Interaction of a shock wave with a magnetic field in a medium with finite conductivity

We consider the process of the interaction of aplanar shock wave with a magnetic field (impact on a magnetic wall) in a medium having finite conductivity.The problem cannot be solved analytically in the general form. Numerical methods are used to study the problem. A computer is used to calculate the complete system of one-dimensional nonsteady equations of MHD with finite conductivity which depends on temperature in a nonlinear fashion. Results are also presented of particular analytic solutions obtained under simplifying assumptions.We discuss the dependence of the process dynamics on the magnitude of the magnetic field intensity and the law of variation of the medium conductivity with temperature.In the numerical calculations we note the formation of a T-layer, a phenomenon which occurs under definite conditions in unsteady MHD problems [1].In conclusion the authors wish to thank N. G. Basov, A. A. Samarskli, and O. N. Krokhin for posing the problem and for fruitful discussions, and also D. A. Gol'din and A. A. Ivanov for carrying out the numerical calculations.     

Different modes of heating when high-power radiation fluxes interact with a material

The gas-dynamic and thermal processes which occur when a high-power flux of laser radiation interacts with a material are investigated. Fluxes for which the sublimation energy can be neglected compared with the thermal and kinetic energy of the vapors formed are considered. The electron thermal conductivity is considered as well as the hydrodynamic dispersion. The properties of different modes of propagation of temperature waves in a moving medium are studied. The case of an infinitely large absorption coefficient is given particular attention.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 41–48, September–October, 1972.The authors thank A. A. Samarskii for useful discussions.     

Mössbauer study of Fe powder mechanically alloyed by power ultrasonics

The Mössbauer and transmission electron microscopy (TEM) analysis of Fe-powder and Fe₄₆C₅₄-powder blend, mechanically milled by high power ultrasonics (USM) in He environment for 20–75 hours, have been carried out. As shown, the USM results in effective grinding of initial polycrystalline iron particles up to formation of single crystalline state, dissolution of carbon in iron particles, synthesis of carbides and possibly penetration of Fe atoms into graphite. Annealing of processed Fe₄₆C₅₄ powder causes carbide reaction.     

Effect of finite conductivity in a medium on shock-wave interaction with a magnetic field

We consider the problem of shock-wave incidence on a magnetic wall, which has been studied in [1]. It is shown that the dynamics of the processes which take place in this case depend significantly on the behavior of the conductivity-temperature dependence (T) of the medium and also on the magnitude of the magnetic-field intensity H₀.An exact solution of the problem is constructed for a special form of the law (T). For an arbitrary law (T) the problem is studied numerically by means of digital computer computations; the results are compared with the exact results.Analysis of these solutions shows that the dissipative properties of the medium (electrical conductivity, viscosity), which determine the structure of the refracted wave front, affect the nature of the entire flow as a whole.The formulated problem also makes it possible to clarify the characteristic features of the decay of a discontinuity in a conducting medium.The authors wish to thank A. A. Samarskii, L. A. Zaklyaz'minskii, L. M. Degtyarev, and A. P. Favorskii for discussions of the study, D. A. Gol'dina and A. A. Ivanov for carrying out the numerical calculations, and also G. A. Lyubimov for several helpful comments.     

Nonlinear Electrostatic Ion‐Acoustic Waves in the Solar Atmosphere

Basing on recent solar models, the excitation of ion‐acoustic turbulence in the weakly‐collisional, fully and partially‐ionized regions of the solar atmosphere is investigated. Within the frame of hydrodynamics, conditions are found under which the heating of the plasma by ion‐acoustic type waves is more effective than the Joule heating. Taking into account wave and Joule heating effects, a nonlinear differential equation is derived, which describes the evolution of nonlinear ion‐acoustic waves in the collisional plasma.     

Thermonuclear gain of a two-cascade laser-fusion target

One-dimensional numerical calculations are used to explore the possibility of thermonuclear fuel “ignition” (achieving an energy gainG ～ 1) in two-cascade laser-fusion targets with a relatively small aspect ratio for the inner shell. It is demonstrated that the parameters of the laser-produced thermonuclear plasma for a laser pulse energy of 200 kJ, various wavelengths of the laser radiation, and a simple pulse shape closely correspond to the “ignition” state for a target with an inner shell having an aspect ratio of ～ 3–10. This is indicative of the high energy efficiency of two-cascade targets that appear to be characterized by high reliability with respect to evolution of hydrodynamic instabilities.     

Allotropic forms of carbon in the Invar Fe–Ni–C alloy before and after plastic deformation by upsetting

The effect of cold plastic deformation by upsetting (e = 1.13) on structure and hybridised bonds of carbon in the fcc Invar Fe-30.9%Ni-1.23% C alloy was studied by means of X-ray phase analysis and X-ray photoelectron spectroscopy. Carbon precipitates along grain boundaries and inside of grains in the alloy after annealing and plastic deformation were revealed. The presence of mainly sp²- and sp³-hybridised C–C bonds attributing to graphite and amorphous carbon as well as the carbon bonds with impurity atoms and metallic Fe and Ni atoms in austenitic phase were revealed in the annealed and deformed alloy. It was shown for the first time that plastic deformation of the alloy results in partial destruction of the graphite crystal structure, increasing the relative part of amorphous carbon, and redistribution of carbon between structural elements as well as in a solid solution of austenitic phase.     

First Experiments on Generating and Receiving Artificial ULF (0.3–12 Hz) Emissions at a Distance of 1500 km

We present first results on generation and reception of an artificial ULF signal at distances of 800 and 1500 km in the frequency range 0.3–12 Hz. The high-sensitivity receiving equipment and a stable current in the antenna exciting the ULF field in the Earth-ionosphere cavity allowed us to detect the signal with high accuracy. It was found that the amplitude-frequency dependences and the polarization of an artificial signal are strongly different in the daytime and at night, which is related to the influence of the near-Earth waveguide and resonance structures on the detected signal. We calculate the signal amplitude for different models of the ionosphere. It is shown that the model of an anisotropic, vertically inhomogeneous ionosphere describes adequately the amplitude-frequency dependences of the measured ULF signal. We calculate the apparent resistance of the underlying surface at the reception point using two measured orthogonal components H_x and E_y of an electromagnetic field. It is shown that the calculation accuracy of the apparent resistance obtained using a controlled ULF source exceeds significantly the accuracy achieved using natural electromagnetic fields.