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Wave field structure and power coupling features of blue-core helicon plasma driven by various antenna geometries and frequencies
Chao Wang(王超), Jia Liu(刘佳), Lei Chang(苌磊), Ling-Feng Lu(卢凌峰), Shi-Jie Zhang(张世杰), and Fan-Tao Zhou(周帆涛)
Chin. Phys. B, 2024, 33 (
3
): 035201. DOI:
10.1088/1674-1056/ad1486
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This paper deals with wave propagation and power coupling in blue-core helicon plasma driven by various antennas and frequencies. It is found that compared to non-blue-core mode, for blue-core mode, the wave can propagate in the core region, and it decays sharply outside the core. The power absorption is lower and steeper in radius for blue-core mode. Regarding the effects of antenna geometry for blue-core mode, it shows that half helix antenna yields the strongest wave field and power absorption, while loop antenna yields the lowest. Moreover, near axis, for antennas with
m
= +1, the wave field increases with axial distance. In the core region, the wave number approaches to a saturation value at much lower frequency for non-blue-core mode compared to blue-core mode. The total loading resistance is much lower for blue-core mode. These findings are valuable to understanding the physics of blue-core helicon discharge and optimizing the experimental performance of blue-core helicon plasma sources for applications such as space propulsion and material treatment.
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Three-dimensional magnetic reconnection in complex multiple X-point configurations in an ancient solar-lunar terrestrial system
Xiang-Lei He(何向磊), Ao-Hua Mao(毛傲华), Meng-Meng Sun(孙萌萌), Ji-Tong Zou(邹继同), and Xiao-Gang Wang(王晓钢)
Chin. Phys. B, 2024, 33 (
3
): 035202. DOI:
10.1088/1674-1056/ad0b02
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Magnetic reconnection processes in three-dimensional (3D) complex field configurations have been investigated in different magneto-plasma systems in space, laboratory, and astrophysical systems. Two-dimensional (2D) features of magnetic reconnection have been well developed and applied successfully to systems with symmetrical property, such as toroidal fusion plasmas and laboratory experiments with an axial symmetry. But in asymmetric systems, the 3D features are inevitably different from those in the 2D case. Magnetic reconnection structures in multiple celestial body systems, particularly star-planet-Moon systems, bring fresh insights to the understanding of the 3D geometry of reconnection. Thus, we take magnetic reconnection in an ancient solar-lunar terrestrial magneto-plasma system as an example by using its crucial parameters approximately estimated already and also some specific applications in pathways for energy and matter transports among Earth, ancient Moon, and the interplanetary magnetic field (IMF). Then, magnetic reconnection of the ancient lunar-terrestrial magnetospheres with the IMF is investigated numerically in this work. In a 3D simulation for the Earth-Moon-IMF system, topological features of complex magnetic reconnection configurations and dynamical characteristics of magnetic reconnection processes are studied. It is found that a coupled lunar-terrestrial magnetosphere is formed, and under various IMF orientations, multiple X-points emerge at distinct locations, showing three typical magnetic reconnection structures in such a geometry, i.e., the X-line, the triple current sheets, and the A-B null pairs. The results can conduce to further understanding of reconnection physics in 3D for plasmas in complex magnetic configurations, and also a possible mechanism for energy and matters transport in evolutions of similar astrophysical systems.
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Hollow cathode effect in radio frequency hollow electrode discharge in argon
Liu-Liang He(贺柳良), Feng He(何锋), and Ji-Ting Ouyang(欧阳吉庭)
Chin. Phys. B, 2024, 33 (
3
): 035203. DOI:
10.1088/1674-1056/ad1a89
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Radio frequency capacitively coupled plasma source (RF-CCP) with a hollow electrode can increase the electron density through the hollow cathode effect (HCE), which offers a method to modify the spatial profiles of the plasma density. In this work, the variations of the HCE in one RF period are investigated by using a two-dimensional particle-in-cell/Monte-Carlo collision (PIC/MCC) model. The results show that the sheath electric field, the sheath potential drop, the sheath thickness, the radial plasma bulk width, the electron energy distribution function (EEDF), and the average electron energy in the cavity vary in one RF period. During the hollow electrode sheath's expansion phase, the secondary electron heating and sheath oscillation heating in the cavity are gradually enhanced, and the frequency of the electron pendular motion in the cavity gradually increases, hence the HCE is gradually enhanced. However, during the hollow electrode sheath's collapse phase, the secondary electron heating is gradually attenuated. In addition, when interacting with the gradually collapsed hollow electrode sheaths, high-energy plasma bulk electrons in the cavity will lose some energy. Furthermore, the frequency of the electron pendular motion in the cavity gradually decreases. Therefore, during the hollow electrode sheath's collapse phase, the HCE is gradually attenuated.
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Numerical studies for plasmas of a linear plasma device HIT-PSI with geometry modified SOLPS-ITER
Min Wang(王敏), Qiuyue Nie(聂秋月), Tao Huang(黄韬), Xiaogang Wang(王晓钢), and Yanjie Zhang(张彦杰)
Chin. Phys. B, 2024, 33 (
3
): 035204. DOI:
10.1088/1674-1056/ad16d4
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The HIT-PSI is a linear plasma device built for physically simulating the high heat flux environment of future reactor divertors to test/develop advanced target plate materials. In this study, the geometry-modified SOLPS-ITER program is employed to examine the effects of the magnetic field strength and neutral pressure in the device on the heat flux experienced by the target plate of the HIT-PSI device. The findings of the numerical simulation indicate a positive correlation between the magnetic field strength and the heat flux density. Conversely, there is a negative correlation observed between the heat flux density and the neutral pressure. When the magnetic field strength at the axis exceeds 1 tesla and the neutral pressure falls below 10 Pa, the HIT-PSI has the capability to attain a heat flux of 10 MW·m
-2
at the target plate. The simulation results offer a valuable point of reference for subsequent experiments at HIT-PSI.
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Long radial coherence of electron temperature fluctuations in non-local transport in HL-2A plasmas
Zhongbing Shi(石中兵), Kairui Fang(方凯锐), Jingchun Li(李景春), Xiaolan Zou(邹晓岚), Zhaoyang Lu(卢兆旸), Jie Wen(闻杰), Zhanhui Wang(王占辉), Xuantong Ding(丁玄同), Wei Chen(陈伟), Zengchen Yang(杨曾辰), Min Jiang(蒋敏), Xiaoquan Ji(季小全), Ruihai Tong(佟瑞海), Yonggao Li(李永高), Peiwan Shi(施陪万), Wulyv Zhong(钟武律), and Min Xu(许敏)
Chin. Phys. B, 2024, 33 (
2
): 025202. DOI:
10.1088/1674-1056/ad1093
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The dynamics of long-wavelength ($k_\theta<1.4$ cm$^{-1}$), broadband (20 kHz-200 kHz) electron temperature fluctuations ($\tilde T_{\rm e}/T_{\rm e}$) of plasmas in gas-puff experiments are observed for the first time in HL-2A tokamak. In a relatively low density ($n_{\rm e}(0) \simeq 0.91 \times10^{19}$$\rm m^{-3}$-$1.20 \times10^{19}$$\rm m^{-3}$) scenario, after gas-puffing the core temperature increases and the edge temperature drops. On the contrary, temperature fluctuation drops at the core and increases at the edge. Analyses show the non-local emergence is accompanied with a long radial coherent length of turbulent fluctuations. While in a higher density ($n_{\rm e}(0) \simeq 1.83 \times10^{19}$ m$^{-3}$-$2.02 \times10^{19}$ m$^{-3}$) scenario, the phenomena are not observed. Furthermore, compelling evidence indicates that $\bm{E} \times \bm{B}$ shear serves as a substantial contributor to this extensive radial interaction. This finding offers a direct explanatory link to the intriguing core-heating phenomenon witnessed within the realm of non-local transport.
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Differences between two methods to derive a nonlinear Schrödinger equation and their application scopes
Yu-Xi Chen(陈羽西), Heng Zhang(张恒), and Wen-Shan Duan(段文山)
Chin. Phys. B, 2024, 33 (
2
): 025203. DOI:
10.1088/1674-1056/ad082b
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The present paper chooses a dusty plasma as an example to numerically and analytically study the differences between two different methods of obtaining nonlinear Schrödinger equation (NLSE). The first method is to derive a Korteweg-de Vries (KdV)-type equation and then derive the NLSE from the KdV-type equation, while the second one is to directly derive the NLSE from the original equation. It is found that the envelope waves from the two methods have different dispersion relations, different group velocities. The results indicate that two envelope wave solutions from two different methods are completely different. The results also show that the application scope of the envelope wave obtained from the second method is wider than that of the first one, though both methods are valuable in the range of their corresponding application scopes. It is suggested that, for other systems, both methods to derive NLSE may be correct, but their nonlinear wave solutions are different and their application scopes are also different.
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Electron characteristics and dynamics in sub-millimeter pulsed atmospheric dielectric barrier discharge
Junlin Fang(方骏林), Yarong Zhang(张亚容), Chenzi Lu(卢陈梓), Lili Gu(顾莉莉), Shaofeng Xu(徐少锋), Ying Guo(郭颖), and Jianjun Shi(石建军)
Chin. Phys. B, 2024, 33 (
1
): 015201. DOI:
10.1088/1674-1056/ad0118
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The discharge characteristics and mechanism of sub-millimeter pulsed dielectric barrier discharge in atmospheric-pressure helium are investigated experimentally and theoretically, demonstrating that when the discharge gap distance is reduced from 1.00 mm to 0.20 mm, the discharge ignition time is reduced to approximately 40 ns and discharge intensity is enhanced in terms of the discharge optical emission intensity and density of the plasma species, (energetic electrons with energy above 8.40 eV). The simulated results show that as the discharge gap distance is further reduced to 0.10 mm, the number of energetic electrons decreases, which is attributable to the contraction of plasma bulk regime and reduction of electron density in the discharge bulk. Conversely, the proportion of energetic electrons to the total electrons in the discharge monotonically increases as the discharge gap distance is reduced from 1.00 mm to 0.10 mm. It is proposed that a gap distance of 0.12 mm is optimal to achieve a high concentration and proportion of energetic electrons in sub-millimeter pulsed atmosphere dielectric barrier discharge.
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Numerical study of alpha particle loss with toroidal field ripple based on CFETR steady-state scenario
Niuqi Li(李钮琦), Yingfeng Xu(徐颖峰), Fangchuan Zhong(钟方川), and Debing Zhang(张德兵)
Chin. Phys. B, 2024, 33 (
1
): 015202. DOI:
10.1088/1674-1056/ad03de
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Effects of plasma equilibrium parameters on the alpha particle loss with the toroidal field ripple based on the CFETR steady-state scenario have been numerically investigated by the orbit-following code GYCAVA. It is found that alpha particle losses decrease and loss regions become narrower with the plasma current increasing or with the magnetic field decreasing. It is because the ripple stochastic transport and the ripple well loss of alpha particle are reduced with the safety factor decreasing. Decrease of the plasma density and temperature can reduce alpha particle losses due to enhancement of the slowing-down effect. The direction of the toroidal magnetic field can significantly affect heat loads induced by lost alpha particle. The vertical asymmetry of heat loads induced by the clockwise and counter-clockwise toroidal magnetic fields are due to the fact that the ripple distribution is asymmetric about the mid-plane, which can be explained by the typical orbits of alpha particle. The maximal heat load of alpha particle for the clockwise toroidal magnetic field is much smaller than that for the counter-clockwise one.
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Growth mechanism and characteristics of electron drift instability in Hall thruster with different propellant types
Long Chen(陈龙), Zi-Chen Kan(阚子晨), Wei-Fu Gao(高维富), Ping Duan(段萍), Jun-Yu Chen(陈俊宇), Cong-Qi Tan(檀聪琦), and Zuo-Jun Cui(崔作君)
Chin. Phys. B, 2024, 33 (
1
): 015203. DOI:
10.1088/1674-1056/acf9e5
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The existence of a significant electron drift instability (EDI) in the Hall thruster is considered as one of the possible causes of the abnormal increase in axial electron mobility near the outlet of the channel. In recent years, extensive simulation research on the characteristics of EDI has been conducted, but the excitation mechanism and growth mechanism of EDI in linear stage and nonlinear stage remain unclear. In this work, a one-dimensional PIC model in the azimuthal direction of the thruster near-exit region is established to gain further insights into the mechanism of the EDI in detail, and the effects of different types of propellants on EDI characteristics are discussed. The changes in axial electron transport caused by EDI under different types of propellants and electromagnetic field strengths are also examined. The results indicate that EDI undergoes a short linear growth phase before transitioning to the nonlinear phase and finally reaching saturation through the ion Landau damping. The EDI drives a significant ion heating in the azimuthal direction through electron--ion friction before entering the quasi-steady state, which increases the axial mobility of the electrons. Using lighter atomic weight propellant can effectively suppress the oscillation amplitude of EDI, but it will increase the linear growth rate, frequency, and phase velocity of EDI. Compared with the classical mobility, the axial electron mobility under the EDI increases by three orders of magnitude, which is consistent with experimental phenomena. The change of propellant type is insufficient to significantly change the axial electron mobility. It is also found that the collisions between electrons and neutral gasescan significantly affect the axial electron mobility under the influence of EDI, and lead the strength of the electric field to increase and the strength of the magnetic field to decrease, thereby both effectively suppressing the axial transport of electrons.
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Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker
Shi-Dong Peng(彭世东), Jing Li(李静), Wei Duan(段薇), Yun-Dong Cao(曹云东), Shu-Xin Liu(刘树鑫), and Hao Huang(黄浩)
Chin. Phys. B, 2024, 33 (
1
): 015204. DOI:
10.1088/1674-1056/acd7cb
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When the contacts of a medium-voltage DC air circuit breaker (DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V—12.33 V drops along the 17 μm space charge layer away from the cathode (65.5 kV/m—72.5 kV/m) when the current varies from 20 kA—80 kA. The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core, but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.
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Transition from a filamentary mode to a diffuse one with varying distance from needle to stream of an argon plasma jet
Hui-Min Xu(许慧敏), Jing-Ge Gao(高敬格), Peng-Ying Jia(贾鹏英), Jun-Xia Ran(冉俊霞), Jun-Yu Chen(陈俊宇), and Jin-Mao Li(李金懋)
Chin. Phys. B, 2024, 33 (
1
): 015205. DOI:
10.1088/1674-1056/ad0149
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Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often operates in a filamentary mode. Compared to the filamentary mode, the diffuse mode is more desirable for applications. Hence, many efforts have been exerted to accomplish the diffuse mode of the argon plasma jet. In this paper, a novel single-needle argon plasma jet is developed to obtain the diffuse mode. It is found that the plasma jet operates in the filamentary mode when the distance from the needle tip to the central line of the argon stream (
d
) is short. It transits to the diffuse mode with increasing
d
. For the diffuse mode, there is always one discharge pulse per voltage cycle, which initiates at the rising edge of the positive voltage. For comparison, the number of discharge pulse increases with an increase in the peak voltage for the filamentary mode. Fast photography reveals that the plasma plume in the filamentary mode results from a guided positive streamer, which propagates in the argon stream. However, the plume in the diffuse mode originates from a branched streamer, which propagates in the interfacial layer between the argon stream and the surrounding air. By optical emission spectroscopy, plasma parameters are investigated for the two discharge modes, which show a similar trend with increasing
d
. The diffuse mode has lower electron temperature, electron density, vibrational temperature, and gas temperature compared to the filamentary mode.
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Suppression of stimulated Brillouin and Raman scatterings using an alternating frequency laser and transverse magnetic fields
Rui-Jin Cheng(程瑞锦), Xiao-Xun Li(李晓旬), Qing Wang(王清), De-Ji Liu(刘德基), Zhuo-Ming Huang(黄卓明), Shuai-Yu Lv(吕帅宇), Yuan-Zhi Zhou(周远志), Shu-Tong Zhang(张舒童), Xue-Ming Li(李雪铭), Zu-Jie Chen(陈祖杰), Qiang Wang(王强), Zhan-Jun Liu(刘占军), Li-Hua Cao(曹莉华), and Chun-Yang Zheng(郑春阳)
Chin. Phys. B, 2024, 33 (
1
): 015206. DOI:
10.1088/1674-1056/ad0716
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A novel scheme to suppress both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) by combining an alternating frequency (AF) laser and a transverse magnetic field is proposed. The AF laser allows the laser frequency to change discretely and alternately over time. The suppression of SBS is significant as long as the AF difference is greater than the linear growth rate of SBS or the alternating time of the laser frequency is shorter than the linear growth time of SBS. However, the AF laser proves ineffective in suppressing SRS, which usually has a much higher linear growth rate than SBS. To remedy that, a transverse magnetic field is included to suppress the SRS instability. The electrons trapped in the electron plasma waves (EPWs) of SRS can be accelerated by the surfatron mechanism in a transverse magnetic field and eventually detrapped. While continuously extracting energy from EPWs, the EPWs are dissipated and the kinetic inflation of SRS is suppressed. The one-dimensional particle-in-cell simulation results show that both SBS and SRS can be effectively suppressed by combining the AF laser with a transverse magnetic field with tens of Tesla. The total reflectivity can be dramatically reduced by more than one order of magnitude. These results provide a potential reference for controlling SBS and SRS under the related parameters of inertial confinement fusion.
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The (1+1)-dimensional nonlinear ion acoustic waves in multicomponent plasma containing kappa electrons
Mai-Mai Lin(林麦麦), Lei Jiang(蒋蕾), and Ming-Yue Wang(王明月)
Chin. Phys. B, 2023, 32 (
12
): 125201. DOI:
10.1088/1674-1056/ace8f9
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Large amplitude (1+1)-dimensional nonlinear ion acoustic waves are theoretically studied in multicomponent plasma consisting of positively charged ions and negatively charged ions, ion beam, kappa-distributed electrons, and dust grains, respectively. By using the Sagdeev potential method, the dynamical system and the Sagdeev potential function are obtained. The important influences of system parameters on the phase diagram of this system are investigated. It is found that the linear waves, the nonlinear waves and the solitary waves are coexistent in the multicomponent plasma system. Meanwhile, the variations of Sagdeev potential with parameter can also be obtained. Finally, it seems that the propagating characteristics of (1+1)-dimensional nonlinear ion acoustic solitary waves and ion acoustic nonlinear shock wave can be influenced by different parameters of this system.
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Global simulation of plasma series resonance effect in radio frequency capacitively coupled Ar/O
2
plasma
Xue Bai(白雪), Hai-Wen Xu(徐海文), Chong-Biao Tian(田崇彪), Wan Dong(董婉), Yuan-Hong Song(宋远红), and You-Nian Wang(王友年)
Chin. Phys. B, 2023, 32 (
12
): 125203. DOI:
10.1088/1674-1056/ace427
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Radio frequency capacitively coupled plasmas (RF CCPs) play a pivotal role in various applications in etching and deposition processes on a microscopic scale in semiconductor manufacturing. In the discharge process, the plasma series resonance (PSR) effect is easily observed in electrically asymmetric and geometrically asymmetric discharges, which could largely influence the power absorption, ionization rate,
etc
. In this work, the PSR effect arising from geometrically and electrically asymmetric discharge in argon-oxygen mixture gas is mainly investigated by using a plasma equivalent circuit model coupled with a global model. At relatively low pressures, as Ar content (
α
) increases, the inductance of the bulk is weakened, which leads to a more obvious PSR phenomenon and a higher resonance frequency (
ω
psr
). When the Ar content is fixed, varying the pressure and gap distance could also have different effects on the PSR effect. With the increase of the pressure, the PSR frequency shifts towards the higher order, but in the case of much higher pressure, the PSR oscillation would be strongly damped by frequent electron-neutral collisions. With the increase of the gap distance, the PSR frequency becomes lower. In addition, electrically asymmetric waveforms applied to a geometrically asymmetric chamber may weaken or enhance the asymmetry of the discharge and regulate the PSR effect. In this work, the Ar/O
2
electronegative mixture gas is introduced in a capacitive discharge to study the PSR effect under geometric asymmetry effect and electrical asymmetry effect, which can provide necessary guidance in laboratory research and current applications.
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Speeding-up direct implicit particle-in-cell simulations in bounded plasma by obtaining future electric field through explicitly propulsion of particles
Haiyun Tan(谭海云), Tianyuan Huang(黄天源), Peiyu Ji(季佩宇), Mingjie Zhou(周铭杰), Lanjian Zhuge(诸葛兰剑), and Xuemei Wu(吴雪梅)
Chin. Phys. B, 2023, 32 (
12
): 125204. DOI:
10.1088/1674-1056/acf449
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The direct implicit particle-in-cell is a powerful kinetic method for researching plasma characteristics. However, it is time-consuming to obtain the future electromagnetic field in such a method since the field equations contain time-dependent matrix coefficients. In this work, we propose to explicitly push particles and obtain the future electromagnetic field based on the information about the particles in the future. The new method retains the form of implicit particle pusher, but the future field is obtained by solving the traditional explicit equation. Several numerical experiments, including the motion of charged particle in electromagnetic field, plasma sheath, and free diffusion of plasma into vacuum, are implemented to evaluate the performance of the method. The results demonstrate that the proposed method can suppress finite-grid-instability resulting from the coarse spatial resolution in electron Debye length through the strong damping of high-frequency plasma oscillation, while accurately describe low-frequency plasma phenomena, with the price of losing the numerical stability at large time-step. We believe that this work is helpful for people to research the bounded plasma by using particle-in-cell simulations.
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Numerical simulation study of ionization characteristics of argon dielectric barrier discharge
Guiming Liu(刘桂铭), Lei Chen(陈雷), Zhibo Zhao(赵智博), and Peng Song(宋鹏)
Chin. Phys. B, 2023, 32 (
12
): 125205. DOI:
10.1088/1674-1056/acc0f8
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In order to better analyze the characteristics of particle distribution and its influencing factors in the ionized space during the process of coaxial dielectric barrier discharge, a self-designed two-dimensional axisymmetric structure exciter was used to carry out optical diagnosis, with the electron temperature calculated through Gaussian fitting. A plasma model was applied to conduct research on the discharge process through numerical simulation, with the changes in electron density and electron temperature were analyzed by using different discharge parameters. The research results show that with an increase in discharge voltage, pressure inside the reactor and relative permittivity, the discharge process is promoted. In addition, a rise in current density leads to an increase in the number of charged particles on the surface of the medium during the discharge process, while a rise in discharge intensity causes an increase in the electron density. Electron temperature decreases due to the increased loss of collision energy between particles. These results were confirmed by comparing experimental data with simulation results.
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Compared discharge characteristics and film modifications of atmospheric pressure plasma jets with two different electrode geometries
Xiong Chen(陈雄), Xing-Quan Wang(王兴权), Bin-Xiang Zhang(张彬祥), Ming Yuan(袁明), and Si-Ze Yang(杨思泽)
Chin. Phys. B, 2023, 32 (
11
): 115201. DOI:
10.1088/1674-1056/ace768
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Atmospheric pressure plasma jet shows great potential for polymer film processing. The electrode geometry is the key factor to determine discharge characteristics and film modification of jets. In this paper, we compared the discharge characteristics and the film modifications of atmospheric pressure plasma jets with needle-ring electrode (NRE) and double-ring electrode (DRE). The results show that jet with NRE has stronger electric field intensity and higher discharge power, making it present more reactive oxygen particles and higher electron temperature, but its discharge stability is insufficient. In contrast, the jet with DRE has uniform electric field distribution of lower field intensity, which allows it to maintain stable discharge over a wide range of applied voltages. Besides, the modification results show that the treatment efficiency of PET film by NRE is higher than that by DRE. These results provide a suitable atmospheric pressure plasma jets device selection scheme for polymer film processing process.
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Transmission effects of high energy nanosecond lasers in laser-induced air plasma under different pressures
Wei-Min Hu(胡蔚敏), Kai-Xin Yin(尹凯欣), Xiao-Jun Wang(王小军), Jing Yang(杨晶), Ke Liu(刘可), Qin-Jun Peng(彭钦军), and Zu-Yan Xu(许祖彦)
Chin. Phys. B, 2023, 32 (
10
): 105201. DOI:
10.1088/1674-1056/acb0bf
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When a high energy nanosecond (ns) laser induces breakdown in the air, the plasma density generated in the rarefied atmosphere is much smaller than that at normal pressure. It is associated with a relatively lower absorption coefficient and reduces energy loss of the laser beam at low pressure. In this paper, the general transmission characterizations of a Joule level 10 ns 1064 nm focused laser beam are investigated both theoretically and experimentally under different pressures. The evolution of the electron density ($n_{\rm e}$), the changes in electron temperature ($T_{\rm e}$) and the variation of laser intensity ($I$) are employed for numerical analyses in the simulation model. For experiments, four optical image transfer systems with focal length ($f$) of 200 mm are placed in a chamber and employed to focus the laser beam and produce plasmas at the focus. The results suggest that the transmittance increases obviously with the decreasing pressure and the plasma channels on the transmission path can be observed by the self-illumination. The simulation results agree well with the experimental data. The numerical model presents that the maximum $n_{\rm e}$ at the focus can reach 10$^{19}$ cm$^{-3}$, which is far below the critical density ($n_{\rm c}$). As a result, the laser beam is not completely shielded by the plasmas.
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Efficient ion acceleration driven by a Laguerre-Gaussian laser in near-critical-density plasma
Jia-Xiang Gao(高嘉祥), Meng Liu(刘梦), and Wei-Min Wang(王伟民)
Chin. Phys. B, 2023, 32 (
10
): 105202. DOI:
10.1088/1674-1056/ace428
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86
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Laser-driven ion accelerators have the advantages of compact size, high density, and short bunch duration over conventional accelerators. Nevertheless, it is still challenging to generate ion beams with quasi-monoenergetic peak and low divergence in experiments with the current ultrahigh intensity laser and thin target technologies. Here we propose a scheme that a Laguerre-Gaussian laser irradiates a near-critical-density (NCD) plasma to generate a quasi-monoenergetic and low-divergence proton beam. The Laguerre-Gaussian laser pulse in an NCD plasma excites a moving longitudinal electrostatic field with a large amplitude, and it maintains the inward bowl-shape for dozens of laser durations. This special distribution of the longitudinal electrostatic field can simultaneously accelerate and converge the protons. Our particle-in-cell (PIC) simulation shows that the efficient proton acceleration can be realized with the Laguerre-Gaussian laser intensity ranging from $3.9\times {10}^{21}$ W$\cdot$cm$^{-2}$-$1.6\times 10^{22}$ W$\cdot$cm$^{-2}$ available in the near future, e.g., a quasi-monoenergetic proton beam with peak energy $\sim 115 $ MeV and divergence angles less than 5$^\circ$ can be generated by a $5.3\times 10^{21}$ W$\cdot $cm$^{-2}$ pulse. This work could provide a reference for the high-quality ion beam generation with PWclass laser systems available recently.
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Effects of plasma radiation on the nonlinear evolution of neo-classical tearing modes in tokamak plasmas with reversed magnetic shear
Shuai Jiang(姜帅), Zheng-Xiong Wang(王正汹), Lai Wei(魏来), and Tong Liu(刘桐)
Chin. Phys. B, 2023, 32 (
10
): 105203. DOI:
10.1088/1674-1056/acedf7
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82
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Effects of plasma radiation on the nonlinear evolution of neo-classical double tearing modes (NDTMs) in tokamak plasmas with reversed magnetic shear are numerically investigated based on a set of reduced magnetohydrodynamics (MHD) equations. Cases with different separations $\varDelta_{\rm rs} =\left| {r_{\rm s2} -r_{\rm s1} } \right|$ between the two same rational surfaces are considered. In the small $\varDelta_{\rm rs} $ cases, the plasma radiation destabilizes the NDTMs and makes the kinetic energy still grow gradually in the late nonlinear phase. Moreover, the NDTM harmonics with high mode numbers reach a high level in the presence of plasma radiation, forming a broad spectrum of MHD perturbations that induces a radially broadened region of MHD turbulence. As a result, the profiles of safety factors also enter a nonlinear oscillation phase. In the intermediate $\varDelta_{\rm rs} $ case, the plasma radiation can advance the explosive burst of kinetic energy that results from the fast driven reconnection between the two rational surfaces, because it can further promote the destabilizing effects of bootstrap current perturbation on the magnetic island near the outer rational surfaces. In the large $\varDelta_{\rm rs} $ case, through destabilizing the outer islands significantly, the plasma radiation can even induce the explosive burst in the reversed magnetic shear configuration where the burst cannot be induced in the absence of plasma radiation.
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