The Impact of Variable Accelerations on Crystal Growth onboard Spacecraft by the Floating Zone Method

The numerical investigation of the impact of time-dependent accelerations (vibrations) on the flow and heat and mass transfer in the melt is carried out for the case of modeling the crystal growth by the floating zone method under conditions of microgravity that exist onboard spacecraft. The effects of the Archimedean buoyancy force and of vibrations of the free surface of fluid are considered separately. When solving the problem of the effect of the vibrations of the free surface of fluid, the previously obtained data were used. It is shown that vibrations of the free surface have a much stronger effect on the processes under consideration than the buoyancy. Some problems that are related to the newly discovered effects are discussed. The use of vibroprotected systems and a rotating magnetic field can help solve these problems. We plan to continue our investigations in future spacecraft experiments, in particular, at the International Space Station, which is under construction at the moment.     

Gravitational Sensitivity of Melts at the Growth of InSb:Te Crystals by the Bridgman and Floating Zone Methods under the Conditions of Microgravity

The comparative analysis of the results of space and ground-based experiments IMET RAS on the growth of InSb:Te crystals by the Bridgman method and floating zone method (FZM) is made for the purpose of studying the influence of microgravity on the growth, structure, and properties of grown crystals, and thus the gravity sensitivity of InSb melt is demonstrated. It is shown that, under microgravity conditions, the Bridgman method makes it possible to grow InSb:Te crystals without contact with the ampoule walls, which provides for the single crystal structure, the absence of striations, and a low dislocation density. For the first time, InSb:Te monocrystals were grown with the FZM under microgravity. The anomalous behavior of the impurity core (facet effect) in these crystals correlates with the changed magnitude and direction of the quasi-stationary (residual) microaccelerations.     

Modeling of liquid encapsulated gallium melts

Liquid encapsulation crystal growth from the melt plays an important role in space processing. Use of an encapsulant may avoid evaporation of volatile components and may control thermocapillary flow, which becomes important in microgravity. In the present work the fluid physics of encapsulated liquid gallium is studied analytically and numerically in preparation to forthcoming experiments. It is shown that flow in the viscous encapsulant is essentially negligible and that liquid encapsulation reduces flow velocities in the encapsulated electronic melt. Flow velocity in the gallium is the main parameter in the studies.     

On the conditions of gas inclusions formation in melts under zero gravity state (after “Pirin” experiment)

Thermodynamics relations have been considered under which gas inclusions may form in melts (closed systems), due to both volatility of components and the presence of dissolved gases. It has been shown that in the melts with sufficient volatility of components, gas inclusions may form under equilibrium conditions if the ampoule is wetted well by the melt, whereas in case of low wettability they form under non-equilibrium state only. The foaming in the tellurium-selenium system has been analysed (“Pirin”, KP-4 experiment).In the melts containing dissolved gases, gas inclusions form under conditions of deviation from equilibrium and it is the main mechanism of outgassing. It has been demonstrated that the melt foaming method using hydrid compounds may be applied to the materials exhibiting a hysteresis of temperature dependence of diluted hydrogen concentration. Production of foam aluminium under zero gravity state has been considered as an example (“Pirin”, SP-3 experiment).     

Effects of Constant and Variable Accelerations on Crystals Grown onboard Spacecraft by the Method of Directional Crystallization

The effect of constant and time-dependent accelerations (vibrations) on the melt flow and heat and mass transfer in the process of crystal growth by the method of directional crystallization (Bridgman method) onboard spacecraft is numerically investigated. The mathematical formulation of the problem and the technique to solve it numerically are given. The time-averaged flow arising under the action of vibrations in a nonisothermal fluid is investigated. With the help of a rational choice of dimensionless similitude parameters, a generalized dependence on the intensity of melt flow is obtained for the radial segregation of dopants. This dependence is invariant with respect to the type of motive power and thermal boundary conditions in the region of very small velocities of melt flow (creeping flow), which are characteristic for microgravity conditions. The allowable levels of constant accelerations, as well as the frequency dependences of tolerable vibrations, are obtained for five typical semiconductor materials: Ge(Ga), GaAs(Te), InSb(Te), Si(P), and Si(B). It is shown that the radial segregation of dopant is much more sensitive to microaccelerations than the axial one. In the region of small velocities, the latter is determined by the duration of the transition regime, which depends on certain physical properties of the melt. New problems that resulted from the investigations performed are discussed.     

THEORETICAL ANALYSIS OF InP CRYSTAL GROWTH EXPERIMENT PERFORMED ON-BOARD RUSSIAN FOTON-11 SATELLITE

Traveling heater method (THM) experiments on InP crystal growth from indium solution (SKAT-FD) were performed during the Russian FOTON-11 mission in October 1997. The aim of these experiments was to ascertain the effectiveness of controlling heat and mass transfer in the liquid phase by applying a rotating magnetic field (RMF). As an effort to understand the parameters influencing the crystal growth a mathematical model was developed for numerical simulation of these experiments. The SKAT-FD crystals were grown with RMF at an induction of 1 and 2 mT. As the calculations show, such magnetic fields influence remarkably the hydrodynamics of the melt, and consequently, the growth process. The change of the magnetic induction value (or switching off the RMF) led to an abrupt change of the growth rate, measured from artificial dopant striations produced in the growing crystals by the heat-pulse technique.     

Prospects of autotrophic link functioning in biological life-support systems based on cell biology studies

On the basis of using of modern methods of cytological analysis the cell growth peculiarities, reproduction and structure of plant cells of different level organisation (unicellular algae, mosses, angiosperms, cell cultures of higher factors--weightlessness, hypogravity, magnetic fields of various intensity, vibration and acceleration were cleared. It is shown that many discovered biological effects of space flight are connected with the degree of complexity of the object organisation and intensified with the increasing duration of influence.     

Heat transfer of thermocapillary convection in a two-layered fluid system under the influence of magnetic field

Heat transfer of a two-layer fluid system has been of great importance in a variety of industrial applications. For example, the phenomena of immiscible fluids can be found in materials processing and heat exchangers. Typically in solidification from a melt, the convective motion is the dominant factor that affects the uniformity of material properties. In the layered flow, thermocapillary forces can come into an important play, which was first emphasized by a previous investigator in 1958. Under extraterrestrial environments without gravity, thermocapillary effects can be a more dominant factor, which alters material properties in processing. Control and optimization of heat transfer in an immiscible fluid system need complete understanding of the flow phenomena that can be induced by surface tension at a fluid interface. The present work is focused on understanding of the magnetic field effects on thermocapillary convection, in order to optimize material processing. That is, it involves the study of the complicated phenomena to alter the flow motion in crystal growth. In this effort, the Marangoni convection in a cavity with differentially heated sidewalls is investigated with and without the influence of a magnetic field. As a first step, numerical analyzes are performed, by thoroughly investigating influences of all pertinent physical parameters. Experiments are then conducted, with preliminary results, for comparison with the numerical analyzes.     

Investigation of thermosolutally caused convection during -growth of BiSbTe3-mixed crystals at normal and reduced gravity

BiSbTe₃-mixed crystals have been grown at normal and reduced gravity (during the MIR'97-mission) using a -configuration of the TITUS facility. The distribution of the components in the melt, and so the homogeneity of the growing crystal, is strongly influenced by the flow in the melt even in the case of weak convection. The flow configuration in the melt especially in front of the solid-liquid phase boundary can be investigated by means of a segregation analysis of the system components and an additional Pb-dopant. The BiSbTe₃-system is because of its hydro-dynamic properties a typical representative of semiconductor melts (low number, high number) but there are also some special properties relating to the segregationally caused enrichment of the lighter tellurium at the phase boundary and the resulting solutal destabilities. Experimental experiences from segregation analysis have shown that the mass transport in the melt at normal gravity is mainly influenced by convective mixing determined by thermally and solutally caused buoyancy forces. Numerical simulations have been performed for the real experimentally used configurations. These simulations have shown that a strong coupling of thermal and solutal effects exists and have given axial as well as radial segregation profiles being in excellent agreement with the experimental results for the vertical normal gravity grown crystals. For micro gravity conditions a reduction of the flow velocity of more than two orders of magnitude (depending on the micro gravity level and the direction of the residual acceleration) resulting in diffusion controlled component segregation has been predicted.The results of the two micro gravity grown crystals, especially the axial and radial segregation profiles as a sensitive indicator for the flow configuration in front of the phase boundary will be given and discussed in the paper. They will be compared with the results of numerical simulations of the melt flow for the real processing parameters measured during the TITUS growth processes and with experimental as well as numerical results for vertical normal gravity grown reference Samples.     

Investigation of thermosolutally caused convection during Bridgman-growth of BiSbTe3-mixed crystals at normal and reduced gravity

BiSbTe₃-mixed crystals have been grown at normal and reduced gravity (during the MIR'97-mission) using a Bridgman-configuration of the TITUS facility. The distribution of the components in the melt, and so the homogeneity of the growing crystal, is strongly influenced by the flow in the melt even in the case of weak convection. The flow configuration in the melt especially in front of the solid-liquid phase boundary can be investigated by means of a segregation analysis of the system components and an additional Pb-dopant. The BiSbTe₃-system is because of its hydro-dynamic properties a typical representative of semiconductor melts (low Prandtl number, high Schmidt number) but there are also some special properties relating to the segregationally caused enrichment of the lighter tellurium at the phase boundary and the resulting solutal destabilities. Experimental experiences from segregation analysis have shown that the mass transport in the melt at normal gravity is mainly influenced by convective mixing determined by thermally and solutally caused buoyancy forces. Numerical simulations have been performed for the real experimentally used configurations. These simulations have shown that a strong coupling of thermal and solutal effects exists and have given axial as well as radial segregation profiles being in excellent agreement with the experimental results for the vertical normal gravity grown crystals. For micro gravity conditions a reduction of the flow velocity of more than two orders of magnitude (depending on the micro gravity level and the direction of the residual acceleration) resulting in diffusion controlled component segregation has been predicted.The results of the two micro gravity grown crystals, especially the axial and radial segregation profiles as a sensitive indicator for the flow configuration in front of the phase boundary will be given and discussed in the paper. They will be compared with the results of numerical simulations of the melt flow for the real processing parameters measured during the TITUS growth processes and with experimental as well as numerical results for vertical normal gravity grown reference Samples.     

多种软磁合金及金属非晶材料的磁屏蔽性能研究

针对部分航天器组件易受磁场影响的问题,文章选取了6种目前常用的软磁合金及金属非晶材料,研究了它们对于弱磁场波动、稳恒磁场以及低频交流磁场的屏蔽效果,结果表明,材料的磁导率与矫顽力对磁屏蔽性能有较大影响,其中矫顽力与磁屏蔽性能的负相关性更好,即矫顽力越低,材料的磁屏蔽性能越好。对于测试的6种材料,铁镍合金材料与钴基非晶材料的磁屏蔽性能优于其他4种,铁镍合金材料在1 kHz以下磁屏蔽性能更佳,钴基非晶材料在50 kHz以下具有一定磁屏蔽效果。     

Vibration controlled convection — preparation and perspective of the Maxus 4 experiment

A comparatively new possibility to influence convection in crystal growth melts is the application of controlled interface vibration, especially in systems with free melt surfaces like the float-zone process. The present paper concerns the development and testing of a vibrational device which will be integrated into a microgravity crystal growth facility for the growth of silicon crystals. In the case of silicon grown by the float-zone technique, time-dependent thermocapillary convection is present even under mirogravity and leads to unfavourable variations of the crystal composition profile.The developed setup can operate in the range of approximately 0.1 to 50kHz producing maximum amplitudes of 0.25μm (non resonance case) and 3.5μm (resonance case) respectively. The power consumption is below 5W, the maximum operation temperature of the device is restricted to 200°C, limited by an epoxy-based connection between vibrator and sample. The first microgravity application will be during the European Maxus 4 campaign in April 2001.     

航天器铁路运输中的大承载低频减振技术

针对航天器铁路运输过程中传统钢丝绳减振系统多采用定制化设计且难以对低频振动进行有效减振的局限,提出一种可适用于不同航天器的通用模块化复合减振单元,通过空气弹簧压力及流阻调节控制实现减振系统在不同承载条件下的阻尼调节。在单元组件级研制和试验验证基础上,开展全减振系统研制和跑车试验。试验验证结果表明：减振单元具备阻尼比在0.18～0.29区间连续调节能力,与传统钢丝绳减振系统相比可明显降低运输过程中的振动响应,有效减振频率下限低至8～15 Hz,可为3000 kg以上的大型航天器的安全运输提供有力保障。     

On hydromagnetic flow of an Oldroyd-B fluid near a pulsating plate

An initial value investigation is made of the motion of an incompressible, viscoelastic, conducting Oldroyd-B fluid bounded by an infinite rigid non-conducting plate. The unsteady flow is generated from rest in the fluid due to velocity tooth pulses subjected on the plate in presence of an external magnetic field. It is assumed that no external electric field is acting on the system and the magnetic Reynolds number is very small. The operational method is used to obtain exact solutions for the fluid velocity and the shear stress on the plate. Quantitative analysis of the results are presented with a view to disclose the simultaneous effects of the magnetic field and the fluid elasticity on the flow and the wall shear stress for different periods of pulsation of the plate. It is shown that the classical and hydromagnetic Rayleigh solutions are limiting cases of the present analysis.     

Eddy currents induced migration of droplets in electrically conducting fluid in microgravity environments

Electrical eddy currents induced migration of droplets, whose conductivity differs from that of surrounding fluid, is analysed. Eddy currents in a dilute suspension under consideration, which fills the dielectric tube, are induced by alternating magnetic field parallel to the tube axis. In the case where the droplet radius is small as compared to the skin depth, the distributions of magnetic fields, currents and electromagnetic forces inside and outside the droplet have been calculated. For small Reynolds numbers, with neglecting inertial and thermocapillary effects and the gravity, the flow of fluids around the droplet and inside it, caused by electromagnetic forces, has been studied. The formula is obtained, which relates the droplet migration velocity to the electro-magnetic field, the droplet size and physical properties of fluids.     

Dust Plasma Dynamics in the Geomagnetic Tail

The results of numerical modeling of dust plasma dynamics in the geomagnetic tail are presented for the southward and northward orientations of the interplanetary magnetic field in the model with reconnection of magnetic field lines of geomagnetic and interplanetary magnetic fields. It is shown that in reconnection regions the compression shock waves arise, at the fronts of which the dust plasma fluxes with higher-than-background density are generated.     

Hydrodynamics during melting of an electroconductive sample in microgravity conditions under contactless positioning by electromagnetic forces

MHD-flow during melting of a spherical metal sample under contactless positioning by alternating magnetic field produced by two circular turns with currents, is investigated. It is shown that when the currents supplying the turns are opposite in direction, electromagnetic forces, originating from the interaction of the Foucault currents with alternating magnetic field, induce two torus-like eddies in the interior of the molten metal drop.     

脉冲风洞油流和液晶热图流动显示技术

介绍适合脉冲风洞进行表面流动显示的油流和液晶热图技术。前者用油滴流动迹线显示表面流线方向和形状，后者用液晶层反射光的波长（即颜色）分布显示表面温度分布。用这两种方法在定常流时间７ｍｓ至５００ｍｓ的脉冲风洞中成功地获得了尖前缘翼、钝翼和方向的三维干扰流油流和液晶热图清晰照片，清楚地显示出三维干扰流动特征。结果表明，用油流、液晶热图和薄膜电阻温度计热流分布测量得到的干扰流特征位置完全吻合，证实了显示方     

多自由度振动环境下惯组非线性传递特性研究

惯组作为飞行器姿控系统的传感器,其局部安装结构的传递特性的测量精度直接关系到导航精度。目前,惯组普遍使用减振器进行隔振,而减振器都呈现出较强的非线性特征。为了考察惯组在不同工况下的传递特性,将惯组简化为六自由度Duffing模型,推导了基础激励下系统的运动微分方程,并用龙格-库塔法对方程进行求解,分析了自由衰减振动和强迫振动下不同工况的系统传递特性。结果表明,多自由度激励比单自由度激励工况得到的系统传递特性的频率和幅值都低。考虑到惯组真实的使用环境,应当在多自由度振动环境下进行传递特性试验。