An experimental study of transverse ionizing MHD shock waves

1968 ◽  
Vol 2 (4) ◽  
pp. 633-652 ◽  
Author(s):  
Charlles F. Stebbins ◽  
George C. Vlases
Keyword(s):  
Magnetic Field ◽  
Shock Waves ◽  
High Speed ◽  
Initial Conditions ◽  
Easy Access ◽  
Low Speed ◽  
Wide Range ◽  
Image Position ◽  
Shock Jump Relations ◽  
The Magnetic Field

The jump conditions across a transverse ionizing MHD shock wave, where the magnetic field is in the plane of the shock, are examined. The conservation laws, in conjunction with Maxwell's laws and the equation of state, yield three jump equations in four unknowns. To uniquely describe jumps across an ionizing wave requires an additional descriptive relationship. The theory of Kulikovskii & Lyubimov and, later, Chu, in which the internal structure of the shock itself supplies the missing relationship, is examined. In particular, Kulikovskii & Lyubimov show, for appropriate ratios of thermal to magnetic diffusivities, that for low-speed waves the magnetic field compression across the shock is unity and the jump equations reduce to the ordinary Rankine—Hugoniot relations. For high-speed shock waves, the magnetic field compression, B2/B1, equals the gas compression across the wave, p2/p1, and the jump equations become the magnetohydrodynamic shock jump relations. Furthermore, intermediate speed shocks induce magnetic field compressions between 1 and p2/p1. An experiment was performed in an inverse pinch where E behind the shock, the shock and piston velocities, and the magnetic field compression across the shock, were measured over a wide range of initial conditions and shock velocities in hydrogen. The jump relations were written with B2/B1 as a parameter and programmed into a digital computer. The program was written for real, equilibrium hydrogen. The program provided easy access to a unique solution of the jump equations for any B2/B1. The experiment tends to confirm the Kulikovskii—Lyubimov—Chu theory. Ordinary shock waves were observed at low speeds and near-MilD shocks were observed at high speeds. Further, the relation was verified for the plasma behind the shock for low-speed shock waves, and was verified to within experimental accuracy for the intermediate class of shock waves.

scholarly journals Hybrid Simulation of Solar-Wind-Like Turbulence

Solar Physics ◽  
2019 ◽  
Vol 294 (11) ◽  
Author(s):  
D. Aaron Roberts ◽  
Leon Ofman
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Speed ◽  
Radial Flow ◽  
Initial Conditions ◽  
Thermal Fluctuations ◽  
Flow Speed ◽  
Initial State ◽  
Simplifying Assumptions ◽  
The Magnetic Field

Abstract We present 2.5D hybrid simulations of the spectral and thermodynamic evolution of an initial state of magnetic field and plasma variables that in many ways represents solar wind fluctuations. In accordance with Helios near-Sun high-speed stream observations, we start with Alfvénic fluctuations along a mean magnetic field in which the fluctuations in the magnitude of the magnetic field are minimized. Since fluctuations in the radial flow speed are the dominant free energy in the observed fluctuations, we include a field-aligned $v_{\|}(k_{\perp })$v∥(k⊥) with an $k^{ -1}$k−1 spectrum of velocity fluctuations to drive the turbulent evolution. The flow rapidly distorts the Alfvénic fluctuations, yielding spectra (determined by spacecraft-like cuts) transverse to the field that become comparable to the $k_{\|}$k∥ fluctuations, as in spacecraft observations. The initial near constancy of the magnetic field is lost during the evolution; we show this also takes place observationally. We find some evolution in the anisotropy of the thermal fluctuations, consistent with expectations based on Helios data. We present 2D spectra of the fluctuations, showing the evolution of the power spectrum and cross-helicity. Despite simplifying assumptions, many aspects of simulations and observations agree. The greatly faster evolution in the simulations is at least in part due to the small scales being simulated, but also to the non-equilibrium initial conditions and the relatively low overall Alfvénicity of the initial fluctuations.

scholarly journals Intermediate shock sub-structures within a slow-mode shock occurring in partially ionised plasma

2019 ◽  
Vol 626 ◽  
pp. A46 ◽  
Author(s):  
B. Snow ◽  
A. Hillier
Keyword(s):  
Magnetic Field ◽  
Initial Conditions ◽  
Frictional Heating ◽  
Physical Parameters ◽  
Solar Chromosphere ◽  
Finite Width ◽  
Slow Mode ◽  
Wide Range ◽  
Intermediate Shock ◽  
The Magnetic Field

Context. Slow-mode shocks are important in understanding fast magnetic reconnection, jet formation and heating in the solar atmosphere, and other astrophysical systems. The atmospheric conditions in the solar chromosphere allow both ionised and neutral particles to exist and interact. Under such conditions, fine sub-structures exist within slow-mode shocks due to the decoupling and recoupling of the plasma and neutral species. Aims. We study numerically the fine sub-structure within slow-mode shocks in a partially ionised plasma, in particular, analysing the formation of an intermediate transition within the slow-mode shock. Methods. High-resolution 1D numerical simulations were performed using the (PIP) code using a two-fluid approach. Results. We discover that long-lived intermediate (Alfvén) shocks can form within the slow-mode shock, where there is a shock transition from above to below the Alfvén speed and a reversal of the magnetic field across the shock front. The collisional coupling provides frictional heating to the neutral fluid, resulting in a Sedov-Taylor-like expansion with overshoots in the neutral velocity and neutral density. The increase in density results in a decrease of the Alfvén speed and with this the plasma inflow is accelerated to above the Alfvén speed within the finite width of the shock leading to the intermediate transition. This process occurs for a wide range of physical parameters and an intermediate shock is present for all investigated values of plasma-β, neutral fraction, and magnetic angle. As time advances the magnitude of the magnetic field reversal decreases since the neutral pressure cannot balance the Lorentz force. The intermediate shock is long-lived enough to be considered a physical structure, independent of the initial conditions. Conclusions. Intermediate shocks are a physical feature that can exist as shock sub-structure for long periods of time in partially ionised plasma due to collisional coupling between species.

Monte Carlo calculation of the energy parameters and spatial distribution of the cathodic arc ions while passing through the macro-particles filters

2018 ◽  
Vol 1 (1) ◽  
pp. 30-34 ◽  
Author(s):  
Alexey Chernogor ◽  
Igor Blinkov ◽  
Alexey Volkhonskiy
Keyword(s):  
Magnetic Field ◽  
Mass Transfer ◽  
Monte Carlo ◽  
Monte Carlo Calculation ◽  
Inhomogeneous Magnetic Field ◽  
Flow Energy ◽  
Wide Range ◽  
Field Concentrator ◽  
Cathodic Arc ◽  
The Magnetic Field

The flow, energy distribution and concentrations profiles of Ti ions in cathodic arc are studied by test particle Monte Carlo simulations with considering the mass transfer through the macro-particles filters with inhomogeneous magnetic field. The loss of ions due to their deposition on filter walls was calculated as a function of electric current and number of turns in the coil. The magnetic field concentrator that arises in the bending region of the filters leads to increase the loss of the ions component of cathodic arc. The ions loss up to 80 % of their energy resulted by the paired elastic collisions which correspond to the experimental results. The ion fluxes arriving at the surface of the substrates during planetary rotating of them opposite the evaporators mounted to each other at an angle of 120° characterized by the wide range of mutual overlapping.

Experimental investigation and optimization on field shaper structure parameters in magnetic pulse welding

2021 ◽  
pp. 095440542110148
Author(s):  
Yingzi Chen ◽  
Zhiyuan Yang ◽  
Wenxiong Peng ◽  
Huaiqing Zhang
Keyword(s):  
Magnetic Field ◽  
High Speed ◽  
Light Metal ◽  
Magnetic Pulse ◽  
Cross Sectional ◽  
Magnetic Pulse Welding ◽  
Pulse Welding ◽  
Sectional Shape ◽  
Welding System ◽  
The Magnetic Field

Magnetic pulse welding is a high-speed welding technology, which is suitable for welding light metal materials. In the magnetic pulse welding system, the field shaper can increase the service life of the coil and contribute to concentrating the magnetic field in the welding area. Therefore, optimizing the structure of the field shaper can effectively improve the efficiency of the system. This paper analyzed the influence of cross-sectional shape and inner angle of the field shaper on the ability of concentrating magnetic field via COMSOL software. The structural strength of various field shapers was also analyzed in ABAQUS. Simulation results show that the inner edge of the field shaper directly affects the deformation and welding effect of the tube. So, a new shape of field shaper was proposed and the experimental results prove that the new field shaper has better performance than the conventional field shaper.

scholarly journals No-z Model for Magnetic Fields of Different Astrophysical Objects and Stability of the Solutions

Data ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 4
Author(s):  
Evgeny Mikhailov ◽  
Daniela Boneva ◽  
Maria Pashentseva
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Point Of View ◽  
Accretion Discs ◽  
Wide Range ◽  
Astrophysical Objects ◽  
Alpha Effect ◽  
The Stability ◽  
The Magnetic Field

A wide range of astrophysical objects, such as the Sun, galaxies, stars, planets, accretion discs etc., have large-scale magnetic fields. Their generation is often based on the dynamo mechanism, which is connected with joint action of the alpha-effect and differential rotation. They compete with the turbulent diffusion. If the dynamo is intensive enough, the magnetic field grows, else it decays. The magnetic field evolution is described by Steenbeck—Krause—Raedler equations, which are quite difficult to be solved. So, for different objects, specific two-dimensional models are used. As for thin discs (this shape corresponds to galaxies and accretion discs), usually, no-z approximation is used. Some of the partial derivatives are changed by the algebraic expressions, and the solenoidality condition is taken into account as well. The field generation is restricted by the equipartition value and saturates if the field becomes comparable with it. From the point of view of mathematical physics, they can be characterized as stable points of the equations. The field can come to these values monotonously or have oscillations. It depends on the type of the stability of these points, whether it is a node or focus. Here, we study the stability of such points and give examples for astrophysical applications.

The role of slow magnetostrophic waves in dipole formation in rapidly rotating dynamos

2021 ◽  
Author(s):  
Aditya Varma ◽  
Binod Sreenivasan
Keyword(s):  
Magnetic Field ◽  
Threshold Value ◽  
Dipole Field ◽  
Wave Frequency ◽  
Alfven Wave ◽  
Inertial Waves ◽  
Axial Dipole ◽  
Wide Range ◽  
The Magnetic Field

<p>It is known that the columnar structures in rapidly rotating convection are affected by the magnetic field in ways that enhance their helicity. This may explain the dominance of the axial dipole in rotating dynamos. Dynamo simulations starting from a small seed magnetic field have shown that the growth of the field is accompanied by the excitation of convection in the energy-containing length scales. Here, this process is studied by examining axial wave motions in the growth phase of the dynamo for a wide range of thermal forcing. In the early stages of evolution where the field is weak, fast inertial waves weakly modified by the magnetic field are abundantly present. As the field strength(measured by the ratio of the Alfven wave to the inertial wave frequency) exceeds a threshold value, slow magnetostrophic waves are spontaneously generated. The excitation of the slow waves coincides with the generation of helicity through columnar motion, and is followed by the formation of the axial dipole from a chaotic, multipolar state. In strongly driven convection, the slow wave frequency is attenuated, causing weakening of the axial dipole intensity. Kinematic dynamo simulations at the same parameters, where only fast inertial waves are present, fail to produce the axial dipole field. The dipole field in planetary dynamos may thus be supported by the helicity from slow magnetostrophic waves.</p>

The Earth's Magnetic Field

1950 ◽  
Vol 3 (1) ◽  
pp. 1-9
Author(s):  
Harold Spencer Jones
Keyword(s):  
Magnetic Field ◽  
High Speed ◽  
Spherical Triangle ◽  
Basic Data ◽  
Earth’S Magnetic Field ◽  
Wide Range ◽  
Earth's Magnetic Field ◽  
The Many ◽  
Right Ascension ◽  
Nautical Almanac

The Institute has now completed two years of its existence. The papers which have been read before it during these two years have covered a wide range of subjects and have served to emphasize the many ramifications of the science of navigation. Because of the high speed of modern aircraft, air navigation presents more problems and of greater variety than surface navigation, but even on the problems of surface navigation there has been ample scope for a wide range of discussion. The Institute has taken a prominent part in the discussion of the proposals for the revision of the Abridged Nautical Almanac. It might with some reason have been supposed that there was nothing more to be said on the methods of reducing astro-sights and determining position at sea. The problem is perfectly straightforward and there is a limit to the number of different ways in which the spherical triangle can be solved. But the essential basic data can be presented in a variety of ways, while there are many possible methods of presenting tables for the solution of the spherical triangle. The decision to use Greenwich hour angle instead of right ascension in the Abridged Nautical Almanac has followed its adoption in the Air Almanac; the revised Almanac will have an entirely different format from the present, while the methods of reducing sights must be correspondingly modified.

scholarly journals Relativistic Particle Acceleration in Plerions

1994 ◽  
Vol 142 ◽  
pp. 797-806
Author(s):  
Jonathan Arons ◽  
Marco Tavani
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Shock Waves ◽  
Shock Front ◽  
Heavy Ions ◽  
Surface Brightness ◽  
Crab Nebula ◽  
Electrons And Positrons ◽  
The Crab Nebula ◽  
The Magnetic Field

AbstractWe discuss recent research on the structure and particle acceleration properties of relativistic shock waves in which the magnetic field is transverse to the flow direction in the upstream medium, and whose composition is either pure electrons and positrons or primarily electrons and positrons with an admixture of heavy ions. Particle-in-cell simulation techniques as well as analytic theory have been used to show that such shocks in pure pair plasmas are fully thermalized—the downstream particle spectra are relativistic Maxwellians at the temperature expected from the jump conditions. On the other hand, shocks containing heavy ions which are a minority constituent by number but which carry most of the energy density in the upstream medium do put ~20% of the flow energy into a nonthermal population of pairs downstream, whose distribution in energy space is N(E) ∝ E−2, where N(E)dE is the number of particles with energy between E and E + dE.The mechanism of thermalization and particle acceleration is found to be synchrotron maser activity in the shock front, stimulated by the quasi-coherent gyration of the whole particle population as the plasma flowing into the shock reflects from the magnetic field in the shock front. The synchrotron maser modes radiated by the heavy ions are absorbed by the pairs at their (relativistic) cyclotron frequencies, allowing the maximum energy achievable by the pairs to be γ±m±c2 = mic2γ1/Zi, where γ1 is the Lorentz factor of the upstream flow and Zi, is the atomic number of the ions. The shock’s spatial structure is shown to contain a series of “overshoots” in the magnetic field, regions where the gyrating heavy ions compress the magnetic field to levels in excess of the eventual downstream value.This shock model is applied to an interpretation of the structure of the inner regions of the Crab Nebula, in particular to the “wisps,” surface brightness enhancements near the pulsar. We argue that these surface brightness enhancements are the regions of magnetic overshoot, which appear brighter because the small Larmor radius pairs are compressed and radiate more efficiently in the regions of more intense magnetic field. This interpretation suggests that the structure of the shock terminating the pulsar’s wind in the Crab Nebula is spatially resolved, and allows one to measure γ1, and a number of other properties of the pulsar’s wind. We also discuss applications of the shock theory to the termination shocks of the winds from rotation-powered pulsars embedded in compact binaries. We show that this model adequately accounts for (and indeed predicted) the recently discovered X-ray flux from PSR 1957+20, and we discuss several other applications to other examples of these systems.Subject headings: acceleration of particles — ISM: individual (Crab Nebula) — relativity — shock waves

scholarly journals Study of the Magnetic Field of the Galaxy using Correlation Functions of the Intensity of Synchrotron Background Radio Emission

1996 ◽  
Vol 169 ◽  
pp. 615-616
Author(s):  
V.R. Shoutenkov
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Correlation Functions ◽  
Theoretical Calculations ◽  
Angular Separation ◽  
Field Studies ◽  
Position Angle ◽  
The Galaxy ◽  
Image Position ◽  
The Magnetic Field

The possibility to study magnetic field of the Galaxy calculating correlation or structure functions of synchrotron background radio emission have been known long ago (Kaplan and Pikel'ner (1963); Getmantsev (1958)). But this method had not been as popular as other methods of magnetic field studies. However theoretical calculations made by Chibisov and Ptuskin (1981) showed that correlation functions of intensity of synchrotron background radio emission can give a lot of valuable information about galactic magnetic fields because of the intensity of synchrotron background radio emission depends on H⊥. According to this theory correlation C(θ, φ) and structure S(θ, φ) functions of intensity, as functions of angular separation θ between two lines of sight and position angle φ on the sky between this two lines of sight, can be presented as a sum of isotropic (not dependent from angle φ) and anisotropic parts:

scholarly journals Rapidly Evolving Structures in the Photosphere of the Mira Variable TX Cam

2001 ◽  
Vol 205 ◽  
pp. 252-255 ◽  
Author(s):  
P. J. Diamond ◽  
A. J. Kemball
Keyword(s):  
Magnetic Field ◽  
Gravitational Field ◽  
Shock Waves ◽  
Circumstellar Envelope ◽  
Structural Variations ◽  
Mira Variable ◽  
The Magnetic Field ◽  
Dynamical Mode

44 VLBA observations of the 43 GHz SiO masers in the circumstellar envelope surrounding the Mira variable TX Cam reveal dramatic structural variations over the 80 week stellar cycle. The dominant dynamical mode is one of expansion although other complex motions are visible. The gravitational field of the star does not have a significant effect on the dynamics observed, these are probably governed more by the magnetic field and the effects of the shock waves resulting from the pulsation of the Mira itself.

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