Spectroscopy of laboratory plasmas

Work under the heading of Laboratory Plasma Spectroscopy may be conveniently separated into three classes depending on the extent to which the interaction of the emitting atoms with their plasma environment is central to the investigation. Zero order, the longest established use of laboratory plasmas in connection with astrophysics, concerns the use of hot plasmas for the excitation, measurement, and identification of the spectra of highly-stripped ions. In such work the properties of the plasma itself are usually of secondary importance. In first-order, plasma spectroscopy is used to determine fundamental atomic data concerned with the interaction of an atom with a single particle, usually either a photon or an electron, i.e.: the determination of oscillator strengths and collision cross-sections. Finally, higher-order processes in which the plasma nature of the surrounding medium is most relevant concern the study of line-shapes, and related topics such as the excitation of satellite spectral features by plasma oscillations. Developments in plasma diagnostic techniques in the last five years have greatly extended the scope of the second and third categories and have yielded much astrophysically important information from laboratory studies. Recent advances in these areas are reviewed.     

Shock-wave structure in collisionless plasmas from results of laboratory experiments

Results of laboratory experiments on the study of collisionless shock wave structure in plasmas with and without a magnetic field are summarized, and comparisons with theoretical inferences are made. Consideration is given to the clarification of the collisionless dissipation mechanism and to the causes that bring it about. Transition conditions from one type of shock wave to another are analyzed. The relationship between laboratory experiments and the Earth bow shock measurements is also examined.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia.     

Stability and waves of transonic laboratory and space plasmas

The properties of magnetohydrodynamic waves and instabilities of laboratory and space plasmas are determined by the overall magnetic confinement geometry and by the detailed distributions of the density, pressure, magnetic field, and background velocity of the plasma. Consequently, measurement of the spectrum of MHD waves (MHD spectroscopy) gives direct information on the internal state of the plasma, provided a theoretical model is available to solve the forward as well as the inverse spectral problems. This terminology entails a program, viz. to improve the accuracy of our knowledge of plasmas, both in the laboratory and in space. Here, helioseismology (which could be considered as one of the forms of MHD spectroscopy) may serve as a luminous example. The required study of magnetohydrodynamic waves and instabilities of both laboratory and space plasmas has been conducted for many years starting from the assumption of static equilibrium. Recently, there is a outburst of interest for plasma states where this assumption is violated. In fusion research, this interest is due to the importance of neutral beam heating and pumped divertor action for the extraction of heat and exhaust needed in future tokamak reactors. Both result in rotation of the plasma with speeds that do not permit the assumption of static equilibrium anymore. In astrophysics, observations in the full range of electromagnetic radiation has revealed the primary importance of plasma flows in such diverse situations as coronal flux tubes, stellar winds, rotating accretion disks, and jets emitted from radio galaxies. These flows have speeds which substantially influence the background stationary equilibrium state, if such a state exists at all. Consequently, it is important to study both the stationary states of magnetized plasmas with flow and the waves and instabilities they exhibit. We will present new results along these lines, extending from the discovery of gaps in the continuous spectrum and low-frequency Alfvén waves driven by rotation to the nonlinear flow patterns that occur when the background speed traverses the full range from sub-slow to super-fast. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reconnective release of magnetic energy in astrophysical plasmas

Two particular examples are considered of astrophysical objects containing a highly conducting tenuous plasma with an excess magnetic energy supplied by an external source. The first example is the solar corona, whose magnetic field is continuously distorted by footpoint shuffling due to photospheric motions. The second case it an extragalactic jet extending from a galactic nucleus with an immersed magnetic field, and which is perturbed by variations in the pressure of the external medium. In both cases it is assumed that the system tends towards its lowest magnetic energy equilibrium via magnetic reconnection, thus providing a fast release of injected magnetic energy. Explicit relations between the characteristics of the external driver and the magnetic energy dissipation rate in these objects have been obtained. The relevance of this mechanism for heating the solar corona and maintaining radio emission from extragalactic jets is then. discussed by comparing these results with observational data.     

Tearing instability of reconnecting current sheets in space plasmas

Magnetic reconnection provides an efficient conversion of the so-called free magnetic energy to kinetic and thermal energies of cosmic plasmas, hard electromagnetic radiation, and accelerated particles. This phenomenon was found in laboratory and space, but it is especially well studied in the solar atmosphere where it manifests itself as flares and flare-like events. We review the works devoted to the tearing instability — the inalienable part of the reconnection process — in current sheets which have, inside of them, a transverse (perpendicular to the sheet plain) component of the magnetic field and a longitudinal (parallel to the electric current) component of the field. Such non-neutral current sheets are well known as the energy sources for flare-like processes in the solar corona. In particular, quasi-steady high-temperature turbulent current sheets are the energy sources during the main or hot phase of solar flares. These sheets are stabilized with respect to the collisionless tearing instability by a small transverse component of magnetic fiel, normally existing in the reconnecting and reconnected magnetic fluxes. The collision tearing mode plays, however, an important and perhaps dominant role for non-neutral current sheets in solar flares. In the MHD approximation, the theory shows that the tearing instability can be completely stabilized by the transverse fieldB _n if its value satisfies the conditionB _n /BS ^–3/4 B is the reconnecting component of the magnetic field just near the current sheet,S is the magnetic Reynolds number for the sheet. In this case, stable current sheets become sources of temporal spatial oscillations and usual MHD waves. The application of the theory to the solar atmosphere shows that the effect of the transverse field explains high stability of high-temperature turbulent current sheets in the solar corona. The stable current sheets can be sources of radiation in the radio band. If the sheet is destabilized (atB _n /BS ^–3/4) the compressibility of plasma leads to the arizing of the tearing instability in a long wave region, in which for an incompressible plasma the instability is absent. When a longitudinal magnetic field exists in the current sheet, the compressibility-induces instability can be dumped by the longitudinal field. These effects are significant in destabilization of reconnecting current sheets in solar flares: in particular, the instability with respect to disturbances comparable with the width of the sheet is determined by the effect of compressibility.     

Fields and plasmas in the outer solar system

The most significant information about fields and plasmas in the outer solar system, based on observations by Pioneer 10 and 11 investigations, is reviewed. The characteristic evolution of solar wind streams beyond 1 AU has been observed. The region within which the velocity increases continuously near 1 AU is replaced at larger distances by a thick interaction region with abrupt jumps in the solar wind speed at the leading and trailing edges. These abrupt increases, accompanied by corresponding jumps in the field magnitude and in the solar wind density and temperature, consist typically of a forward and a reverse shock. The existence of two distinct corotating regions, separated by sharp boundaries, is a characteristic feature of the interplanetary medium in the outer solar system. Within the interaction regions, compression effects are dominant and the field strength, plasma density, plasma temperature and the level of fluctuations are enhanced. Within the intervening quiet regions, rarefaction effects dominate and the field magnitude, solar wind density and fluctuation level are very low. These changes in the structure of interplanetary space have significant consequences for the many energetic particles propagating through the medium. The interaction regions control the access to the inner solar system of relativistic electrons from Jupiter's magnetosphere. The interaction regions and shocks appear to be associated with an acceleration of solar protons to MeV energies. Flare-generated shocks are observed to be propagating through the outer solar system with constant speed, implying that the previously recognized deceleration of flare shocks takes place principally near the Sun. Radial gradients in the solar wind and interplanetary field parameters have been determined. The solar wind speed is nearly constant between 1 and 5 AU with only a slight deceleration of 30 km s⁺¹ on the average. The proton flux follows an r ⁺² dependence reasonably well, however, the proton density shows a larger departure from this dependence. The proton temperature decreases steadily from 1 to 5 AU and the solar wind protons are slightly hotter than anticipated for an adiabatic expansion. The radial component of the interplanetary field falls off like r ⁺² and, on the average, the magnitude and spiral angle also agree reasonably well with theory. However, there is evidence, principally within quiet regions, of a significant departure of the azimuthal field component and the field magnitude from simple theoretical models. Pioneer 11 has obtained information up to heliographic latitudes of 16°. Observations of the interplanetary sector structure show that the polarity of the field becomes gradually more positive, corresponding to outward-directed fields at the Sun, and at the highest latitudes the sector structure disappears. These results confirm a prior suspicion that magnetic sectors are associated with an interplanetary current sheet surrounding the Sun which is inclined slightly to the solar equator.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978.     

Refractive Errors in Angle-of-Elevation Measurements

It is shown that the errors associated with radio elevation measurements may be investigated systematically using a variational technique. The error occurring when spaced antennas are used is compared with that for a single directional antenna. Integral expressions are obtained for the refractive errors.     

固体推进剂等离子体点火研究

为了研究等离子体对固体推进剂点火性能的影响，分别对双基药和硝胺药等两种固体推进剂，进行了等离子体点火实验。实验装置包括等离子体源、热电偶丝和动态信号分析仪。通过实验，获得了两种固体推进剂在不同的等离子体能量输入的条件下，其表面温度随时间变化的曲线。与常规点火数据相比，固体推进剂的等离子体点火延迟时间明显缩短。不同类型的固体推进剂，在相同的等离子体能量输入条件下，其点火性能不同；同一种类型的固体推进剂，在不同的等离子体能量输入条件下，其点火性能也不一样。     

Vlasov theory of the equilibrium structure of tangential discontinuities in space plasmas

Extensive theoretical work has been performed on the equilibrium structure of tangential discontinuities (TDs) in collisionless plasmas. This paper reviews kinetic models based on steady-state solutions of the Vlasov equation. It is shown that most of the existing models are special cases of a generalized multi-species model. In this generalized model all particle populations -from both outer regions and from inside the layer — are described using a unique formalism for the velocity distribution functions. Because of their historical importance, the Harris and Sestero models are reviewed and deduced from the generalized model. The Lee and Kan model is also a special case of the generalized model. The generalized model, however, is also able to describe TDs with velocity shear and large angles of magnetic field rotation. Such a multi-species model with a large number of free parameters and different gradient scales illustrates many observable features of TDs, including their multiscale fine structure. Particular attention is paid to the magnetopause. Observed magnetopause crossings are simulated. The effects of the relative flow velocity and asymmetrical magnetic field profiles on the structure of the magnetopause and on its stability with respect to tearing perturbations are discussed. We also present calculations that demonstrate the potential of the generalized model in explaining the origin of discrete auroral arcs. Numerical simulations of solar wind TDs with heavy ions and a large spectrum of thicknesses are also feasible. This indicates that such a model is of fundamental importance for understanding the detailed structure of solar wind TDs, like those observed by the interplanetary spacecraft ULYSSES. The problems associated with the one-dimensional, time-independent Vlasov approach are discussed and a variational principle is suggested to reduce the arbitrariness resulting from the large number of free parameters.     

电弧加热发动机温度和速度的测量

本文着重介绍光谱辐射法、激光诱导荧光法、静电探针法等接触式和非接触式测量技术在电弧加热发动机 (Arcjet)参数测量中的应用。讨论了电子温度、重粒子温度、羽流速度等参数的测量 ,并对一些结果进行了分析与论证 ,指出非热力学平衡态下不同的测量技术测量的是不同的温度指标。从测量技术的发展来看 ,激光测量技术将成为参数测量的主导技术。     

Energetic particle transport coefficients in the heliosphere

It is the purpose of this review to summarize and discuss recent research done in the field of particle propagation in the heliosphere. Several lines of approach have been followed to treat this problem. As a starting point the different forms of the transport equation are discussed. Quasi-Linear Theory (QLT) relates the power contained in fluctuations of the Interplanetary Magnetic Field (IMF) to the transport coefficients of energetic particles, an outline of the basic results of this theory is presented followed by a discussion of subsequent corrections made to the original formulation with an emphasis in recent developments where the effects of wave polarization, its propagation respect to the solar wind and the dissipation of power at large frequencies have been taken into account. The numerical approach using test particle trajectory integrations to obtain transport coefficients based on in situ satellite measureents is also discussed. It is well known that the determination of the particles mean free path for solar particle events by alternative methods leads to conflicting results, corrections made to original QLT are attempts to bridge the gap. Determination of the transport parameters from different lines of approach in a comparative basis have been done recently by calculating power spectra of IMF measured at the time solar particles were detected on the same spaceprobe, and performing numerical simulations with equivalent IMF data. Some of the results of such studies point to the solution of the conflicting determinations of the mean free path which has existed for nearly 30 years. An assesment of the present situation in this respect is given. Numerical determinations of transport parameters in the outer heliosphere are also reviewed and its consequences for solar modulation of galactic cosmic rays discussed. Space Science Reviews 62: Printed in Belgium.     

Energetic particle transport coefficients in the heliosphere

It is the purpose of this review to summarize and discuss recent research done in the field of particle propagation in the heliosphere. Several lines of approach have been followed to treat this problem. As a starting point the different forms of the transport equation are discussed. Quasi-Linear Theory (QLT) relates the power contained in fluctuations of the Interplanetary Magnetic Field (IMF) to the transport coefficients of energetic particles, an outline of the basic results of this theory is presented followed by a discussion of subsequent corrections made to the original formulation with an emphasis in recent developments where the effects of wave polarization, its propagation respect to the solar wind and the dissipation of power at large frequencies have been taken into account. The numerical approach using test particle trajectory integrations to obtain transport coefficients based on in situ satellite measureents is also discussed. It is well known that the determination of the particles mean free path for solar particle events by alternative methods leads to conflicting results, corrections made to original QLT are attempts to bridge the gap. Determination of the transport parameters from different lines of approach in a comparative basis have been done recently by calculating power spectra of IMF measured at the time solar particles were detected on the same spaceprobe, and performing numerical simulations with equivalent IMF data. Some of the results of such studies point to the solution of the conflicting determinations of the mean free path which has existed for nearly 30 years. An assesment of the present situation in this respect is given. Numerical determinations of transport parameters in the outer heliosphere are also reviewed and its consequences for solar modulation of galactic cosmic rays discussed. Space Science Reviews 62: Printed in Belgium.     

Critical phenomenon,crisis and transition to spatiotemporal chaos in plasmas

In a driven/damped drift-wave system a steady wave induces nonlinear variation of the dispersion of a perturbation wave (PW). Competition between the nonlinear dispersion with self-nonlinearity of the PW results in rich wave dynamic behaviors. In particular, a steady wave at the negative tangency slope of a hysteresis becomes unstable due to a saddle instability. It is found that such saddle steady wave (SSW) plays an important role in the discontinuous transition from a spatially coherent state to spatiotemporal chaos (STC). The transition is caused by a crisis due to a collision of the PW attactor to an unstable orbit of the SSW. In the time evolution, it is a ‘pattern resonance’ of the realized wave with the virtual SSW that triggers the crisis. The transition also displays as a critical phenomenon in parameter space, which is related to the change in the symmetry property of the motion of master mode (k = 1) of the PW with respect to that of SSW. In the spatially coherent state the former is trapped by the SSW partial wave, while in the STC it can become free from the latter, its trajectory crosses two unstable orbits of the SSW frequently, causing very turbulent behavior. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetohydrodynamic discontinuities in space plasmas: Interrelation between stability and structure

It is believed that shock waves and other discontinuous flows form the basis of a wide range of phenomena in space medium. We review the results concerning the particular property of MHD discontinuities, the interrelation between their stability and structure. Such an interrelation is associated primarily with the requirement of their evolutionarity. For a non-evolutionary discontinuity the amplitudes of reflected and refracted waves caused by a small amplitude incident wave are not determined unambiguously from the conservation laws at the discontinuity surface. Since the problem of the further time evolution of the initial small perturbation does not have a unique solution, such a discontinuity cannot exist in a real medium as a single steady-state configuration. Therefore it is unstable with respect to a disintegration into several discontinuities or to a transition to some more general unsteady flow. This is confirmed by the fact that, in the studied cases, the non-evolutionary shock transitions can, while the evolutionary ones cannot, be represented as a set of several discontinuities and waves of rarefaction. One more fundamental property of the non-evolutionary shocks that argues for their non-existence is that they do not have a unique structure for all values of the dissipative transport coefficients. At the same time, the possibility of their existence cannot be excluded when the shock has a unique structure or when the disintegration is forbidden for some reasons. Besides the non-evolutionarity, which is a direct reason for a disintegration, there is an indirect one. It can be shown that the hydrodynamic shocks without magnetic field that are corrugationally unstable also allow the shock transitions through more than one discontinuity. This suggests that the shocks unstable in the ordinary sense, for which the small perturbation grows with time, do not exist at all, but they disintegrate into stable ones. However, the physical mechanism that distinguishes between these two scenarios remains unclear. The interrelation between the stability and structure of MHD discontinuities thus governs their nonlinear evolution. This fact is essential when describing shock waves and other discontinuous flows in the space medium.     

利用TDLAS技术开展碳氢燃料高速燃气参数测量

可调谐二极管激光器吸收光谱技术(Tunable Diode Laser Absorption Spectroscopy,TDLAS)广泛应用于碳氢燃料燃气参数(温度、组分浓度和气流速度)实时在线和非接触测量。针对碳氢燃料火箭基组合循环(Rocket Based Combined Cycle,RBCC)发动机的高速燃气参数测量,设计了双交叉光束(7444.352+7444.371)/7185.597cm-1谱线对扫描波长-时分复用双线直接吸收光谱技术(Direct Absorption Spectroscopy,DAS)系统,将其应用于RBCC地面实验高速燃气参数在线测量,同时获得了燃气温度、H2O组分浓度和速度等多参数,并将测量结果与数值模拟计算结果对比,相对偏差不超过12%,这为RBCC发动机燃烧组织优化和结构优化提供重要依据。     

Statistical Measurements of Phase-Locked Receivers

Test instrumentation is described for use in the measurement of threshold sensitivities and noise bandwidths of narrow-band phase-locked receivers. The method is statistical in nature with the data being recorded digitally by a counter and printer. Scale factors can be selected for convenient relation of the data to the standard deviations, 1,2, or 3 sigma. Curves are included showing the results of a typical experiment.