A linear accelerator for simulating micrometeorites

The theory, the estimated parameters, and the design features of the linear accelerator capable of accelerating charged dust particles 0.1–10 μm in diameter to velocities of 12 km/s are presented. The electrodynamical circuit of the accelerator is composed of 27 acceleration gaps, each of which is held at a potential of 20 kV. Particles are injected into the linear electrodynamical accelerator after preliminary acceleration in the linear electrostatic accelerator with an effective voltage of 145 kV. The total effective accelerating voltage is 670 kV. The total length of the accelerating sections is 3.62 m. The essential difference of this accelerator from the existing machines is that the drift tubes of the dynamical circuit are identical and that synchronism of particle motion with the voltage applied to the drift tubes is achieved by forming the accelerating voltage as a function of the particle velocity and specific charge. The measured performance data of the accelerator are presented.     

3 MV hypervelocity dust accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies

A hypervelocity dust accelerator for studying micrometeorite impacts has been constructed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS) at the University of Colorado. Based on the Max-Planck-Institu?t fu?r Kernphysik (MPI-K) accelerator, this accelerator is capable of emitting single particles of a specific mass and velocity selected by the user. The accelerator consists of a 3 MV Pelletron generator with a dust source, four image charge pickup detectors, and two interchangeable target chambers: a large high-vacuum test bed and an ultra-high vacuum impact study chamber. The large test bed is a 1.2 m diameter, 1.5 m long cylindrical vacuum chamber capable of pressures as low as 10(-7) torr while the ultra-high vacuum chamber is a 0.75 m diameter, 1.1 m long chamber capable of pressures as low as 10(-10) torr. Using iron dust of up to 2 microns in diameter, final velocities have been measured up to 52 km/s. The spread of the dust particles and the effect of electrostatic focusing have been measured using a long exposure CCD and a quartz target. Furthermore, a new technique of particle selection is being developed using real time digital filtering techniques. Signals are digitized and then cross-correlated with a shaped filter, resulting in a suppressed noise floor. Improvements over the MPI-K design, which include a higher operating voltage and digital filtering for detection, increase the available parameter space of dust emitted by the accelerator. The CCLDAS dust facility is a user facility open to the scientific community to assist with instrument calibrations and experiments.     

A Gas–Dust Impact Mass Spectrometer

A mass spectrometer for analyzing the elemental composition of micrometeorites and technogenic particles in space is described. A method for improving the mass-spectrometer resolution is proposed. The method is based on the time variations in the parameters of the accelerating electric field. The advantages of this gas–dust impact mass spectrometer over the analogs are a larger working area and a higher resolution at comparable masses and sizes. Using a combined construction for both particles and gas, it is possible to eliminate products of spacecraft degassing from a spectrum, thus improving the reliability of the results, and obtain information on the gas component of the external spacecraft atmosphere.     

Measurement of re-suspended road dust emission factor using mobile laboratory and flux tower

Re-suspended road dust is one of the main urban atmospheric pollutants. Thus, systematic management of polluted roads is essential, which requires precise measurement of re-suspended road dust emission factors. A mobile laboratory (ML) and a flux tower (FT) were used to measure re-suspended road dust. Re-suspended road dust concentration was measured while driving the ML at speeds of 40, 50, and 60 km/h along straight sections of five different roads in Incheon City, Korea. The correlation between measurements using the ML and the FT was anlyzed according to the ML speed. The results revealed a linear relationship between the mass concentration measured by the ML and the emission factor obtained from the FT. At faster ML speeds, the same emission factor was associated with higher concentrations measured by the ML. Thus, if the ML measurements are adjusted for the ML speed by employing the methods of this study, re-suspended road dust emission factors can be measured more accurately. Based on these findings, it is expected that the use of the MLs will contribute to reducing re-suspended road dust by enabling more effective management of road pollution levels.

     

Large area mass analyzer instrument for the chemical analysis of interstellar dust particles

A new instrument to analyze the chemical composition of dust particles in situ in space has been developed. The large target area ( approximately 0.2 m(2)) makes this instrument well suited for detecting a statistically significant number of interstellar dust grains or other dust particles with a low flux. The device is a reflectron-type time-of-flight mass spectrometer that uses only flat electrodes for the generation of the parabolic potential. The instrument analyzes the ions from the impact generated plasma due to hypervelocity dust impacts onto a solid target surface. The SIMION ion optics software package is used to investigate different potential field configurations and optimize the mass resolution and focusing of the ions. The cylindrically symmetric instrument operates with six ring electrodes and six annular electrodes biased to different potentials to create the potential distribution of the reflectron. The laboratory model of the instrument has been fabricated and tested. Hypervelocity dust impacts are simulated by laser ablation using a frequency doubled Nd:YAG laser with approximately 8 ns pulse length. The experimental data show typical mass resolution m/Deltam approximately 200.     

Invited article: Electric solar wind sail: toward test missions

The electric solar wind sail (E-sail) is a space propulsion concept that uses the natural solar wind dynamic pressure for producing spacecraft thrust. In its baseline form, the E-sail consists of a number of long, thin, conducting, and centrifugally stretched tethers, which are kept in a high positive potential by an onboard electron gun. The concept gains its efficiency from the fact that the effective sail area, i.e., the potential structure of the tethers, can be millions of times larger than the physical area of the thin tethers wires, which offsets the fact that the dynamic pressure of the solar wind is very weak. Indeed, according to the most recent published estimates, an E-sail of 1 N thrust and 100 kg mass could be built in the rather near future, providing a revolutionary level of propulsive performance (specific acceleration) for travel in the solar system. Here we give a review of the ongoing technical development work of the E-sail, covering tether construction, overall mechanical design alternatives, guidance and navigation strategies, and dynamical and orbital simulations.     

过山车动力学建模与仿真

过山车相对轨道做高速运动,其动态响应对过山车的舒适性、安全性有重要影响.利用ADAMS建立过山车动力学模型,对其进行了动力学仿真分析,阐述了建立过山车动力学分析模型的关键问题处理方法,并进行正常风速下的动力学分析.分析比较了风速对过山车动力学运动速度的影响.过山车的整个运动过程仿真分析速度结果与实际实验测试结果误差在6.4%以内,表明模型是合理的.     

First real-time detection of surface dust in a tokamak

The first real-time detection of surface dust inside a tokamak was made using an electrostatic dust detector. A fine grid of interlocking circuit traces was installed in the NSTX vessel and biased to 50 V. Impinging dust particles created a temporary short circuit and the resulting current pulse was recorded by counting electronics. The techniques used to increase the detector sensitivity by a factor of ×10,000 to match NSTX dust levels while suppressing electrical pickup are presented. The results were validated by comparison to laboratory measurements, by the null signal from a covered detector that was only sensitive to pickup, and by the dramatic increase in signal when Li particles were introduced for wall conditioning purposes.     

Dust trajectory sensor: accuracy and data analysis

The Dust Trajectory Sensor (DTS) instrument is developed for the measurement of the velocity vector of cosmic dust particles. The trajectory information is imperative in determining the particles' origin and distinguishing dust particles from different sources. The velocity vector also reveals information on the history of interaction between the charged dust particle and the magnetospheric or interplanetary space environment. The DTS operational principle is based on measuring the induced charge from the dust on an array of wire electrodes. In recent work, the DTS geometry has been optimized [S. Auer, E. Grün, S. Kempf, R. Srama, A. Srowig, Z. Sternovsky, and V Tschernjawski, Rev. Sci. Instrum. 79, 084501 (2008)] and a method of triggering was developed [S. Auer, G. Lawrence, E. Grün, H. Henkel, S. Kempf, R. Srama, and Z. Sternovsky, Nucl. Instrum. Methods Phys. Res. A 622, 74 (2010)]. This article presents the method of analyzing the DTS data and results from a parametric study on the accuracy of the measurements. A laboratory version of the DTS has been constructed and tested with particles in the velocity range of 2-5 km/s using the Heidelberg dust accelerator facility. Both the numerical study and the analyzed experimental data show that the accuracy of the DTS instrument is better than about 1% in velocity and 1° in direction.     

In-flight calibration of mesospheric rocket plasma probes

Many effects and factors can influence the efficiency of a rocket plasma probe. These include payload charging, solar illumination, rocket payload orientation and rotation, and dust impact induced secondary charge production. As a consequence, considerable uncertainties can arise in the determination of the effective cross sections of plasma probes and measured electron and ion densities. We present a new method for calibrating mesospheric rocket plasma probes and obtaining reliable measurements of plasma densities. This method can be used if a payload also carries a probe for measuring the dust charge density. It is based on that a dust probe's effective cross section for measuring the charged component of dust normally is nearly equal to its geometric cross section, and it involves the comparison of variations in the dust charge density measured with the dust detector to the corresponding current variations measured with the electron and/or ion probes. In cases in which the dust charge density is significantly smaller than the electron density, the relation between plasma and dust charge density variations can be simplified and used to infer the effective cross sections of the plasma probes. We illustrate the utility of the method by analysing the data from a specific rocket flight of a payload containing both dust and electron probes.     

深空一号飞行中的多功能结构技术试验

洛克希德．马丁宇航公司已开发出作为宇宙飞船设计新系统的多功能结构（MFS）概念,它淘汰了机箱、电缆、连接器并把电子设备封装进行宇宙飞船的壁中,协作工程学对于把电子、结构和热设计集成看成是最重要的。设计的方法是在工作中控制所有的功率,接地和屏蔽的关系。MFS方法提供了重要的重量和体积节省并在新的宇宙飞船计划中支持“更快、更好、更省”的哲学。该技术在新千年计划深空一号（DSI1）任务的试验中将得到证明。     

Recent developments in the ion/ion chemistry of high-mass multiply charged ions

The ability to form multiply charged high-mass ions in the gas-phase, most notably via electrospray ionization (ESI), has allowed the study of many different combinations of positively and negatively charged ions. The charged products are directly amenable to study with mass spectrometry. Ion/ion reactions have proved to be "universal" in the sense that the high exothermicities and large rate constants associated with essentially any combination of oppositely charged ions lead to reaction regardless of the chemical functionalities associated with the ions. These characteristics make ion/ion reactions potentially analytically useful provided reagent ion densities and spatial overlap of the oppositely charged ions are high. These conditions can be readily met by several instrumental configurations. The focus of this review is to highlight developments in this field since 1998. Novel instrumentation has been developed to study ion/ion reactions, such as atmospheric pressure ion/ion reactors followed by mass analysis, or electrodynamic ion trap mass spectrometers, which are used as reaction vessels at sub-atmospheric pressures. A wide variety of reaction phenomenologies have been observed in various ion/ion reactions, with proton transfer being the most common. New phenomenologies have been observed in the reactions of multiply charged positive ions with singly charged negative ions, including cation transfer and cation exchange. A new series of reactions between multiply charged positive ions and multiply charged negative ions have been made possible by recent instrumentation developments. These reactions have led to the observation of proton transfer and complex formation. These observations have provided new insights into ion/ion reaction dynamics and a bound orbit model appears to best account for experimental results. New applications are also discussed for a several ion/ion reaction.     

Impact dynamics of rough and surface protected MEMS gears

The paper provides an analysis of dynamics of micro-gear pairs, typically used in an assortment of micro-electromechanical system (MEMS) devices. It includes a mathematical hierarchical model of the impact dynamics of meshing gear teeth. It comprises the nanoscopic effect of asperity tips’ adhesion for relatively rough surfaces on a microscopic level (overall contact domain). The analysis is extended to the depletion of long chain molecule self-assembled molecules (SAM) in impact behaviour of meshing gear-teeth pairs. The analyses show that for the usual high operating speeds of MEMS gears, due to high impact velocities, the role of asperity tips’ adhesion is quite insignificant. However, the same is not true for lower impact velocities, which would occur under start-up, run-up to normal operating speeds or during deccelerative motions. The paper proposes a novel spectral-based approach to predict the degradation of the protective SAM layer between meshing teeth, while the mechanism is in continual relative motion.     

Performance tests of a new non-invasive sensor unit and ultrasound electronics

Industrial applications involving pulsed ultrasound instrumentation require complete non-invasive setups due to high temperatures, pressures and possible abrasive fluids. Recently, new pulser-receiver electronics and a new sensor unit were developed by Flow-Viz. The complete sensor unit setup enables non-invasive Doppler measurements through high grade stainless steel. In this work a non-invasive sensor unit developed for one inch pipes (22.5 mm ID) and two inch pipes (48.4 mm ID) were evaluated. Performance tests were conducted using a Doppler string phantom setup and the Doppler velocity results were compared to the moving string target velocities. Eight different positions along the pipe internal diameter (22.5 mm) were investigated and at each position six speeds (0.1–0.6 m/s) were tested. Error differences ranged from 0.18 to 7.8% for the tested velocity range. The average accuracy of Doppler measurements for the 22.5 mm sensor unit decreased slightly from 1.3 to 2.3% across the ultrasound beam axis. Eleven positions were tested along the diameter of the 48.4 mm pipe (eight positions covered the pipe radius) and five speeds were tested (0.2–0.6 m/s). The average accuracy of Doppler measurements for the 48.4 mm sensor unit was between 2.4 and 5.9%, with the lowest accuracy at the point furthest away from the sensor unit. Error differences varied between 0.07 and 11.85% for the tested velocity range, where mostly overestimated velocities were recorded. This systematic error explains the higher average error difference percentage when comparing the 48.4 mm (2.4–5.9%) and 22.5 mm (1.3–2.3%) sensor unit performance. The overall performance of the combined Flow-Viz system (electronics, software, sensor) was excellent as similar or higher errors were typically reported in the medical field. This study has for the first time validated non-invasive Doppler measurements through high grade stainless steel pipes by using an advanced string phantom setup.     

Simulation of micrometeorites using an electrodynamical accelerator

Results of experiments with a multiparameter detector of high-speed dust particles are presented. This detector is composed of induction (a Faraday cup), ionization, and photoelectric sensors. It allows simulation of micrometeorites over wide ranges of masses and velocities by measuring secondary effects due to collisions of particles with a wall. Experiments aimed at detecting high-speed dust particles have been carried out using an electrodynamical accelerator with an effective accelerating voltage of ∼650 kV. Original Russian Text ? N.D. Semkin, K.E. Voronov, A.V. Piyakov, I.V. Piyakov, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 4, pp. 159–165.     

A mechanistic model for the prediction of ductile erosion

Mechanisms operative in dust erosion of ductile materials were determined with the aid of scanning electron microscope studies. Dimensional analysis was employed in the development of a mathematical model for predicting the erosion of ductile materials. The basis of the model was an identified erosion mechanism (target melting) and the model was verified in an erosion testing program. The target materials in the testing program were three stainless steels, two aluminum alloys, a beryllium copper alloy and a titanium alloy. The erosive agents were three dusts with hard angular particles and one dust with spherical particles. Maximum particle velocities were 130 or 250 ms^?1.     

Probe diagnostics of laboratory and ionospheric rarefied plasma flows

A procedure is developed and formulas are obtained for processing and analyzing output signals of neutral-particle detectors (pressure probe) and current-voltage characteristics of a single cylindrical Langmuir probe, when high-speed nonequilibrium rarefied plasma flows are diagnosed on board a spacecraft in the ionosphere and on a test bench. The results are supported by experimental data. The procedure is intended to evaluate values of a set of basic kinetic parameters of neutral and charged particles of partially ionized rarefied gas flows.     

直读粉尘浓度测量仪表检定装置的研究

本文根据作者多年粉尘仪表检测的经验和研究成果,分析了影响直读式粉尘浓度测量仪表检定装置性能的各关键环节,提出了设计该装置的合理化建议,为设计者提供了部分关键问题的解决途径或思路。该思路能够指导设计者最终设计出既满足市场需要,又满足量传技术要求的检定装置,尽快解决目前基层计量站直读式粉尘浓度测量仪表量值溯源困难的问题。     

Emerging chemical sensor technologies for use in on-line applications

Advances in instrumentation and process control capabilities are being driven by the increased sensitivity of analytical chemistry methods, the commoditization and ruggedization of instruments and associated electronics, and changing consumer concerns and expectations, as well as government regulations. The emergence of biotechnology methods for the detection of contaminants, and the miniaturization and ruggedization of more standard analytical instruments based on mass spectrometry and infrared spectroscopy will be discussed as related to on-line process monitoring.     

Fracture of notched and perforated polymeric bars produced by longitudinal impact

An experimental investigation was executed to ascertain the stress intensity factors at the tip of stationary or moving cracks and the stress distribution at central holes in thin rectangular specimens of polymethyl methacrylate (PMMA) and polycarbonate of bisphenol (Lexan) as the result of longitudinal impact by 10 mm dia. steel spheres at velocities ranging from 15 to 130 m/s and by the hammers of standard Charpy impact testers. The initial and rebound velocities of the spheres as well as the strain histories in the specimens were measured. Crack kinematics, the stress intensity factor at the tip and the nominal stress at central holes were ascertained by means of a shadowgraphic technique using a 24-spark Cranz-Schardin camera.Stepwide propagation in the PMMA specimens, frequently found for low sphere-impact velocities, occurred at crack speeds of 250–340 m/s, while catastrophic failure in a single pass of the crack involved tip speeds from 625 to 700 m/s. For the Lexan samples, the velocities of all cracks whether moving intermittently or continuously, were observed to be between 435 and 510 m/s; thus, the average of the fast crack speeds corresponds to about 31% of the rod wave velocity for both materials. Dynamic stress intensity factors were found to be equal to or larger than corresponding static values of fracture toughness, and their variation with nominal stress in the bar followed different mechanical-optical paths during loading and unloading. Stress histories at holes in PMMA determined from strain gage data indicated a stress concentration when compared to those obtained from the shadowgraphs. Current analyses of the process based on static stress distributions in an infinite elastic plate under constant load require modification to provide an explanation of some of the phenomena observed. Such dynamic stress conditions in the vicinity of a crack or hole will also require an alteration of the photomechanical relations currently employed to ascertain crack tip intensity factors and stress conditions at circular holes determined from the geometry of shadow-graphic patterns.