control system based on a power distribution unit (PDU) and Arduino has been designed for the electron cyclotron emission imaging (ECEI) system on Experimental Advanced Superconducting Tokamak (EAST). This intelligent system has three major functions: ECEI system reboot, measurement region adjustment and signal amplitude optimization. The observation region of ECEI can be modified for different physics proposals by remotely tuning
the optical and electronics systems. Via the remote adjustment of the attenuation level, the ECEI intermediate frequency signal amplitude can be efficiently optimized. The remote control system provides a feasible and reliable solution for the improvement of signal quality and the efficiency of the ECEI diagnostic system, which is also valuable for other diagnostic systems.

Magnetically Confined Plasma

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
Plasma Sci. Technol. 2017, 19 (8): 085101 ;  doi: 10.1088/2058-6272/aa6a50
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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 Mjølhus 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.

Effects of kinetic profiles on neutron wall loading distribution in CFETR

Wenjun YANG (杨文军)1,2,Guoqiang LI (李国强)1, Yanqiang HU (胡砚强)1, Songlin LIU (刘松林)1, Hang LI (李航)1 and Xiang GAO (高翔)1
Plasma Sci. Technol. 2017, 19 (8): 085102 ;  doi: 10.1088/2058-6272/aa6795
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The China Fusion Engineering Test Reactor (CFETR) is under design, which aims to bridge the gaps between ITER and the future fusion power plant. The neutron wall loading (NWL) depends on the neutron source distribution, which depends on the density and temperature profiles. In this paper, we calculate the NWL of CFETR and study the effects of density and temperature profiles on the NWL distribution along the first wall. Our calculations show that for a 200 MW fusion power, the maximum NWL is at the outer midplane and the vaule is about 0.4 MW m−2. The density and temperature profiles have little effect on the NWL distribution. The value of NWL is determined by the total fusion power.

Electrical and optical measurements in the early hydrogen discharge of GLAST-III

Plasma Sci. Technol. 2017, 19 (8): 085103 ;  doi: 10.1088/2058-6272/aa68db
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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, initiated with electron cyclotron heating (ECH). Diagnostic measurements provide insights into expected and unexpected physics issues related to the initial phase of discharge. A triple Langmuir probe (TLP) has been developed to measure time series of the floating potential, plasma electron temperature and number density over the entire discharge, allowing monitoring of the two phases of the discharge: the ECH pre-ionization phase following by the plasma current formation phase. A TLP has the ability to give time-resolved measurements of the floating potential (Vfloat), electron temperature (Te) and ion saturation current (Isat ∝ nekTe). The evolution of the ECH-assisted pre-ionization and subsequent plasma current phases in one shot are well envisioned by the probe. Intense fluctuations in the plasma current phase advocate for efficient equilibrium and feedback control systems. Moreover, the emergence of some strong impurity lines in the emission spectrum, even after only a few shots, suggests a crucial need for improvements in the base vacuum level. A noticeable change in the shape of the temporal profiles of the floating potential, electron temperature, ion saturation current (Isat) and light emission has been observed with changing hydrogen fill pressure and vertical magnetic field.

Low Temperature Plasma

Quantitative relationship between the maximum streamer length and discharge voltage of a pulsed positive streamer discharge in water

Xiaoqiong WEN (温小琼)1, Qian LI (李倩), Jingsen LI (李井森) and Chunsheng REN (任春生)
Plasma Sci. Technol. 2017, 19 (8): 085401 ;  doi: 10.1088/2058-6272/aa6bf0
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A linear relationship has been realized between the maximum streamer length and discharge voltage of a pulsed positive streamer discharge by measuring the streamer length in water with conductivity of 100 μS cm−1 using high-speed photography. Based on Ohm’s law, a quantitative equation has been derived for the dependence of the maximum streamer length on the discharge voltage of a pulsed positive streamer discharge in water. According to the equation, our results
suggest that the streamers spontaneously stop propagating through water due to the voltage at the streamer head dropping below the ignition voltage of a pulsed positive streamer discharge.

On peak current in atmospheric pulse-modulated microwave discharges by the PIC-MCC model

Yuantao ZHANG (张远涛), Yu LIU (刘雨) and Bing LIU (刘冰)
Plasma Sci. Technol. 2017, 19 (8): 085402 ;  doi: 10.1088/2058-6272/aa6a51
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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 a 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 high-energy electrons.

Plasma Technology

Plasma polymerized acetylene deposition using a return corona enhanced plasma reactor

Rokibul ISLAM1,3, Shuzheng XIE1, Karl R ENGLUND2 and Patrick D PEDROW1
Plasma Sci. Technol. 2017, 19 (8): 085501 ;  doi: 10.1088/2058-6272/aa6bef
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A corona based weakly ionized plasma source was developed to deposit plasma polymerized acetylene coating at atmospheric pressure. The plasma source included a distinctive point-topoint geometry consisting of an array of high voltage needles and an array of protrusions placed over a grounded screen. The geometry facilitated various corona discharge modes that included return corona to contribute plasma polymerized acetylene deposition downstream from the
corona section. Scanning probe techniques were used to investigate deposition on both the leading surface and the trailing surface of substrates. Deposition was initiated as distinct nodules that merged to form a thin plasma polymerized coating.

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)1 and Younian WANG (王友年)
Plasma Sci. Technol. 2017, 19 (8): 085502 ;  doi: 10.1088/2058-6272/aa6d4d
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Plasma atomic layer etching is proposed to attain layer-by-layer etching, as it has atomic-scale resolution, and can etch monolayer materials. In the etching process, ion energy and angular distributions (IEADs) bombarding the wafer placed on the substrate play a critical role in trench profile evolution, thus importantly flexibly controlling IEADs in the process. Tailored bias voltage waveform is an advisable method to modulate the IEADs effectively, and then improve the trench profile. In this paper, a multi-scale 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 obtaining more anisotropic trench profile.

Hydrophobic coating of surfaces by plasma polymerization in an RF plasma reactor with an outer planar electrode: synthesis, characterization and biocompatibility

Mustafa KARAMAN1,2,5, Mehmet GüRSOY1, Fatmanur AYKüL2, Zahide TOSUN3, M Demirel KARS2 and H Bekir YILDIZ4
Plasma Sci. Technol. 2017, 19 (8): 085503 ;  doi: 10.1088/2058-6272/aa6fec
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This paper presents the plasma polymerization of poly(hexafluorobutyl acrylate) (PHFBA) thin films on different substrates in an RF plasma reactor with an outer planar electrode. This reactor configuration allows large area uniformity and fast processing times. Deposition rates of up to 60 nm min−1 were observed. The influence of plasma power and substrate temperature on the deposition rate, structure and wettability of the as-deposited films was investigated. It was
observed that better hydrophobicity was obtained at high plasma power and in low temperature conditions. PHFBA thin films deposited on electrospun poly(acrylonitrile) fiber mats under such conditions resulted in superhydrophobic surfaces with contact angle values greater than 150°. In vitro cell studies using human epithelial cells demonstrated the non-toxic nature of the plasma-polymerized PHFBA films.

Control of growth and structure of Ag films by the 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 and Su ZHANG (张苏)3
Plasma Sci. Technol. 2017, 19 (8): 085504 ;  doi: 10.1088/2058-6272/aa6619
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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, a uniform and smooth surface and a good fcc structure. Using 13.56 and 27.12 MHz sputtering, the Ag films still have a high deposition rate and a good fcc structure, but a non-uniform and coarse surface. Using 40.68 MHz sputtering, the Ag film has a moderate deposition rate and a good fcc structure, but a less smooth surface. Using 60 MHz sputtering, the Ag film has a 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 good way to control the growth and structure of the Ag films.

A saw-tooth plasma actuator for film cooling efficiency enhancement of a shaped hole

Guozhan LI (李国占), Jianyang YU (俞建阳), Huaping LIU (刘华坪), Fu CHEN (陈浮) and Yanping SONG (宋彦萍)
Plasma Sci. Technol. 2017, 19 (8): 085505 ;  doi: 10.1088/2058-6272/aa6744
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This paper reports the large eddy simulations of the effects of a 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 sawtooth 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 3D plasma force vectors. The results show that thanks to the downward force and the momentum injection effect of the saw-tooth plasma actuator, the cold jet comes 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 the counter-rotating vortex pair (CRVP) 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 CRVP whose size and strength are smaller than those of the anti-counter rotating vortex pair in the 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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