Magnetic Gas Dynamics Research Articles

Influence of distance between coils with current on the effect of cascade plasma heating in flows injected from the QSPA

Research of the interaction of high-speed dense plasma flows generated by the quasi-stationary plasma accelerator with the magnetic field of the set of ring current-carrying conductors located at different distances from each other is presented. The study was based on the model of radiation magnetic gas dynamics, taking into account electrical conductivity, thermal conductivity and radiation transport. It was found that a decrease in the distance between the coils with a current leads to the disappearance of the effect of step-by-step or cascade transformation of kinetic energy into thermal energy of the plasma.

Implementing a Fully Conservative Lagrangian–Euler Scheme for Two-Dimensional Problems of Magnetic Gas Dynamics

An algorithm for the numerical solution of the equations of magnetic gas dynamics (MGD) approximated by a fully conservative Lagrangian–Euler difference scheme (FCDS) is considered. The complete system of equations for the dynamics of a high-temperature medium is solved taking into account the conductive (electronic, ionic) and radiative heat transfer. The calculation stage related to computations on a Lagrangian moving grid is implemented based on implicit approximations. The corresponding difference equations are solved by an iterative method with a sequential allowance for physical processes. Convergence estimates are obtained for various combinations of difference equations grouped according to physical processes. The obtained estimates are validated by computational experiments with model and applied problems.

The Using of DVM-System for Developing of a Program for Calculations of the Problem of Radiation Magnetic Gas Dynamics and Research of Plasma Dynamics in the QSPA Channel

DVM-system is designed for the development of parallel programs of scientific and technical calculations in the C-DVMH and Fortran-DVMH languages. These languages use a single DVMH-model of parallel programming model and are an extension of the standard C and Fortran languages with parallelism specifications in the form of compiler directives. The DVMH model makes it possible to create efficient parallel programs for heterogeneous computing clusters, in the nodes of which accelerators, graphic processors or Intel Xeon Phi coprocessors can be used as computing devices along with universal multi-core processors. The article describes the experience of the successful using of DVM-system to develop a parallel software code for calculating the problem of radiation magnetic gas dynamics and for research of plasma dynamics in the QSPA channel.

On some integral‐consistent methods for calculating magnetohydrodynamic phenomena in problems of computational astrophysics

When constructing difference schemes for calculating complex problems of computational astrophysics considering magnetohydrodynamic and gravitational phenomena, the processes of matter overcompression (with a change in density by several orders of magnitude) should be taken into account, and it is important at a discrete level to take into account the corresponding energy transformations of magnetohydrodynamic, gravitational, kinetic, and internal energy during the evolution of a star. This problem is solved by constructing completely conservative difference schemes in a view of these magnetohydrodynamic processes and self‐gravitating phenomena. In this work, to study and apply the difference methods for solving problems of magnetic gas dynamics, a discrete representation of symmetrized spatial deformations of the medium was obtained. The representation is consistent with changes in the magnetic, kinetic, and internal energies and does not lead to their distortions when the matter is overcompressed.

Study of the ionizing gas flow in the channel of plasma accelerator with different ways of gas inflow at the inlet

Numerical studies of the ionization process are presented for various ways of the gas supplying at the inlet of the coaxial channel of the quasi-stationary plasma accelerator. Simulation of two-dimensional axisymmetric flows of ionizing gas was carried out on the basis of the equations of radiation magnetic gas dynamics taking into account radiation transport. The approximation of local thermodynamic equilibrium in three-component medium consisting of atoms, ions, and electrons was used in the MHD model. It was determined that non-uniform gas inflow at the channel inlet leads to even greater instability of the pulsating unsteady flows of the ionizing gas in the plasma accelerator. The method of long characteristics was used in the 3D model of radiation transport, including the basic mechanisms of emission and absorption for different portions of the spectrum. The radiation field in the ionizing gas flow was determined, including the integral radiation characteristics and the spectral radiation intensities in the narrow ranges of frequencies or photon energies.

Accounting of spontaneous magnetic fields in Focus 3D code

To study the interaction of laser radiation with matter, the Focus 3D code is being developed. The Focus 3D code uses the finite volume method. Within the framework of the program, the solution of the equations of ideal magnetic gas dynamics in conservation-law form is realized. To remove the divergence of the magnetic field, the projection scheme is used. Accounting of spontaneous magnetic fields is realized. Test problems are proposed with an analytical solution for verifying the correctness of numerical realization of accounting for spontaneous magnetic fields. A second order of approximation is obtained for calculating the gradient of smooth functions by the Gauss gradient theorem. The convergence of the solution of the problem to an analytic solution on refined grids is shown.

Gas Dynamics and Magnetic Fields in Infrared Dark Clouds

Almost two decades ago, the discovery of a handful of Infrared Dark Clouds (IRDCs) heralded a new avenue for exploring the elusive early phases of massive star formation (Egan et al. 1998). Since then tremendous progress has been made in our understanding of these clouds. It is now well established that IRDCs are ubiquitous and harbor a broad spectrum of star forming stages. Thus studies of star formation and IRDCs are intricately tied together. I summarize some of the recent progress in understanding the magnetic field structure and gas dynamics in IRDCs in the context of high-mass star formation formation.

COSMOLOGICAL MAGNETOHYDRODYNAMIC SIMULATIONS OF GALAXY CLUSTER RADIO RELICS: INSIGHTS AND WARNINGS FOR OBSERVATIONS

Non-thermal radio emission from cosmic ray electrons in the vicinity of merging galaxy clusters is an important tracer of cluster merger activity, and is the result of complex physical processes that involve magnetic fields, particle acceleration, gas dynamics, and radiation. In particular, objects known as radio relics are thought to be the result of shock-accelerated electrons that, when embedded in a magnetic field, emit synchrotron radiation in the radio wavelengths. In order to properly model this emission, we utilize the adaptive mesh refinement simulation of the magnetohydrodynamic evolution of a galaxy cluster from cosmological initial conditions. We locate shock fronts and apply models of cosmic ray electron acceleration that are then input into radio emission models. We have determined the thermodynamic properties of this radio-emitting plasma and constructed synthetic radio observations to compare to observed galaxy clusters. We find a significant dependence of the observed morphology and radio relic properties on the viewing angle of the cluster, raising concerns regarding the interpretation of observed radio features in clusters. We also find that a given shock should not be characterized by a single Mach number. We find that the bulk of the radio emission comes from gas with T>5x10^7, \rho~10^(-28)-10^(-27) g/cm^3, with magnetic field strengths of 0.1-1.0 \mu G and shock Mach numbers of M~3-6. We present an analysis of the radio spectral index which suggests that the spatial variation of the spectral index can mimic synchrotron aging. Finally, we examine the polarization fraction and position angle of the simulated radio features, and compare to observations.

On a regularization of the magnetic gas dynamics system of equations

A brief derivation of a specific regularization for the magnetic gas dynamic system of equations is given in the case of general equations of gas state (in presence of a body force and a heat source). The entropy balance equation in two forms is also derived for the system.For a constant magnetic regularization parameter and under a standard condition on the heat source, we show that the entropy production rate is nonnegative.

Plasma equilibrium in the magnetic field of Galatea traps

A mathematical model of quasi-equilibrium plasma configuration around the current carrying wire in the Galatea magnetic trap is considered. It is separated by a finite distance from the conductor. The configuration is formed at the initial stage by increased electric current in the wire. After that, weak diffusion of the magnetic field in highly conductive plasma slowly destroys it. No magnetic gas dynamics (MGD) model of strong equilibrium configuration of this type exists.

Interaction of a plasma plume induced by a pulsed plasma thruster with an incident flow of rarefied magnetized plasma

A three-dimensional computational model and the results of the calculation for the dynamics of a plasma plume induced by a pulsed plasma thruster (PPT) in a magnetized flow of the ambient plasma are presented. A nonstationary expansion process of a PPT-induced plasma plume is studied in the ionospheric plasma over 100 µs after the start of a 6-microsecond plasma pulse. The parameters of the plasma plume in the PPT outlet section simulate the performance characteristics of a pulsed thruster PPT-4 (Pulsed Plasma Thruster 4 [3]) utilizing solid Teflon propellant. The magnetohydrodynamic (MHD) model of the process is based on the approximation of the ideal magnetic gas dynamics and makes it possible to predict the dynamics of a plasma bunch after the pulse termination during its interaction with the ambient medium and the magnetic field as well as the induced electric fields and currents in the vicinity of the expanding plasma

Works of A.A. Samarskii on Computational Mathematics

Abstract This is a review of the main results in computational mathematics that were obtained by the eminent Russian mathematician Alexander Andreevich Samarskii (February 19, 1919 – February 11, 2008). His outstanding research output addresses all the main questions that arise in the construction and justification of algorithms for the numerical solution of problems from mathematical physics. The remarkable works of A.A. Samarskii include statements of the main principles re- quired in the construction of difference schemes, rigorous mathematical proofs of the stability and convergence of these schemes, and also investigations of their algorith- mic implementation. A.A. Samarskii and his collaborators constructed and applied in practical calculations a large number of algorithms for solving various problems from mathematical physics, including thermal physics, gas dynamics, magnetic gas dynam- ics, plasma physics, ecology and other important models from the natural sciences.

Imitation of wave processes by generating an electric explosion of conductors in nonuniformly heated materials

A new method for imitating wave processes in nonuniformly heated materials by means of the electroexplosion of conductors was proposed. The problem of a planar high-current discharge initiated by the explosion of a foil in the air was solved in the 1D approximation of magnetic radiation gas dynamics with regard to the dependence of the conductivity of the foil on the density and temperature of the material during electroexplosion, a dependence that characterizes the specifics of the state of the material in various areas of the phase diagram. The main parameters of the electroexplosion setup were selected. A special construction of the loading unit was developed, which eliminates the effect of current contraction in a planar conductor and ensures a uniform distribution of current over the foil and, consequently, a uniform distribution of the pressure pulse momentum over the surface area of loading. A method for imitating the temperature profile in the sample was proposed. A procedure for measuring the integral pressure pulse momentum under conditions of intense electromagnetic disturbances was developed.

Investigation of the dynamics of radiative micropinch discharges

The dynamics of plasma cylinder compression by current pulses with a rise time of ∼100 nsec in the Z-pinch geometry has been considered. The numerical simulation has been performed in the approximation of one-dimensional magnetic radiation gas dynamics. In the calculations, real thermodynamic, transport, and optical properties of the plasma have been used. The radiation transfer is described in the multigroup approximation by the photon energy. The calculations have been performed for a pinch in xenon (radius ∼0.5 cm, energy E0 = 10–30 J, maximum current ∼30 kA). A detailed pattern of the dynamics of pinches has been investigated and the energy-to-radiation conversion efficiency has been determined.

Numerical Analysis of the Characteristics of an Arc in Laminar and Turbulent Gas Flows

The equations of magnetic gas dynamics are used to calculate the characteristics of an electric arc in a plasmotron channel versus the gas flow rate. The results obtained with the aid of the laminar and the two-parameter k–e model of turbulence with allowance for deviations from equilibrium in the plasma and for the swirling of the gas are compared with experimental data. The stability of a laminar flow to the effect of weak hydrodynamic perturbations is investigated.

Quantitative Analysis of Convective Flow of Nitrogen Gas and Air under Magnetic Field Gradient.

Recently, magnetic field gradients have been found to induce gas flow and promote combustion in diffusion flames. For example, when N2 gas stream was injected into air toward a weaker magnetic field, it was accelerated and behaved like a jet stream. This phenomenon was explained qualitatively by a magnetic attractive force acting on paramagnetic oxygen gas. In this study, such a magnetically induced jet stream of N2 gas was quantitatively analyzed. First, the magnetic body force acting on the gas flow and the governing equation of magnetic gas dynamics are presented. Using them, a numerical simulation was carried out for N2-Air convective flow under a magnetic field gradient. Calculated results show that the jet flow is accelerated to 80 cm/sec when the initial N2 gas velocity is 3.9 cm/sec and maximum magnetic induction is 1.5 T. Furthermore, calculation shows the existence of a convective air flow around the N2 jet flow. The results of the present study show good agreement with the experimental results.

Estimates and stabilization of finite-difference equations of one-dimensional gravital magnetic gas dynamics

Estimates and stabilization of finite-difference equations of one-dimensional gravital magnetic gas dynamics

Dynamics of the z pinch with a light liner. II. Single-envelope liners and the anomalies of the cumulation stage

The results of calculations of the compression of single-envelope liners toward the axis in the one-dimensional magnetic radiative gas dynamics approximation are considered. A refinement is proposed for the method of calculating the cumulation stage, making it possible to obtain better agreement with experimental data.

Two-level finite-difference schemes for one-dimensional equations of magnetic gas dynamics (viscous heat-conducting case)

Article Two-level finite-difference schemes for one-dimensional equations of magnetic gas dynamics (viscous heat-conducting case) was published on January 1, 1989 in the journal Russian Journal of Numerical Analysis and Mathematical Modelling (volume 4, issue 3).

A difference scheme on a non-uniform mesh for the equations of one-dimensional magnetic gas dynamics

A new difference scheme for the equations of the one-dimensional motion of a viscous heat-conducting gas in a magnetic field is studied. In the non-linear statement of the problem, the existence, uniqueness, and stability of the solution of the scheme are proved and error estimates are obtained in terms of the data. All the results are obtained in the large with respect to time.