Distribution of electric current in solar plasma loops

The distributing profile of electric current in solar plasma loop is a key factor for the MHD instabilities of the loops. However, it is very difficult to measure such profile in single loop. In this paper, we assume that, in spite of the complexity of the structure in most of the sunspots, the distribution of the electric current in some small simple sunspots may reflect the main feature of the distribution in solar plasma loops. We utilize the high-cadence, high-resolution vector magnetograms observed by Big Bear Solar Observatory (BBSO) to derive the longitudinal electric current and analyze the distribution of the longitudinal electric current in the region of sunspots, and simulate the distributing features of the solar plasma loops. From these analysis, we find that the electric current in some small simple sunspots, or to say in plasma loops, are concentrated to their center. Such distribution feature is consistent with the theory of pinch effect in current-carrying plasma loops.     

Cathode design investigation based on iterative correction of predicted profile errors in electrochemical machining of compressor blades

Electrochemical machining (ECM) is an effective and economical manufacturing method for machining hard-to-cut metal materials that are often used in the aerospace field. Cathode design is very complicated in ECM and is a core problem influencing machining accuracy, especially for complex profiles such as compressor blades in aero engines. A new cathode design method based on iterative correction of predicted profile errors in blade ECM is proposed in this paper. A math-ematical model is first built according to the ECM shaping law, and a simulation is then carried out using ANSYS software. A dynamic forming process is obtained and machining gap distributions at different stages are analyzed. Additionally, the simulation deviation between the prediction profile and model is improved by the new method through correcting the initial cathode profile. Further-more, validation experiments are conducted using cathodes designed before and after the simulation correction. Machining accuracy for the optimal cathode is improved markedly compared with that for the initial cathode. The experimental results illustrate the suitability of the new method and that it can also be applied to other complex engine components such as diffusers.     

Substorm activity during the main phase of magnetic storms induced by the CIR and ICME events

In this work, the relation of high-latitude indices of geomagnetic activity (AE, Kp) with the rate of storm development and a solar wind electric field during the main phase of magnetic storm induced by the CIR and ICME events is investigated. 72 magnetic storms induced by CIR and ICME events have been selected. It is shown that for the CIR and ICME events the increase of average value of the Kp index (Kp_aver) is observed with the growth of rate of storm development. The value of Kp_aver index correlates with the magnitude of minimum value of Dst index (|Dst_min|) only for the ICME events. The analysis of average values of AE and Kp indices during the main phase of magnetic storm depending on the SW electric field has shown that for the CIR events, unlike the ICME events, the value of AE_aver increases with the growth of average value of the electric field (Esw_aver). The value of Kp_aver correlates with the Esw_aver only for the ICME events. The relation between geomagnetic indices and the maximum value of SW electric field (Esw_max) is weak. However, for the ICME events Kp_aver correlates with Esw_max.     

磁层电场仪前端信号处理电路研究

针对磁层稀薄等离子体环境中的电场测量,设计了一种电场仪前端信号处理电路方案.双探针电场仪通过向等离子体输出驱动电流,测量两探针间的电位差,从而测量空间电场的探测仪器.在磁层稀薄等离子体环境下,等离子体阻抗较高,电场仪探针将工作在较高的工作电压上.若探针电压接近或超过电路耐压值,则可能会影响探测结果,甚至损坏电场仪.本文结合低偏置电流的电压跟随方案和反馈悬浮电源控制方案,解决了稀薄等离子体环境中电场测量的弱电流采样和高动态电位处理问题,并采用低噪声元件和特殊电路设计,控制电路噪声.测试结果显示,本方案可使探针适应±100V的悬浮电位,实现150kHz带宽的电场信号测量,且噪声小于14nV·mHz-1/2,满足目前空间电场仪测量精度需求.      

一种基于石墨烯的脉冲星导航X射线探测器

针对脉冲星导航要求X射线探测器具有高能量分辨率和高时间分辨率的需求,研究基于石墨烯电场效应来实现X射线探测的可行性。通过蒙特卡罗方法模拟不同能量X射线和不同厚度探测器基底的相互作用过程,得到不同厚度探测器对X射线的探测效率。利用有限元方法分析X射线在探测器内电离产生载流子的输运过程,验证了X射线入射对石墨烯电学特性的影响。理论分析计算探测器的时间分辨率和能量分辨率等指标参数,结果表明：基于石墨烯电场效应的X射线探测器具有较高的能量分辨率和时间分辨率,是一种潜力巨大的X射线探测方式,可满足未来脉冲星导航的工程应用。     

电动帆航天器谷神星探测任务轨迹优化

针对电动帆航天器谷神星探测任务轨迹优化问题,提出一种基于高斯伪谱法和遗传算法的混合优化算法。为了验证所提出的混合优化算法有效性,并考察任务起始时间和电动帆特征加速度对探测任务的影响,进行了一定数量的数值仿真。仿真结果表明：电动帆航天器自地球至谷神星的飞行时间随着起始时间的变化呈周期性波动,波动周期基本与地球和谷神星的会合周期一致;电动帆航天器的特征加速度越小,完成过渡所需要的飞行时间越长,且一个具有中等特征加速度的电动帆航天器便能在可接受的时间内完成自地球至谷神星的过渡;所提出的混合优化算法是有效的,能够在无任何初值猜测的情况下完成电动帆航天器飞行轨迹的优化。     

A strong robustness open-circuit fault diagnosis strategy for novel fault-tolerant electric drive system based on d-q-axis current signal

To diagnose the Open-Circuit (OC) fault in the novel fault-tolerant electric drive system, based on d-q-axis current signal, a strong robustness diagnosis strategy is proposed and investigated. Fewer independent power supplies and converters are required in the novel fault-tolerant electric drive system based on Dual-Winding Permanent Magnet Motor (DWPMM), and the system’s reliability, usage ratio and power density have been improved compared to the conventional fault-tolerant motor drive system. However, the novel fault-tolerant electric drive system has the OC fault diagnostic false alarms issue when load changes suddenly or under light-load condition. And it lacks the research on the diagnostic method when the system encounters intermittent OC fault in power switches. By theory derivation, simulation and experimental verification, it can be concluded that the proposed strong robustness OC fault diagnosis strategy based on d-q-axis current signal can overcome the OC fault diagnostic false alarms issue when load changes suddenly or under light-load condition. And it can detect and locate the OC fault of single-phase winding in real time, and diagnose the intermittent OC fault of power switches.     

Electric sail,photonic sail and deorbiting applications of the freely guided photonic blade

We consider a freely guided photonic blade (FGPB) which is a centrifugally stretched sheet of photonic sail membrane that can be tilted by changing the centre of mass or by other means. The FGPB can be installed at the tip of each main tether of an electric solar wind sail (E-sail) so that one can actively manage the tethers to avoid their mutual collisions and to modify the spin rate of the sail if needed. This enables a more scalable and modular E-sail than the baseline approach where auxiliary tethers are used for collision avoidance. For purely photonic sail applications one can remove the tethers and increase the size of the blades to obtain a novel variant of the heliogyro that can have a significantly higher packing density than the traditional heliogyro. For satellite deorbiting in low Earth orbit (LEO) conditions, analogous designs exist where the E-sail effect is replaced by the negative polarity plasma brake effect and the photonic pressure by atmospheric drag. We conclude that the FGPB appears to be an enabling technique for diverse applications. We also outline a way of demonstrating it on ground and in LEO at low cost.     

喷雾电火花加工稳定性

针对现有雾中电火花加工过程中放电过程稳定性不足的问题,采用去离子水超声雾化及工件端施加辅助超声振动的方式以提高加工过程的稳定性。分别以自来水及纯水产生的雾介质为工作介质进行电火花加工对比实验,结果表明:以超声雾化方式获得的微细雾介质,可有效降低短路率。同时还进行了侧向喷雾加工试验,发现通过侧向喷雾,可以进一步提高加工过程的稳定性,获得更好的加工效果。     

电网时间同步技术标准制定

电网时间同步系统对电力工业非常重要,制定电网时间同步技术标准也很重要。介绍了国家电力公司华东公司的企业标准《华东电网时间同步系统技术规范》的制定过程和主要内容,并对编制中问题及其改进加以讨论,指出制定标准货柜繁殖是电力时间同步网建设的第一步,需要各方面的协作努力,尤其是管理、培训等“软件”工作跟上去,才能使电网的时钟等“硬件”设备充分发挥作用。