减压直流等离子体射流电子温度的双静电探针测量

建立了一套双静电探针诊断系统,用于检测在气流量为4.2 slm、弧电流为80 A、真空室压力为165Pa的条件下纯氩直流非转移弧等离子体射流的电子温度及其分布。结果表明:发生器出口处射流中心的电子温度约为14 500 K,射流中电子温度随离开发生器出口的轴向或径向距离的增加而单调降低;径向电子温度梯度约为263 K/mm,轴向电子温度梯度为69 K/mm;射流中电子温度随弧电流增加而单调上升。     

不同稀释气体下等离子体辅助甲烷点火

等离子体由于可以同时在燃料反应中增加化学效应与热效应,有望成为辅助点火的有效技术途径。构建了基于激波管的等离子体辅助甲烷点火实验系统,测量了甲烷自点火、持续放电以及放电后断电条件下的点火延迟时间,分析了不同稀释气体下等离子体对甲烷点火延迟的缩短效果。构建了等离子体发射光谱测量系统,测量了放电单元中的发射光谱。在实验条件下,点火温度越高,持续放电下活性粒子的浓度越高。较小的放电功率(4 W)即可将甲烷的点火延迟时间缩短30%~95%。稀释气体为Ar时,等离子体在点火温度小于1 000 K或大于1 400 K时对甲烷点火延迟时间缩短作用更好。稀释气体为N2时,随着点火温度的升高,等离子体对甲烷点火延迟时间作用效果随之降低。     

Real-time GLE alert in the ANMODAP Center for December 13, 2006

Within the last years, a real-time system to monitor high energy cosmic rays for space weather use has been operated at Athens cosmic ray station. Neutron monitors and satellite high resolution data in real time are used, making it possible to observe cosmic rays in dual energy range observations. In large solar energetic particle (SEP) events, ground level enhancement (GLE) can provide the earliest alert for the onset of the SEP event. This system watches for count rate increases recorded in real time by 23 neutron monitors, which triggers an alarm if a ground level enhancement (GLE) of cosmic ray intensity is detected.     

Effects of space weather on the ionosphere and LEO satellites’ orbital trajectory in equatorial,low and middle latitude

We study the effects of space weather on the ionosphere and low Earth orbit (LEO) satellites’ orbital trajectory in equatorial, low- and mid-latitude (EQL, LLT and MLT) regions during (and around) the notable storms of October/November, 2003. We briefly review space weather effects on the thermosphere and ionosphere to demonstrate that such effects are also latitude-dependent and well established. Following the review we simulate the trend in variation of satellite’s orbital radius (r), mean height (h) and orbit decay rate (ODR) during 15 October–14 November 2003 in EQL, LLT and MLT. Nominal atmospheric drag on LEO satellite is usually enhanced by space weather or solar-induced variations in thermospheric temperature and density profile. To separate nominal orbit decay from solar-induced accelerated orbit decay, we compute $r\text{,}h$ and ODR in three regimes viz. (i) excluding solar indices (or effect), where $r=r_0\text{,}h=h_0$ and $\mathit{ODR}={\mathit{ODR}}_0$ (ii) with mean value of solar indices for the interval, where $r=r_m\text{,}h=h_m$ and $\mathit{ODR}={\mathit{ODR}}_m$ and (iii) with actual daily values of solar indices for the interval ($r\text{,}h$ and ODR). For a typical LEO satellite at h?=?450?km, we show that the total decay in r during the period is about 4.20?km, 3.90?km and 3.20?km in EQL, LLT and MLT respectively; the respective nominal decay ($r_0$) is 0.40?km, 0.34?km and 0.22?km, while solar-induced orbital decay ($r_m$) is about 3.80?km, 3.55?km and 2.95?km. h also varied in like manner. The respective nominal ${\mathit{ODR}}_0$ is about 13.5?m/day, 11.2?m/day and 7.2?m/day, while solar-induced ${\mathit{ODR}}_m$ is about 124.3?m/day, 116.9?m/day and 97.3?m/day. We also show that severe geomagnetic storms can increase ODR by up to 117% (from daily mean value). However, the extent of space weather effects on LEO Satellite’s trajectory significantly depends on the ballistic co-efficient and orbit of the satellite, and phase of solar cycles, intensity and duration of driving (or influencing) solar event.     

等离子体气动激励体积力的实验研究

等离子体流动控制作为一种新概念主动流动控制技术,其物理作用依据之一是"动力效应".体积力作为表征"动力效应"的重要参数,对研究等离子体流动控制的原理具有重要意义.介绍了实验原理及系统的基本组成,对等离子体气动激励体积力进行了实验测量.结果表明:体积力的大小在mN量级;固定激励频率,激励电压增大时,体积力增大,且线性关系非常明显;固定激励电压,体积力受激励频率的影响不大.     

TiAl合金表面激光重熔陶瓷涂层组织及耐磨性能

为了提高TiAl合金耐磨性能,采用等离子喷涂和激光重熔复合工艺在TiAl合金表面制备了Al2O2-13% TiO2(质量分数)复合陶瓷涂层.用扫描电镜(SEM)和显微硬度计分析了涂层微观结构和显微硬度,同时对涂层的磨损特性进行了考察.结果表明,经过激光重熔处理后,陶瓷涂层颗粒细化,片层状组织得以消失,致密性提高,获得了基本没有裂纹等缺陷的重熔层.由于陶瓷材料导热系数较低的影响,激光重熔时无法使整个陶瓷层实现重熔,重熔后的陶瓷涂层形成了晶粒细小的等轴晶重熔区、烧结区以及片层状残余等离子喷涂区.激光重熔处理后涂层的显微硬度明显提高,其耐磨性能也明显优于原等离子喷涂层.     

等离子体气动激励的诱导气流速度的实验研究(英文)

等离子体流动控制是基于等离子体气动激励的主动流动控制,可用于改善飞行器和动力装置空气动力特性.为了探索等离子体流动控制的内在机理,在不同的参数条件下,对等离子体气动激励的诱导气流速度进行了实验研究.实验结果表明:等离子体气动激励可以把激励器表面空气加速到每秒几米的速度,诱导气流与激励器表面有一个约5°的夹角,且气流经加速后会形成漩涡结构.固定激励频率,诱导气流速度随激励电压增大而增大;固定激励电压,诱导气流速度受激励频率的影响不大;激励器布局对等离子体气动激励器的性能有重要影响.     

等离子体覆盖目标散射特性的RKETD-FDTD分析

采用一种既保证计算的高效率,又有较高的计算精度的龙格库塔指数时程差分时域有限差分法(RKETD-FDTD)研究了等离子体的散射特性.该算法解决了电磁波在色散介质中传播的计算问题,导出了在等离子体介质中RKETD-FDTD迭代公式.文中分别计算了等离子体平板的反射系数和非均匀等离子体覆盖导体柱的散射特性,所得结果与解析结果相符合,并且表明等离子体涂层选择合适的碰撞频率,能有效地减小目标的雷达散射截面(RCS).     

ICP中放电模式转化过程中悬浮电位变化的多样性

研究了射频感性耦和等离子体(ICP)中悬浮电位在模式转化过程(E-H模式)的变化多样性。实验研究了射频功率在5W-1000W,气压在2Pa-50Pa的范围内,通过改变导电地面积、匹配网络、气压等参数,使用Z-Scan系统、电流电压探头以及静电探针进行测量的等离子体悬浮电位在模式转化过程中随功率变化的多种形式,同时给出了r型射频匹配网络的正负反馈区的区别,并对产生的多种现象进行了的理论解释。     

一种用于快速跟踪视线的空间拦截器姿态控制方法

以空间拦截器的纵轴在中、末制导段要求指向目标的视线，按最小空间角距旋转，作为跟踪目标的姿态定向的假想坐标系，形成本体坐标系相对假想坐标系的误差四元数。由拦截器的转动角速度分量与误差四元数作为状态反馈构造稳态姿态控制的数学模型。为了得到姿态控制所需的变控制力矩，运用PWPF调制器对常值推力姿控发动机的稳态和脉冲工作状态进行调制，构造所谓的“数字变力矩”控制器，实现对姿态的连续控制。仿真计算结果表明，该方法是实际可行的。