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Analysis of inverse synthetic aperture radar imaging in the presence of time-varying plasma sheath

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plasma Science and Technology 2022年第3期24卷 19-32页

作者：谢曜聪李小平沈方芳白博文刘彦明陈旭阳石磊 School of Aerospace Science and Technology Xidian UniversityXi'an 710071People's Republic of China

The plasma sheath can induce radar signal modulation,causing not only ineffective target detection,but also defocusing in inverse synthetic aperture radar(ISAR)imaging.In this paper,through establishing radar echo models of the reentry object enveloped with time-varying plasma sheath,we simulated the defocusing of ISAR images in typical environment.Simulation results suggested that the ISAR defocusing is caused by false scatterings,upon which the false scatterings’formation mechanism and distribution property are analyzed and studied.The range of false scattering correlates with the electron density fluctuation frequency.The combined value of the electron density fluctuation and the pulse repetition frequency jointly determines the Doppler of false scattering.Two measurement metrics including peak signal-to-noise ratio and structural similarity are used to evaluate the influence of ISAR imaging.

关键词： ISAR imaging plasma sheath time-varying transmission line matrix defocusing

Analysis of the influence of sheath positions,flight parameters and incident wave parameters on the wave propagation in plasma sheath

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plasma Science and Technology 2022年第3期24卷 33-40页

作者：张启凡韩一平董秦鲁董畅 School of Physics and Optoelectronic Engineering Xidian UniversityXi'an 710071People's Republic of China

The plasma sheath covering hypersonic vehicles has a significant effect on the propagation of electromagnetic waves.Based on the calculation of the flow field of a conical cylindrical,this work studies the propagation of electromagnetic waves in plasma sheath at L-band and Ku-band,and discusses the propagation characteristics in the head,side and tail of the sheath.The dielectric properties of plasma sheath are related to flight speed and altitude.A flight condition corresponds to a unique distribution of dielectric properties.For the conical cylindrical,the results show that flight speed is generally negatively correlated with the transmissivity of the plasma sheath.The reflection characteristics of electromagnetic waves at the L-band and Kuband when obliquely incident to the plasma sheath show a downward trend.When the frequency is increased to Ku-band,the propagation characteristics of electromagnetic waves in the plasma sheath are related to the position of the sheath.

关键词： plasma sheath reflection and transmission flow field

Adaptive protograph-based BICM-ID relying on the RJ-MCMC algorithm:a reliable and efficient transmission solution for plasma sheath channels

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plasma Science and Technology 2022年第4期24卷 96-105页

作者：刘彦明魏海亮石磊姚博 Key Laboratory of Information and Structure Efficiency in Extreme Environment Ministry of Education of ChinaXi'an 710071People's Republic of China School of Aerospace Science and Technology Xidian UniversityXi'an 710071People's Republic of China

For reentry communication,owing to the influence of the highly dynamic plasma sheath(PS),the parasitic modulation effect can occur and the received phase shift keying(PSK)signal constellation can be severely rotated,leading to unacceptable demodulation performance degradation.In this work,an adaptive non-coherent bit-interleaved coded modulation with iterative decoding(BICM-ID)system with binary PSK(BPSK)modulation and protograph lowdensity parity-check under the PS channel is proposed.The proposed protograph-based BICMID(P-BICM-ID)system can achieve joint processing of demodulation and decoding,where the soft information is adaptively estimated by reversible-jump Markov chain Monte Carlo(RJMCMC)algorithms.Simulation results indicate that compared to existing algorithms,the proposed system can adapt well to the dynamic characteristics of the PS channel and can obtain a 5dB performance improvement at a bit error rate of 10^(-6).

关键词： plasma sheath BICM-ID Markov model joint demodulation and decoding

Modeling of magnetized collisional plasma sheath with nonextensive electron distribution and ionization source

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plasma Science and Technology 2023年第3期25卷 21-31页

作者：陈龙杨叶慧安宇豪段萍孙少娟崔作君阚子晨高维富 School of Science Dalian Maritime UniversityDalian 116026People’s Republic of China

The properties of an atmospheric-pressure collisional plasma sheath with nonextensively distributed electrons and hypothetical ionization source terms are studied in this work. The Bohm criterion for the magnetized plasma is extended in the presence of an ion–neutral collisional force and ionization source. The effects of electron nonextensive distribution, ionization frequency, ion–neutral collision, magnetic field angle and ion temperature on the Bohm criterion of the plasma sheath are numerically analyzed. The fluid equations are solved numerically in the plasma–wall transition region using a modified Bohm criterion as the boundary condition. The plasma sheath properties such as charged particle density, floating sheath potential and thickness are thoroughly investigated under different kinds of ion source terms, contributions of collisions, and magnetic fields. The results show that the effect of the ion source term on the properties of atmosphericpressure collisional plasma sheath is significant. As the ionization frequency increases, the Mach number of the Bohm criterion decreases and the range of possible values narrows. When the ion source is considered, the space charge density increases, the sheath potential drops more rapidly,and the sheath thickness becomes narrower. In addition, ion–neutral collision, magnetic field angle and ion temperature also significantly affect the sheath potential profile and sheath thickness.

关键词： plasma sheath Bohm criterion nonextensivity ionization source

Characteristics of the plasma sheath in helium discharge within dielectric tubes

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plasma Science and Technology 2023年第4期25卷 79-92页

作者：吴淑群郭玥欧阳帆周保伟胡彪程鹤 College of Automation Engineering Nanjing University of Aeronautics and AstronauticsNanjing 211106People's Republic of China School of Chemistry and Chemical Engineering Nanjing University of Science and TechnologyNanjing 210094People's Republic of China

To understand the characteristics of the plasma sheath within small tubes,a 2D numerical model of He discharge within dielectric tubes is developed.During plasma propagation for a tube diameter of 0.05 mm,the sheath thickness in the plasma head is almost equal to the tube radius.It decreases rapidly to several micrometers at an axial distance of 0.05 mm behind the plasma head,and then slightly increases and saturates at the axial position far behind the plasma head.A plasma-gas sheath surrounding the central plasma column is observed for a tube diameter equal to or greater than 0.8 mm.It is replaced by a plasma-wall sheath for smaller tubes.With the decrease in the tube diameter,the sheath thickness far behind the plasma head decreases while the ion flux increases significantly.However,when O_(2)gas with a proportion of 2%is added,both the sheath thickness and ion flux decrease.

关键词： plasma sheath plasma modification helium discharge ion flux plasma jet

Sub-THz signals' propagation model in hypersonic plasma sheath under different atmospheric conditions

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Science China(Information Sciences) 2017年第11期60卷 242-252页

作者： Kai YUAN Yuhao WANG Linfang SHEN Ming YAO Xiaohua DENG Fuhui ZHOU Zhou CHEN Institute of Space Science and Technology Nanchang University Information Engineering School Nanchang University

One of the aims for modern hypersonic cruise flight is hypersonic global reach. The length of route for such flights could be up to thousands of kilometers. The atmospheric conditions on the route are complicated. On the other hand, hypersonic flights used to suffer from communication blackout. The sub-THz communication is considered as a potential solution to the ‘blackout’. In the present study the propagation for sub-THz signals in hypersonic plasma sheaths was modeled under different atmospheric conditions. According to the study, the electron density and the electron collision frequency near the onboard antenna linearly increase with the atmospheric mass density around the vehicle, hence the attenuation of sub-THz signals in hypersonic plasma sheaths increases with the atmospheric mass density. The impact led by the atmospheric temperature is ignorable. Based on the study a new sub-THz signals’ propagation model was developed, which could be utilized for quick estimation for signal propagation under different atmospheric conditions. The geographical difference of signal propagation over the whole globe was obtained with the new model. The results showed that the signal attenuation in plasma sheaths varies with latitude and longitude. The maximum signal attenuation occurs in Alaska, Canada and Russia.

关键词： sub-THz communication hypersonic cruise flight communication blackout plasma sheath signal propagation model signal attenuation

The Electrostatic Cylindrical sheath in a plasma

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plasma Science and Technology 2004年第2期6卷 2247-2249页

作者：王春华孙晓霞白冬雪 State Key Laboratory of Materials Modification by Laser Electron and Ion Beams Dalian University of Technology Dalian 116024 China

The electrostatic sheath with a cylindrical geometry in an ion-electron plasma is investigated. Assuming a Boltzmann response to electrons and cold ions with bulk flow, it is shown that the radius of the cylindrical geometry do not affect the sheath potential significantly. We also found that the sheath potential profile is steeper in the cylindrical sheath compared to the slab sheath. The distinct feature of the cylindrical sheath is that the ion density distribution is not monotonous. The sheath region can be divided into three regions, two ascendant regions and one descendant region.

关键词： plasma sheath ion-electron plasma

Effects of some parameters on the divertor plasma sheath characteristics and fuel retention in castellated tungsten tile gaps

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Chinese Physics B 2014年第11期23卷 403-409页

作者：桑超峰戴舒宇孙继忠 Bonnin Xavier 徐倩丁芳王德真 Key Laboratory of Materials Modification by Laser Ion and Electron Beams (Ministry of Education)School of Physics and Optoelectronic Engineering Dalian University of Technology LSPM-CNRS Universit Paris 13 Sorbonne Paris Cit Villetaneuse 93430 France Institute of plasma Physics Chinese Academy of Sciences

Castellation of plasma facing components is foreseen as the best solution for ensuring the lifetime of future fusion devices. However, the gaps between the resulting surface elements can increase fuel retention and complicate fuel removal issues. To know how the fuel is retained inside the gaps, the plasma sheath around the gaps needs to be understood first. In this work, a kinetic model is used to study plasma characteristics around the divertor gaps with the focus on the H＋ penetration depth inside the poloidal gaps, and a rate-theory model is coupled to simulate the hydrogen retention inside the tungsten gaps. By varying the magnetic field strength and plasma temperature, we find that the H＋ cyclotron radius has a significant effect on the penetration depth. Besides, the increase of magnetic field inclination angle can also increase the penetration depth. It is found in this work that parameters as well as the penetration depth strongly affect fuel retention in tungsten gaps.

关键词： divertor gaps penetration depth plasma sheath fuel retention

Inverse synthetic aperture radar range profile compensation of plasma-sheath-enveloped reentry object

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plasma Science and Technology 2022年第7期24卷 148-161页

作者：谢曜聪李小平沈方芳白博文石磊陈旭阳 School of Aerospace Science and Technology Xidian UniversityXi'an 710071People's Republic of China

The scattering points in a plasma sheath characterized with coupled velocities can cause pulse compression mismatching,which results in displacement and energy diffusion in the onedimension range profile.To solve this problem,we deduce the echo model of the plasma-sheathenveloped reentry object.By estimating the coupled velocities,we propose a compensation method to correct the defocus of an inverse synthetic aperture radar(ISAR)image in range dimension to improve the quality of the ISAR images.The simulation results suggest that the echoes from different regions of the surface of the reentry object have various coupling velocities,and the higher the coupled velocity,the more serious the displacement and energy diffusion in the range dimension.Our proposed method can correct the range dimension aberration.Two measurement metrics were used to evaluate the improvement of the compensation method.

关键词： plasma sheath inverse synthetic aperture radar imaging defocus coupled velocity reentry object