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Plasma Sci. Technol.  
  Plasma Sci. Technol.--2019, 21 (2)   Published: 29 December 2018
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Achievement of 1000 s plasma generation of RF source for neutral beam injector Hot!

Chundong HU (胡纯栋), Yahong XIE (谢亚红), Yongjian XU (许永建), et al.
Plasma Sci. Technol. 2019, 21 (2): 022001 ;  doi: 10.1088/2058-6272/aaf1e0
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A radio frequency (RF) ion source was developed for neutral beam injector in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). A cylindrical driver based RF plasma source was tested and optimized for long pulse operation. Recently, the plasma source achieved 1000 s stable plasma discharge with RF power of 35 kW and source pressure of 0.7 Pa for the first time. The heat loading on each of driver components such as the Faraday shield (FS), RF coil and expansion chamber was measured by the water flow calorimeter system. The experiment results showed that FS is the component with highest heat loading and the heat loading on FS was about 65.8% of total heat loading on source. The details of the long pulse operation of RF plasma source are presented in this paper.
Basic Plasma Phenomena

Finite-thickness effect of the fluids on bubbles and spikes in Richtmyer–Meshkov instability for arbitrary Atwood numbers

Wanhai LIU (刘万海)1, Changping YU (于长平) 2,5, Pei WANG (王裴) 3, et al.
Plasma Sci. Technol. 2019, 21 (2): 025001 ;  doi: 10.1088/2058-6272/aaee0c
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This paper investigates the finite-thickness effect of two superimposed fluids on bubbles and spikes in Richtmyer–Meshkov instability (RMI) for arbitrary Atwood numbers by using the method of the small parameter expansion up to the second order. When the thickness of the two fluids tends to be infinity, our results can reproduce the classical results where RMI happens at the interface separating two semi-infinity-thickness fluids of different densities. It is found that the thickness has a large influence on the amplitude evolution of bubbles and spikes compared with those in classical RMI. Based on the thickness relationship of the two fluids, the thickness effect on bubbles and spikes for four cases is discussed. The thickness encourages (or reduces) the growth of bubbles or spikes, depending on not only Atwood number, but also the relationship of the thickness ratio of the heavy and light fluids, which is explicitly determined in this paper.

Magnetically Confined Plasma

Loss-cone instabilities for compact fusion reactor and field-reversed configuration

Zhongtian WANG (王中天)1,2, Huidong LI (李会东)1 and Xueke WU (吴雪科)1
Plasma Sci. Technol. 2019, 21 (2): 025101 ;  doi: 10.1088/2058-6272/aaead9
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Loss-cone instabilities are studied for linear fusion devices. The gyro-kinetic equation for such a configuration is rigorously constructed in terms of action-angle variables by making use of canonical transformation. The dispersion relation, including for the first time, finite bounce frequency is obtained and numerically solved. The loss-cone modes are found near ion-cyclotron frequency. The growth rates are greatly reduced and approaching zero with increasing beta value. The results suggest that loss-cone instabilities are unlikely to be threatening to linear fusion devices since a new longitudinal invariant is found and gives a constraint which helps confinement.

Study of first orbit losses of 1 MeV tritons using the Lorentz orbit code in the LHD

Kunihiro OGAWA 1,2, Mitsutaka ISOBE 1,2, Takeo NISHITANI 1, et al.
Plasma Sci. Technol. 2019, 21 (2): 025102 ;  doi: 10.1088/2058-6272/aaeba8
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Shot-integrated measurement of the triton burnup ratio has been performed in the Large Helical Device. It was reported that the triton burnup ratio, defined as total DT neutron yield divided by total DD neutron yield, increases significantly in inward shifted configurations. To understand the magnetic configuration dependence of the triton burnup ratio, the first orbit loss fraction of 1MeV tritons is evaluated by means of the Lorentz orbit code for various magnetic configurations. The first orbit loss of 1 MeV tritons is seen at t of less than 10−5 s and loss points of the triton are concentrated on the side of the helical coil case where the magnetic field is relatively weak. The significant decrease of the first orbit loss fraction by 15% is obtained with the inward shift of the magnetic axis position from 3.90 to 3.55 m. It is found that the decrease of first orbit loss is due to the reduction of the first orbit loss of transition and helically trapped tritons.

Astrophysics and Space Plasma

Plasma discharge characteristics of segmented diverter strips subject to lightning strike Hot!

Han CHEN (陈汉)1, Fusheng WANG (王富生)1, Xiu XIONG (熊秀)2, et al.
Plasma Sci. Technol. 2019, 21 (2): 025301 ;  doi: 10.1088/2058-6272/aaeba9
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In order to research segmented diverters for aircraft lightning protection, a transient 2D multiphysics model based on magnetohydrodynamics theory is proposed to predict the location of the arc plasma discharge and lightning channel, and to simulate the electrothermal behavior. Based on numerical calculation and preliminary analysis, factors that affect the breakdown voltage of the segmented diverter are discussed. The results show that the voltage increase rate of the voltage source, the width of the air gap between metal segments and the geometry of these segments influence the breakdown voltage of the strip. High-voltage tests of the segmented diverter are performed to reveal air breakdown of the strip and redirect the lightning current. Experimental and numerical results are compared to verify the correctness of the numerical model. The ionization of the air gap between metal segments and the breakdown voltage of the strip calculated by the model are qualitatively consistent with experimental results. The breakdown voltage of the segmented diverter is far lower than the lightning voltage. When a lightning strike occurs, the segmented diverter can be quickly ionized to form a plasma channel which can guide the lightning current well.

Study on volt-ampere characteristics of solar array arcs in LEO spacecraft

Liying ZHU (朱立颖), Zhigang LIU (刘治钢), Xiaofeng ZHANG (张晓峰), et al.
Plasma Sci. Technol. 2019, 21 (2): 025302 ;  doi: 10.1088/2058-6272/aaf18a
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The primary and secondary arcs volt-ampere characteristics of low earth orbit solar arrays are studied in this research. Using three gallium-arsenide solar cell samples, the gap lengths of the solar cell are set to 1, 2, and 3 mm. First, the primary arc voltage characteristics of a solar array are analyzed. It is found that two steps are involved in the primary arc voltages, which are 116 and 22 V according to our experiment and are independent of the electrostatic discharge current and the gap lengths. By comparing with the arc pattern, we determined that current chopping may be the reason for the stepped arc voltage. Then, the characteristics of the secondary arc of the solar array are demonstrated. The study shows that the secondary arc voltage values increase with the gap length. In the case of the same cell with a fixed gap length, the voltage of the secondary arc increases with the string current. Finally, the relationship between the secondary arc voltage and the gap length is obtained which helps the string voltage and the gap length selection for system design.

Low Temperature Plasma

Experimental investigations of enhanced glow based on a pulsed hollow-cathode discharge

Chunxia LIANG (梁春霞), Ning WANG (王宁), Zhengchao DUAN (段正超), et al.
Plasma Sci. Technol. 2019, 21 (2): 025401 ;  doi: 10.1088/2058-6272/aaef49
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In this work, the pulsed hollow cathode discharges at low pressure argon with an axial magnetic field were studied. The results indicate that the pulsed discharge is operated in an enhanced glow (EG) mode. Under the same conditions, the discharge current of the pulsed discharge is two or three orders higher than that of the direct current discharge. The spatial and temporal evolution of the light emission shows that, the current fluctuation at the rising edge of the pulse plays an important role for the EG discharge of pulsed hollow cathode, which forms a high-density, high-current and long-distance plasma column outside the cavity.

OES diagnostic of radicals in 33 MHz radio-frequency Ar/C2H5OH atmospheric pressure plasma jet

Qianghua YUAN (袁强华), Pei REN (任佩), Yongjie ZHOU (周永杰),
Plasma Sci. Technol. 2019, 21 (2): 025402 ;  doi: 10.1088/2058-6272/aaebd1
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Ar/C2H5OH plasma jet is generated at atmospheric pressure by 33 MHz radio-frequency power source. This RF excitation frequencies which are higher than 13.56 MHz had rarely been used in atmospheric pressure plasma. The plasma characteristics of ethanol are investigated. The introduction of ethanol leads to the generation of four excited carbonaceous species C, CN, CH and C2 in plasma, respectively. Optical emission intensities of four carbonaceous species were strengthened with ethanol content increasing in the range of 0-4600 ppm. The ethanol content increase results in all the Ar spectra lines decrease. The reason is that the electron temperature decreases when ethanol content is high. The emission intensity ratios of C/C2, CN/C2 and CH/C2 decrease with the increase of ethanol content, showing that the relative amount of C2 is increasing by increasing the ethanol flow. The emission intensity ratios of excited species did not change much with the increase of RF power in stable discharge mode.

Electrical features of radio-frequency atmospheric pressure helium discharge with and without dielectric electrodes

Plasma Sci. Technol. 2019, 21 (2): 025403 ;  doi: 10.1088/2058-6272/aaede1
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A comparative study of radio-frequency atmospheric pressure glow discharge (rf APGD) generated in helium with and without dielectric electrodes to investigate the effect of electrodes insulation on electrical features of APGD is presented. In the α mode, both the rf APGDs remain volumetric, stable and uniform. In the γ mode, the APGD without dielectric electrodes shrinks into a constricted plasma column whereas APGD with dielectric electrodes remains stable and retains the same volume without plasma constriction even at higher densities of discharge current. A comparison of electrical features of both rf APGDs in normal and abnormal glow discharge regimes is presented. In both APGDs with and without dielectric electrodes, impedance measurements have been performed and compared with equivalent circuit models. The measured impedance data is found to be in good agreement with simulated data.

Plasma Technology

Evaluation of trans-ferulic acid degradation by dielectric barrier discharge plasma combined with ozone in wastewater with different water quality conditions

Jingyu REN (任景俞)1,2, Nan JIANG (姜楠)1,2,3, Kefeng SHANG (商克峰)1,2,3, et al.
Plasma Sci. Technol. 2019, 21 (2): 025501 ;  doi: 10.1088/2058-6272/aaef65
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In this study, dielectric barrier discharge plasma and ozone (O3) were combined to synergistically degrade trans-ferulic acid (FA), and the effect of water quality on FA degradation was studied. The results showed that 96.9% of FA was degraded after 40 min treatment by the plasma/O3 process. FA degradation efficiency increased with the pH values. The presence of suspended solid and humic acid inhibited FA degradation. FA degradation efficiency increased as the water temperature increased to 30 °C. However, the further increase in water temperature was adverse for FA degradation. Effects of common inorganic ions on FA degradation were also investigated. The addition of Cl - inhibited the FA degradation, while CO32 - had both negative and positive influences on FA degradation.  NO-3 and SO42 - did not have significant effect on FA degradation. Fe3+ and Cu2+ benefited FA degradation through the Fenton-like and catalytic ozonation reactions.

The properties of N-doped diamond-like carbon films prepared by helicon wave plasma chemical vapor deposition

Jiali CHEN (陈佳丽)1,2, Peiyu JI (季佩宇)1,2, Chenggang JIN (金成刚)1,2,3, et al.
Plasma Sci. Technol. 2019, 21 (2): 025502 ;  doi: 10.1088/2058-6272/aaee90
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In this paper, N-doped diamond-like carbon (DLC) films were deposited on silicon substrates by using helicon wave plasma chemical vapor deposition (HWP-CVD) with the Ar/CH4/N2 mixed gas. The surface morphology, structural and mechanical properties of the N-doped DLC films were investigated in detail by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), Raman spectra, and atomic force microscopy (AFM). It can be observed from SEM images that surface morphology of the films become compact and uniform due to the incorporation of N. The maximum of the deposition rate of the films is 143 nmmin-1 , which is related to the high plasma density. The results of XPS show that the N incorporates in the films and the C-C sp3 bond content increases firstly up to the maximum (20%) at 10 sccm of N2 flow rate, and then decreases with further increase in the N2 flow rate. The maximum Young’s modulus of the films is obtained by the doping of N and reaches 80 GPa at 10 sccm of N2 flow rate, which is measured by AFM in the scanning probe microscope mode. Meanwhile, friction characteristic of the N-doped DLC films reaches a minimum value of 0.010.

Experimental investigation on plasma jet deflection with magnetic fluid control based on PIV measurement

Kai ZHAO (赵凯)1,2, Baigang SUN (孙佰刚)3, Yongji LU (卢永吉) 2, et al.
Plasma Sci. Technol. 2019, 21 (2): 025503 ;  doi: 10.1088/2058-6272/aae09b
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This paper is devoted to experimentally investigating the influence of magnetic field intensity and gas temperature on the plasma jet deflection controlled by magneto hydrodynamics. The catalytic ionization seed CS2CO3 is injected into combustion gas by artificial forced ionization to obtain plasma fluid on a high-temperature magnetic fluid experimental platform. The plasma jet was deflected under the effect of an external magnetic field, forming a thrust-vector effect. Magnesium oxide was selected as a tracer particle, and a two-dimensional image of the jet flow field was collected using the particle image velocimetry (PIV) measurement method. Through image processing and velocity vector analysis of the flow field, the value of the jet deflection angle was obtained quantitatively to evaluate the thrust-vector effect. The variation of the jet deflection angle with the magnetic field intensity and gas temperature was studied under different experimental conditions. Experimental results show that the jet deflection angle increased gradually with a rise in gas temperature and then increased substantially when the gas temperature exceeded 2300 K. The jet deflection angle also increased with an increase in magnetic induction intensity. Experiments demonstrate it is feasible to use PIV test technology to study the thrust vector under magnetic control conditions.

Strengthening decomposition of oxytetracycline in DBD plasma coupling with Fe-Mn oxide-loaded granular activated carbon

Shoufeng TANG (唐首锋), Xue LI (李雪), Chen ZHANG (张晨), et al.
Plasma Sci. Technol. 2019, 21 (2): 025504 ;  doi: 10.1088/2058-6272/aaeba6
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A catalytic approach using a synthesized iron and manganese oxide-supported granular activated carbon (Fe-Mn GAC) under a dielectric barrier discharge (DBD) plasma was investigated to enhance the degradation of oxytetracycline (OTC) in water. The prepared Fe-Mn GAC was characterized by x-ray diffraction and scanning electron microscopy, and the results showed that the bimetallic oxides had been successfully spread on the GAC surface. The experimental results showed that the DBD + Fe-Mn GAC exhibited better OTC removal efficiency than the sole DBD and DBD + virgin GAC systems. Increasing the fabricated catalyst and discharge voltage was favorable to the antibiotic elimination and energy yield in the hybrid process. The coupling process could be elucidated by the ozone decomposition after Fe-Mn GAC addition, and highly hydroxyl and superoxide radicals both play significant roles in the decontamination. The main intermediate products were identified by HPLC-MS to study the mechanism in the collaborative system.

Synthesis of MoO3 by glow discharge in contact with water

Plasma Sci. Technol. 2019, 21 (2): 025505 ;  doi: 10.1088/2058-6272/aaf02b
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An atmospheric pressure glow discharge was ignited between a molybdenum anode and the water surface of a cathode for the synthesis of MoO3 powders. The action of glow discharge leads to the non-equilibrium evaporation of water, sputtering of the metal anode and formation of molybdenum (VI) oxide, which deposited on the anode. The chemical composition and morphology of the obtained powder were performed by using x-ray diffraction spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. It was found that the synthesized powders are pure α-MoO3. The possible mechanism of the formation of molybdenum trioxide during glow discharge treatment was described. The photocatalytic performance of MoO3 was estimated through the degradation of Rhodamine B under dark and UV irradiation conditions. Orthorhombic MoO3 exhibited the best photocatalytic activity for the photodegradation of Rhodamine B of 100% under UV irradiation for 15 min.

Fusion Engineering

Neutronic analysis of ITER radial x-ray camera

Luying NIU (牛璐莹), Hongrui CAO (曹宏睿), Kun XU (徐坤)
Plasma Sci. Technol. 2019, 21 (2): 025601 ;  doi: 10.1088/2058-6272/aaeba5
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The radial x-ray camera (RXC) is designed to measure the poloidal profile of plasma x-ray emission with high spatial and temporal resolution. The RXC diagnostic system consists of internal camera module and external camera module that view the core region and outer region through the vertical slots of the diagnostic first wall and diagnostics shield module of the equatorial port plug. To ensure the normal performance of the silicon photodiode array detectors of the cameras in the hard neutron irradiation environment in ITER tokamak, it is necessary to calculate neutron flux, radiation damage and the nuclear heating of the silicon photodiode array detectors and simulate the radiation maps of the range of RXC. This work estimated the nuclear environment of RXC based on Monte Carlo N-particle transport code, plasma scenarios of ITER tokamak and the RXC-integrated ITER CLITE model. The neutron flux of silicon photodiode array detectors and the lifetime of the silicon photodiode detector in the camera were calculated. The neutronic analysis results show that the shielding design has achieved the effect as expected and is able to guarantee the normal work of the detector during the ITER deuterium–deuterium phase without replacement, three detectors of the external camera can be operated during the whole deuterium–tritium phase without replacement.

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