低轨道卫星表面充电模拟

卫星在太空运行过程中,在周围等离子体和光电效应等综合作用下,会带上与周围等离子体环境不同的悬浮电位,这个电位会影响星上测量载荷的测量精度和测量范围。利用航天器与等离子体相互作用系统软件SPIS,采用粒子分室法模拟了低轨道(710km)卫星的充电特性。结果表明,由于等离子体温度低、浓度高,卫星的充电电位较低(-0.719V);而周围的等离子体环境受卫星尾迹效应的影响显著。     

低轨道卫星表面充电模拟

卫星在太空运行过程中,在周围等离子体和光电效应等综合作用下,会带上与周围等离子体环境不同的悬浮电位,这个电位会影响星上测量载荷的测量精度和测量范围.利用航天器与等离子体相互作用系统软件SPIS,采用粒子分室法模拟了低轨道(710 km)卫星的充电特性.结果表明,由于等离子体温度低、浓度高,卫星的充电电位较低(-0.719 V);而周围的等离子体环境受卫星尾迹效应的影响显著.     

低轨道卫星表面充电模拟

卫星在太空运行过程中，在周围等离子体和光电效应等综合作用下，会带上与周围等离子体环境不同的悬浮电位，这个电位会影响星上测量载荷的测量精度和测量范围。利用航天器与等离子体相互作用系统软件SPIS，采用粒子分室法模拟了低轨道（710km）卫星的充电特性。结果表明，由于等离子体温度低、浓度高，卫星的充电电位较低（-0.719V）；而周围的等离子体环境受卫星尾迹效应的影响显著。     

用于离子激光器的容性耦合射频放电理论研究

为了对高电流下的容性耦合射频(CCRF)放电有清晰的了解,我们建立了CCRF放电的自洽模型,研究了CCRF放电的放电特性和从低电流向高电流模式的转变规律.利用两电子组模型,结合流体模型自洽地研究了射频放电中放电参量与射频电压之间的变化关系.研究表明,在不考虑电极的γ过程时,射频放电的参量基本上随射频电压线性变化,没有出现转变迹像,而当考虑电极的γ过程后,射频放电明显出现两个不同的运行区域,对应于射频放电的低电流α区和高电流γ区.当射频放电出现转变后,传导电流密度和等离子体密度大幅度升高,鞘层电场增强,鞘层宽度明显减小,等离子体电场也减小.在γ放电下,快电子的电离速率分布主要在放电中心区且比较均匀,说明快电子在电极鞘层间形成了振荡,因此放电类似于空心阴极放电.(PC11)     

强激光驱动的运动电场加速质子的研究

为了研究激光辐射压驱动的运动电场中加速质子的相关问题,对强激光与等离子体相互作用过程进行了理论分析,并采用2维粒子模拟方法,对理论分析结果进行了数值模拟验证。结果表明,当超短超强激光脉冲与处在背景等离子体前方的薄固体平靶相互作用时,在固体靶后部形成一个由电子层-离子层组成的双层结构,在激光辐射压的不断推进下,双层结构在背景等离子体里以一定速度传播形成一个运动电场;在背景等离子体中的质子被这个运动电场捕获并能加速到很高的能量,质子的最大能量达到20GeV。理论分析结果与2维粒子模拟结果符合得很好。     

AlGaN/GaN HEMT中电场分布的ATLAS模拟

用Silvaco的ATLAS软件模拟了栅场板参数对AlGaN/GaN HEMT中电场分布的影响.模拟结果表明,场板的加入改变了器件中电势的分布情况,降低了栅边缘处的电场峰值,改善了器件的击穿特性;场板长度(LFP,length of field plate)、场板与势垒层间的介质层厚度t等对电场的分布影响很大.随着LFP的增大、t的减小,栅边缘处的电场峰值Epeak1明显下降,对提高器件的耐压非常有利.通过对相同器件结构处于不同漏压下的情况进行模拟,发现当器件处于高压下时,场板的分压作用更加明显,说明场板结构更适合于制备用作电力开关器件的高击穿电压AlGaN/GaN HEMT.     

双层等离子体对6 GHz高功率微波防护实验

针对高功率微波对电子设备的安全威胁,设计了一种双层柱状等离子体阵列对高功率微波进行防护。其中单根等离子体柱的直径为25.4 mm,长度为600 mm,等离子体频率与碰撞频率可进行控制。利用搭建的实验测量系统,研究了微波极化方向、等离子体电子密度、放电单元层数等因素对高功率微波透射衰减的影响。实验结果表明:当高功率微波未激发等离子体产生非线性效应时,TM极化时的防护效果优于TE极化时的防护效果,且能量衰减分别可达20.9 dB和14.7 dB;随等离子体电子密度增大,微波透射功率减小,防护效果增强;由于层间反射作用,双层等离子体对高功率微波的透射衰减远大于单层等离子体衰减值的两倍。     

测量材料吸收毫米波性能的新型探头

提出了用于测量吸波材料吸收雷达波性能的新型探头。引入高次模,采用相位分析法,克服了多变量干扰,简化计算。在固定区间求偏差和方差最小值,得到平缓电场。仿真结果证明新型探头口径电场平缓,波动小,近似平面波。新型探头的平面波范围与口径比为53%,比现有厘米波探头扩大了17.2%,能精确地模拟雷达对材料的辐射,减小测量误差。此探头尺寸较小,可广泛应用于户外测量材料吸收毫米波雷达电磁波的性能。     

相对运动等离子体平板与电磁波相互作用研究

高超声速飞行器在飞行过程中,由于高温高压的作用,会在飞行器表面形成一层等离子体鞘层,飞行器及其等离子体鞘层相对于地面测控中心做高速相对运动,对目标物电磁回波会带来严重影响.此外,等离子体鞘层的时变特性,也会对目标物雷达回波进行调制,使测控中心难以识别、跟踪目标.本文利用Lorentz-FDTD方法研究了相对运动等离子体鞘层与电磁波之间的相互作用,并分析了等离子体鞘层的相对运动特性和时变特性对电磁波造成的影响,发现运动的时变等离子体除了对电磁波造成多普勒频移外,还会对入射波频谱进行调制.     

准分布式光纤表面等离子体波传感器

研究了一种基于波分复用原理的准分布式光纤表面等离子体波传感器。应用光波导理论和多层膜反射理论分析了表面等离子体波效应在同一光纤探头中连续被激励的原理及其传感模型。通过数值模拟和相应实验分别考察了蒸镀调制层对表面等离子体波共振(SPR)效果的影响,并在此基础上给出了设计的一般步骤和原则。实验结果表明,蒸镀不同厚度的Ta2O5薄膜将导致表面等离子体波共振光谱发生偏移,且随着膜厚增加而逐渐发生红移;当液体折射率n0处于1.333~1.388之间时,蒸镀有Ta2O5薄膜的光纤表面等离子体波传感器波长灵敏度达到2235 nm/RIU(Refractive Index Unit);通过在一支光纤探头上依次加工两个表面等离子体波传感区域,实现了对光波信号的连续调制。     

Recombination effects with high-pressure Langmuir probes

With increasing ion density, the ion current collected by a negatively biased electric probe is eventually dominated by ions produced by reactive processes in the vicinity of the probe. Here, we derive an expression for the probe current to a cylindrical probe when all the ions collected to the probe are assumed to be generated within the sheath which surrounds the probe. Measurements of probe current in a seeded atmospheric-pressure flame are in good agreement with the theory. The significance of reaction processes is reinforced by the fact that the maximum probe current is found to be approximately three times the total current that the flame would produce with frozen chemistry, i.e. the saturation current.     

The influence of the measurement probe on the evaluation of electromagnetic fields

In this paper, the influence of the measurement probe on the evaluation of the far and near field of an electromagnetic source is characterized. While measuring, the electromagnetic field will be disturbed by the measurement probes themselves. Therefore, not the true, free-space field but the disturbed field will be measured. The disturbance can not be fully taken into account by the calibration, especially in the near field. It is found that in the near field, these disturbances are much higher than in the far field for a large sensitive measurement probe. This paper will show that when the disturbance must be limited to a predefined value (e.g., 5%), a suitable measurement probe with maximum sensitivity can be selected. The characterization was performed using a numerical electromagnetic computational program.     

张衡一号卫星观测的地基VLF波电离层加热扰动特征

电离层扰动主要由太阳活动和地球表面活动引起,通过对已知地基甚低频（very low frequency, VLF）波发射源引发的等离子体扰动进行特征研究,对于认识电离层环境变化具有重要的参考意义. 文中主要介绍了张衡一号01卫星原位探测科学载荷等离子体分析仪（plasma analyzer package, PAP）观测系统和数据产出,对该载荷在507 km轨道原位观测的、由地基NWC站大功率VLF人工源辐射引起的电离层加热扰动现象及特征进行了总结和分析. 观测结果表明:氧离子密度、离子温度、离子漂移速度等多个原位观测量在夜侧轨道均同时记录到NWC站上空北侧约50～500 km区域出现的电离层加热扰动现象,扰动持续范围约为300～400 km;通过对相同轨道电场数据进行功率谱计算可知,该区域电场增强主要频率与NWC站发射频率相同. 上述观测结果验证了张衡一号01卫星PAP对电离层离子参量扰动现象具有一定的探测分辨能力,地基大功率VLF电波能够对电离层等离子体环境产生明显的扰动影响,且扰动区域相对于发射源位置向磁赤道方向发生偏移.     

GMM-FBG光纤电流传感器温度补偿研究

为解决因超磁致伸缩材料(GMM)磁致伸缩系数 对温度敏感而影响GMM-FBG光纤电流传 感器响应准确度的问题,研究了温度补偿的方法,构建了GMM磁场与温度的多场耦合模型, 进行温度传感实验、电流的通断实验、及不同磁场方向上的电流响应实验,设计了十字形传 感探头,利用垂直磁场方向的GMM的磁场不敏感性进行电流传感器的温度补偿,提高了GMM- F BG光纤电流传感器响应准确度。结果表明:垂直于磁场方向上的传感器中心波长值变化量为 ±0.05 pm,可忽略磁场的影响,温补后的拟合曲线与通断实验的拟 合曲线残差平方和为0.011,几乎完全重合, 可消除温度对GMM-FBG电流传感器的影响,使电流测量更加精确,并实 现电流与温度的同时测量,可满足当代电力系统的应用需求。     

Langmuir-probe measurement of ionisation density on a plasma jet

The current to a negative probe in an argon plasma jet shows a strong dependence on probe bias and is up to an order of magnitude less than the usual convection/diffusion saturation current. The current is also in surprisingly good agreement with the calculated sheath/convection current. The results are attributed to electron?ion recombination in the vicinity of the probe.     

空间等离子体鞘层的时域特性研究

空间等离子体环境,是计算机及各类电子设备所面临的新型恶劣环境。通过将设备表面简化为平面,给出了一维粒子层模型。根据静电场理论给出了描述鞘层电位的Poisson方程、等离子体理论和Boltzmann方程,给出了粒子数密度守恒方程。通过牛顿运动定律建立了等离子体的动量方程。基于Poisson方程、粒子数密度守恒方程和等离子体动量方程建立了等离子体鞘层动力学模型。该模型可以给出航天器表面附近等离子体鞘层形成过程的时域特性,如电荷通量、充电电位随时间的变化规律,为电子设备抗空间等离子体防护技术的研究提供理论基础。     

A voltage calibration technique of electro-optic probing for characterization internal to IC’s chip

This paper simulates the electric potential distribution and the electro-optic (EO) signal amplitude in a longitudinal poled EO polymer external probe tip on the electric signal transmission lines under test. The influence of the circuit layout on the EO probing is discussed. A novel probing configuration with a poled polymer EO probe tip is built and demonstrated for the first time, by which the signal voltage level corresponding to the EO signal can be calibrated. Using the new probe tip, we examine the influence of the variations of the linewidth and the spacing between neighboring lines on the EO signal. The results indicate that when the vertical distance between the tested point on the lines and the reference electrode is not larger than that between the tested point and its neighboring conductor, the disturbance from circuit layout can be avoided so that the voltage calibration of EO signal can be carried out.     

Radiation from an aperture in a conducting cylinder coated with a moving plasma sheath

The electromagnetic radiation from an aperture on a conducting cylinder coated with a moving isotropic plasma sheath is considered. Numerical results are presented to illustrate the radiation patterns as functions of sheath velocity and plasma frequency for the circumferential slot and axial slot apertures. It is found for the circumferential slot aperture that the radiation is enhanced in the direction of sheath motion when the plasma is overdense and that relatively little change occurs when the sheath is underdense. For the axial slot, it is found that an electromagnetic field is radiated whose polarization is normal to that of the field radiated under stationary conditions, in addition to a field of the usual polarization. Significant alterations of radiation patterns from their form when the sheath is stationary can occur at relatively small velocities if the wave frequency is near the plasma frequency.     

海底光纤复合电缆金属护套光单元感应电势计算

运行中交变电场在海底光纤复合电缆的光单元金属护套上会产生感应电势,感应电势的大小是决定海底光纤复合电缆内采用何种光单元结构的一个主要因素。给出了金属护套光单元感应电势的计算公式,并举例计算了感应电势及感应电流。计算结果表明,一般长度的海底光纤复合电缆中金属护套光单元的感应电势较小,在安全范围内;具有径向和纵向阻水的普通金属护套光单元可用于海底光纤复合电缆中,不需要采取特殊措施。     

Radiation from a gyro-plasma sheathed aperature

It is shown that the presence of a gyrotropic plasma sheath covering a rectangular slot radiator may not alter significantly the radiation pattern when the static magnetic field is perpendicular to the slot. The plasma covered antenna remains omnidirectional and the radiated power is not significantly reduced when the cyclotron frequencyomega_{b}, the collision frequencynu, and the operating frequencyomega, fulfill the inequalityomega_{b}^{2}ggomega^{2}+nu^{2}. It is also found that the matching between the plasma covered antenna and its surrounding is sharply improved for certain combinations of the plasma sheath parameters and the operating frequency. This finding may have an application in plasma diagnostics, the slab widthLand the plasma frequencyomega_{p}can be determined by varyingomega_{i}andomegaaccording to an expression derived in this paper.