电子辐照下聚合物介质深层充电现象研究

空间辐射环境中,聚合物介质的深层充放电效应是威胁航天器安全的重要因素之一.文中在Chudleigh和von Berlepsch所发展的电位衰减模型基础上引入传输电流项,考虑了电子入射引起的感应电导率和感应电场的影响,提出了新的分析研究介质材料深层充电规律和特征的模型.通过该模型,分析了不同辐射条件下介质的表面电位、内部电荷与电场分布的变化,并设计实验及援引其他实验数据对模型分析结果进行验证.分析和实验结果表明,聚合物介质在深层充电过程中的平衡电位随着入射电子束流强度和介质电阻率的增加而增大,决定深层充电平 关键词： 深层充电 电荷传输模型 电子束 聚合物     

Experimental study of carbon particle charging at shock-wave pyrolysis of C3O2

The temporal variation in electron and ion concentrations have been measured in shock-heated mixtures of Ar + (0-2)% C₃O₂ in the 2000-3600 K temperature and 15-30 bar pressure range. Experiments in pure argon proved that the observed free electrons and ions originate from inherent impurities of sodium. The equilibrium concentrations of free charges in argon were established during (1-3) × 10⁻⁵ s and varied from 4 × 10¹¹ cm⁻³ at T₅ = 2500 K to 5 × 10¹² cm⁻³ at 3500 K. In the reactive mixtures, containing C₃O₂, the time profiles of electron and ion concentrations showed a more complicate behavior—a fast rise to a maximum followed by a gradual decay. The maximum ion concentrations were much higher and electron concentrations were much lower than in similar conditions in argon. The extent of the subsequent decay of electron concentration increased proportionally to the square of the C₃O₂ concentration. In the mixture with 2% C₃O₂ the final electron concentration was about 100 times less than in pure argon. The characteristic decay time of free charges varied from 400 to 40 μs and decreased proportionally to the square root of the charge concentration. The data analysis is based on the assumption that the observed redistribution of electron and ion concentrations is caused by charging of the carbon particles formed during pyrolysis of C₃O₂. The kinetics of particle charging and the final distribution of charges were evaluated by the analysis of electron and ion fluxes to the particles in accordance with the electric potentials of charged particles and corresponding sodium ionization. A predominance of negatively charged particles, caused by the high electron mobility, resulted in their much higher concentration than the concentration of free electrons.     

弱电离尘埃等离子体的介电张量研究

忽略磁场作用,通过求解含BGK碰撞项的Boltzmann方程和尘埃粒子充电方程导出了弱电离尘埃等离子体介电张量的表达式.证明了“冷”尘埃等离子体的纵向介电张量系数与横向介电张量系数相等.完善了弱电离尘埃等离子体电磁特性的理论模型. 关键词： 弱电离尘埃等离子体 Boltzmann方程 充电方程 介电张量     

Charging dynamics of polymer due to electron irradiation: A simultaneous scattering-transport model and preliminary results

We present a novel numerical model and simulate preliminarily the charging process of polymer subjected to electron irradiation of several 10 keV. The model includes the simultaneous processes of electron scattering and ambipolar transport and the influence of a self-consistent electric field on the scattering distribution of electrons. The dynamic spatial distribution of charges is obtained and validated by existing experimental data. Our simulations show that excess negative charges are concentrated near the edge of the electron range. However, the formed region of high charge density may extend to the surface and bottom of a kapton sample, due to the effects of electric field on electron scattering and charge transport, respectively. Charge trapping is then demonstrated to significantly influence the charge motion. The charge distribution can be extended to the bottom as the trap density decreases. Charge accumulation is therefore balanced by the appearance and increase of leakage current. Accordingly, our model and numerical simulation provide a comprehensive insight into the charging dynamics of polymer irradiated by electrons in the complex space environment.     

Experimental thermal performance study of natural graphite as sensible heat storage material using different heat transfer fluids

In this paper thermal performance of graphite-based sensible heat storage system with embedded helical coil in rectangular shell was studied. Plain water at four flow rates (0.25 LPM–1.0 LPM) and four inlet temperatures (60°C–90°C) was passed through the graphite bed and charging time was measured. Expanded graphite/water suspension and Al₂O₃/water nanofluid were also used to study charging behavior of graphite. Results showed that charging time of packed bed was reduced with increase in flow rate and inlet temperature of heat transfer fluid. Charging time using expanded graphite/water solution and nanofluid was 14.2% and 21.2% lesser than water.

Abbreviations: h_i: internal heat transfer coefficient (W m^?2 K^?1); HTF: Heat transfer fluid; h_o: External heat transfer coefficient (W m^?2 K^?1); LPM: liter per minute; k: thermal conductivity (W m^?1 K^?1); TSU: Thermal storage unit     

一种新的航天器外露介质充电模型

为综合考虑高能电子辐射与周围等离子体对航天器外露介质充电的影响,在航天器内带电模型的基础上,通过添加边界充电电流来考虑等离子体与航天器介质表面的相互作用,并统一参考电位为等离子体零电位,建立了航天器外露介质充电模型,给出了新模型的一维稳态解法,并与表面充电模型和深层充电模型进行了对比分析.结果表明:新建模型能够综合考虑表面入射电流、深层沉积电流和传导电流对充电的耦合作用过程,实现外露介质表面和深层耦合充电计算,有利于全面评估航天器外露介质的充电问题.     

电动汽车充电站监控系统设计

针对电动汽车日渐普及这一情况,本论文设计了一套电动汽车充电站监控系统。首先,给出了监控系统总体结构;其次,选择了系统的通信方式,并给出详细的 CANET转换器配置和通讯编程实现;然后,基于Microsoft Visual Studio平台,利用C#开发了充电站上位机监控系统,该系统可实时监控充电桩及其配电系统的运行情况,保证了电动汽车充电站的安全运行。     

双麦克斯韦分布尘埃等离子体中尘埃粒子的充电研究

根据充电方程和电荷守恒条件,导出了双麦克斯韦分布的弱电离尘埃等离子体充电频率(电荷弛豫速率),给出了充电电流的计算公式. 对结果分析表明,定向运动速度大小对充电电流和充电频率有一定的影响,充电频率随着定向速度增加而减小,当定向速度远远小于电子的热速度时,充电频率与文献给出的表达式一致. 关键词： 尘埃等离子体 双麦克斯韦分布 充电频率     

高能电子辐射下聚四氟乙烯深层充电特性

介质深层充放电现象是诱发航天器异常故障的重要因素之一.分析了高能电子辐射下介质内部电荷沉积、能量沉积特性和电导特性,考虑了真空与介质界面电荷对电场分布的影响,建立了介质二维深层充电的物理模型,并基于有限元方法实现了数值计算.计算了高能电子辐射下聚四氟乙烯的深层充电特性.结果表明:真空环境下,介质的表面存在较弱的反向电场,随着介质深度增大,电场减小至零,随后逐渐增大,最大值出现在靠近接地附近,但在接地点,电场存在小幅降低.分析了不同辐射时间下(1 h,1 d,10 d和30 d),介质内部最大电位和最大电场的时空演变特性.随着辐射时间的增加,最大电位由-128V增加至-7.9×104V,最大电场由2.83×105V·m-1增加至1.76×108V·m-1.讨论了入射电子束流密度对最大电场的影响,典型空间电子环境(1×10-10A·m-2)下,电子辐照10 d时,介质内部最大电场为2.95×106V·m-1.而恶劣空间电子环境(2×10-8A·m-2)下,电子辐射42 h,介质内部最大电场即达到108V·m-1,超过材料击穿阈值(约为108V·m-1),极易发生放电现象.该物理模型和数值方法可以作为航天器复杂部件多维电场仿真的研究基础.     

Low-frequency variable charge solitary waves in a collisionless dusty plasma with a Cairns-Gurevich ion velocity distribution

In this paper, the problem of large amplitude dust acoustic (DA) solitons has been addressed in a charge varying dusty plasma with ions following a Cairns-Gurevich distribution. Based on the orbit motion limited approach, the correct Cairns-Gurevich ion charging current is presented for the first time. The expression relating the variable dust charge to the plasma potential is given in terms of the Lambert function and we take advantage of this transcendental function to, carefully, analyse DA solitons in a charge varying dusty plasma with trapped nonthermal ions. Our results show that the spatial patterns of the variable charge solitary wave are significantly changed due to the presence of ion population modelled by the Cairns-Gurevich distribution. An addition of a small concentration of trapped nonthermal ions makes the solitary structure less spiky, grows the net negative charge residing on the dust grain surface, and contributes to the electron depletion. Finally, our investigation is extended to highlight the effect of the grain dust charge variation. We have shown that under certain conditions, the impact of dust charge fluctuation may furnish an alternate physical mechanism rasing anomalous dissipation, which becomes more strong and may predominate over the dispersion as the nonthermal character of ions following the Cairns-Gurevich distribution increases.