航天器介质放电脉冲频谱特征实验研究

空间电子辐射环境下,航天器介质的充放电效应是威胁航天器安全的重要因素.介质放电现象除与材料参数及构型相关外,还与空间电子环境密切相关.本文通过电子枪和Sr90放射源在地面实验装置上模拟空间电子辐照环境,测试了环氧树脂、聚四氟乙烯、聚酰亚胺等常见空间材料在不同温度、不同电子能量和电子束流强度影响下的放电脉冲,并对放电电流脉冲和电场脉冲进行频谱分析.实验分析结果表明,介质材料的放电电流脉冲频谱具有明显的单峰结构,该峰值与材料厚度和入射电子能量相关,但受材料温度和辐照束流强度影响不大.      

溅射靶对离子推力器的热辐射影响研究

为了研究真空环境设备内溅射靶温度升高后对30cm离子推力器的热辐射影响，采用有限元分析的方法，首先对真空舱内的离子推力器羽流分布进行了模拟，在获得羽流对溅射靶造成的温度变化后，进一步分析了溅射靶温度升高对离子推力器温度以及栅极热形变位移所造成的影响。仿真结果显示，推力器羽流可采用定向分子流模型进行描述，羽流在真空舱内的扩散过程中几乎没有能量损失；30cm离子推力器工作时真空舱内大部分区域的气体压强在2×10^-3~6×10^-3 Pa；在溅射靶影响下，推力器加速栅和屏栅中心温度分别为352℃和440℃，边缘温度分别为342℃和411℃，屏栅和加速栅的间距缩小量由无溅射靶影响时的0.560mm增加到0.585mm；试验结果显示，加速栅和屏栅边缘温度分别为364℃和385℃，与仿真结果的比对误差均为6%，溅射靶后部羽流气体的温度测试值高于计算值约50℃，误差主要由于模拟中忽略了羽流粒子的能量沉积效应。     

150kV逆变电源性能优化及其束源特性

为了进一步提高电子束流发生系统工作的可靠性和稳定性,提高电子束加工质量,采用AC-DC-AC-DC-AC-DC的拓扑电路、新型功率变压器、高压脉冲检测技术、优化的束流反馈控制与灯丝加热电流闭环反馈控制技术等,分别优化了高压加速电源、偏压电源与灯丝加热电源。将所研制逆变电源与150 k V/30 k W电子枪、真空系统等组成了一套电子束流发生系统,测试了该电子束流发生系统输出的高压、最大束流以及灯丝加热电流、偏压变化对束流输出的影响。试验结果表明:经过优化的逆变电源高压输出达到-150 k V,高压输出线性度较好,最大束流达到200 m A;高压、灯丝加热电流给定时,随着偏压降低,束流输出逐渐增大;高压、偏压给定时,随着灯丝加热电流增大,束流输出存在死区、线性增大区和恒流区。     

电子照射对硅漂移探测器性能的影响

由于高能电子辐射的长期照射,新一代太阳X射线探测器硅漂移传感器的探测性能可能发生变化.通过用电子放射源模拟空间电子对硅漂移探测器进行辐射照射试验,以测试电子照射对传感器能量分辨率、效率、信号幅度等性能的影响.试验结果表明,长期的电子照射造成硅漂移探测器面损伤和体损伤,使其漏电流增大,信号幅度减小,能量分辨率也受到照射的影响,而探测效率未发生变化.     

一种低能量远焦距电子枪技术

针对可移动非接触式月球表面电位探测器的电位无扰动测量单元对低能远焦电子束的需求，设计了低能远焦电子枪。以平板二极管电子枪为电子源，匹配两个静电聚焦透镜，将电子源引出的发散电子束聚焦为需要的形状，并加速至所需能量。优化电子枪的几何参数以及施加在电极上的电位，电子枪引出的电子束能量在5～500 eV内，并且具有良好的电子光路特性。电子束能量为5 eV时，初始半径r为5 mm，束腰至电子枪出口的距离p约为133 mm。随着能量增加，r逐渐减小至500 eV时的3 mm左右，p逐渐减小至105 mm。电子束经月球表面电场反射被电子收集平极接收，仿真数据和理论分析结果均表明，电子枪的工作距离为400～600 mm，平板接收的电子占发射电子比例在96%以上。电子枪结构质量仅408 g，满足探测器对电子枪的质量需求。     

Absorbed dose measurements on external surface of Kosmos-satellites with glass thermoluminescent detectors.

In this paper we present absorbed dose measurements with glass thermoluminescent detectors on external surface of satellites of Kosmos-serie flying in 1983-87. Experiments were performed with thermoluminescent aluminophosphate glasses of thicknesses 0.1, 0.3, 0.4, 0.5, and 1 mm. They were exposed in sets of total thickness between 5 and 20 mm, which were protected against sunlight with thin aluminized foils. In all missions, extremely high absorbed dose values were observed in the first layers of detectors, up to the thickness of 0.2 to 0.5 gcm-2. These experimental results confirm that, during flights at 250 to 400 km, doses on the surface of the satellites are very high, due to the low energy component of the proton and electron radiation.     

高速撞击梯度电势靶板产生等离子体诱发的放电

针对在轨运行航天器在空间等离子体环境和空间带电粒子活动下诱发航天器表面梯度电势存在的客观现实,航天器在空间碎片的撞击下会诱发表面带电或深层电介质带电的航天器放电。为了在实验室模拟航天器表面存在电势差的真实情况,采用对航天器外表面分割的方法,在分割的表面间预留不同间距且在2靶板间加装电阻的方法创造具有梯度电势的高电势2A12铝板作为靶板。利用自行构建的梯度电势靶板的充放电测试系统、超高速相机采集系统和二级轻气炮加载系统,开展高速撞击梯度电势2A12铝靶的实验室实验。实验中,弹丸以入射角度为60°（弹道与靶板平面的夹角）、撞击速度约为3 km/s的条件撞击间距分别为2、3、4和5 mm的2A12铝高电势靶板,利用电流探针和电压探针采集放电电流和放电电压。实验结果表明:放电产生的等离子体形成了高电势与低电势靶板间的放电通道,且在梯度电势靶板间距分别为2、3 mm时诱发了一次放电,放电电流随高低电势靶板间间距的增加而减小;在梯度电势靶板间距分别为4、5 mm时诱发了二次放电,放电电流随高低电势靶板间间距的增加变化不明显。      

Laboratory simulation of the injection of energetic electron beams into the ionosphere—Ignition of the beam plasma discharge

Experiments, which somewhat simulate the injection of monoenergetic (several keV) electron beams into the ionosphere, have been performed in the very large (17 m × 26 m) vacuum chamber at Johnson Space Center. Typical operating ranges were: Beam current, I (0–130 mA), beam energy, E (0.5–3 kV), magnetic field, (0.3–2 G), path length, L (10–20 m), and injection pitch angle, α(0–80°). Measurements were carried out in both steady state and pulsed modes. In steady state and for constant V, B, p, L, α, the beam plasma discharge (BPD) is abruptly ignited when the beam current is increased above a critical value; at currents below critical, the beam configuration appears grossly consistent with single particle behavior. If it is assumed that each of the experiment parameters can be varied independently, the critical current required for ignition obeys the empirical relationship at p < 2 × 10^?5 torr:

$\text{I}\textcolor{red}{}\text{E}{}^{\mathrm{3/2}}\text{B}{}^{\mathrm{<mtext>0.7</mtext><mtext>pL</mtext>}}$

The BPD is characterized by 1) a large increase in the plasma production rate manifested in corresponding increases in the 3914 Å light intensity and plasma density, 2) intense wave emissions in a broad band centered at the plasma frequency and a second band extending from a few kHz up to the electron cyclotron frequency, 3) scattering of the beam in velocity space and 4) radial expansion and pitch angle scattering of the primary beam leading to the disappearance of single particle trajectory features.Measurements of the BPD critical current have been carried out with an ion thruster (Kaufman engine) to provide a background plasma, and these indicate that the presence of an ambient plasma of typical ionospheric densities has little effect on the critical current relation.Measurements of wave amplitudes over a large frequency range show that the amplitude of waves near the plasma and electron cyclotron frequencies are too small to cause or sustain BPD, and that the important instabilities are at much lower frequency (～ 3 kHz in these measurements).     

Two dimensional simulation of amplitude modulated electron plasma waves

Highly modulated waves near electron plasma frequency with both parallel and perpendicular polarization have been observed near diffusion region at dayside and in the tail region. In this paper, two dimensional Particle-In-Cell (PIC) simulation was performed to study the possible generation mechanism of these modulated electron plasma waves. It is shown that weak beam instability could generate the modulated Langmuir wave and the ambient magnetic field plays an important role in the formation of modulation. When the weak beam has loss cone distribution, highly modulated upper hybrid waves are generated and propagate with large angle to the ambient magnetic field. The properties of these modulated waves are discussed and compared with observations.     

New aspects of whistler waves driven by an electron beam studied by a 3-D electromagnetic code

We have restudied electron beam driven whistler waves with a 3-D electromagnetic particle code. In the initialisation of the beam-plasma system, “quiet start” conditions were approached by including the poloidal magnetic field due to the current carried by beam electrons streaming along a background magnetic field. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, (2) the parallel phase velocity of the whistler wave is smaller than that of the beam mode, and (3) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is involved in the generation of the whistler waves.     

Instrument study of the Lunar Dust eXplorer (LDX) for a lunar lander mission

One of the highest-priority issues for a future human or robotic lunar exploration is the lunar dust. This problem should be studied in depth in order to develop an environment model for a future lunar exploration. A future ESA lunar lander mission requires the measurement of dust transport phenomena above the lunar surface. Here, we describe an instrument design concept to measure slow and fast moving charged lunar dust which is based on the principle of charge induction. LDX has a low mass and measures the speed and trajectory of individual dust particles with sizes below one micrometer. Furthermore, LDX has an impact ionization target to monitor the interplanetary dust background. The sensor consists of three planes of segmented grid electrodes and each electrode is connected to an individual charge sensitive amplifier. Numerical signals were computed using the Coulomb software package. The LDX sensitive area is approximately 400 cm². Our simulations reveal trajectory uncertainties of better than 2° with an absolute position accuracy of better than 2 mm.     

真空中连续发射电子束形成的电子鞘层的空间结构

用双流理论模型研究真空中电子束的发射实验。向真空中发射电子束过程中,发射体本身被充正电,束缚束电子向外传播,大量的束电子在发射体表面附近形成电子鞘层;只有极少量的束电子可以逃离发射体而向外传播出去。在电子鞘层内,发射出的束电子和返回发射体表面的束电子形成速度和密度在空间为分布不均匀的双流。本文用双流理论模型解析计算出了电子鞘层的空间尺度、电子鞘层内的电场分布以及电子密度分布。