Magnetohydrodynamic Waves in the Solar Corona

The corona of the Sun is a unique environment in which magnetohydrodynamic (MHD) waves, one of the fundamental processes of plasma astrophysics, are open to a direct study. There is striking progress in both observational and theoretical research of MHD wave processes in the corona, with the main recent achievements summarized as follows: ▪ Both periods and wavelengths of the principal MHD modes of coronal plasma structures, such as kink, slow and sausage modes, are confidently resolved. ▪ Scalings of various parameters of detected waves and waveguiding plasma structures allow for the validation of theoretical models. In particular, kink oscillation period scales linearly with the length of the oscillating coronal loop, clearly indicating that they are eigenmodes of the loop. Damping of decaying kink and standing slow oscillations depends on the oscillation amplitudes, demonstrating the importance of nonlinear damping. ▪ The dominant excitation mechanism for decaying kink oscillations is associated with magnetized plasma eruptions. Propagating slow waves are caused by the leakage of chromospheric oscillations. Fast wave trains could be formed by waveguide dispersion. ▪ The knowledge gained in the study of coronal MHD waves provides ground for seismological probing of coronal plasma parameters, such as the Alfvén speed, the magnetic field and its topology, stratification, temperature, fine structuring, polytropic index, and transport coefficients.

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Dispersive MHD waves and alfvenons in charge non-neutral plasmas

Nonlinear Processes in Geophysics ◽

10.5194/npg-15-681-2008 ◽

2008 ◽

Vol 15 (4) ◽

pp. 681-693 ◽

Cited By ~ 3

Author(s):

K. Stasiewicz ◽

J. Ekeberg

Keyword(s):

Soliton Solutions ◽

Theoretical Models ◽

Mhd Waves ◽

Space Plasmas ◽

Charge Effects ◽

Novel Technique ◽

Solitary Structures ◽

Spatial Dimensions ◽

Electric Potentials ◽

Linear And Nonlinear

Abstract. Dispersive properties of linear and nonlinear MHD waves, including shear, kinetic, electron inertial Alfvén, and slow and fast magnetosonic waves are analyzed using both analytical expansions and a novel technique of dispersion diagrams. The analysis is extended to explicitly include space charge effects in non-neutral plasmas. Nonlinear soliton solutions, here called alfvenons, are found to represent either convergent or divergent electric field structures with electric potentials and spatial dimensions similar to those observed by satellites in auroral regions. Similar solitary structures are postulated to be created in the solar corona, where fast alfvenons can provide acceleration of electrons to hundreds of keV during flares. Slow alfvenons driven by chromospheric convection produce positive potentials that can account for the acceleration of solar wind ions to 300–800 km/s. New results are discussed in the context of observations and other theoretical models for nonlinear Alfvén waves in space plasmas.

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Numerical simulations of fast MHD waves in a coronal plasma

Solar Physics ◽

10.1007/bf00627592 ◽

1993 ◽

Vol 144 (2) ◽

pp. 255-266 ◽

Cited By ~ 22

Author(s):

K. Murawski ◽

B. Roberts

Keyword(s):

Numerical Simulations ◽

Coronal Plasma ◽

Mhd Waves

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Investigation on penetration model of shaped charge jet in water

Modern Physics Letters B ◽

10.1142/s0217984915502681 ◽

2016 ◽

Vol 30 (02) ◽

pp. 1550268 ◽

Cited By ~ 1

Author(s):

Jinwei Shi ◽

Xingbai Luo ◽

Jinming Li ◽

Jianwei Jiang

Keyword(s):

Numerical Simulation ◽

Theoretical Model ◽

Model Simulation ◽

Theoretical Models ◽

Theoretical Research ◽

Water Medium ◽

Simulation Results ◽

Jet Penetration ◽

The Impact ◽

Penetration Velocity

To analyze the process of jet penetration in water medium quantitatively, the properties of jet penetration spaced target with water interlayer were studied through test and numerical simulation. Two theoretical models of jet penetration in water were proposed. The theoretical model 1 was established considering the impact of the shock wave, combined with the shock equation Rankine–Hugoniot and the virtual origin calculation method. The theoretical model 2 was obtained by fitting theoretical analysis and numerical simulation results. The effectiveness and universality of the two theoretical models were compared through the numerical simulation results. Both the models can reflect the relationship between the penetration velocity and the penetration distance in water well, and both the deviation and stability of theoretical model 1 are better than 2, the lower penetration velocity, and the larger deviation of the theoretical model 2. Therefore, the theoretical model 1 can reflect the properties of jet penetration in water effectively, and provide the reference of model simulation and theoretical research.

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Generation of Efficient Terahertz Radiation by Relativistic Self-Focusing of A Cosh-Gaussian Laser Beam in A Magnetized Plasma

10.21203/rs.3.rs-1195824/v1 ◽

2021 ◽

Author(s):

Gunjan Purohit ◽

Bineet Gaur ◽

Pradeep Kothiyal ◽

Amita Raizada

Keyword(s):

Laser Beam ◽

Numerical Study ◽

The Self ◽

Magnetized Plasma ◽

Thz Radiation ◽

Gaussian Laser Beam ◽

Plasma Parameters ◽

Gaussian Profile ◽

Self Focusing ◽

Incident Laser Intensity

Abstract This paper presents a scheme for the generation of terahertz (THz) radiation by self-focusing of a cosh-Gaussian laser beam in the magnetized and rippled density plasma, when relativistic nonlinearity is operative. The strong coupling between self-focused laser beam and pre-existing density ripple produces nonlinear current that originates THz radiation. THz radiation is produced by the interaction of the cosh-Gaussian laser beam with electron plasma wave under the appropriate phase matching conditions. Expressions for the beamwidth parameter of cosh-Gaussian laser beam and the electric vector of the THz radiation have been obtained using higher-order paraxial theory and solved numerically. The self-focusing of the cosh-Gaussian laser beam and its effect on the generated THz amplitude have been studied for specific laser and plasma parameters. Numerical study has been performed on various values of the decentered parameter, incident laser intensity, magnetic field, and relative density. The results have also been compared with the paraxial region as well as the Gaussian profile of laser beam. Numerical results suggest that the self-focusing of the cosh-Gaussian laser beam and the amplitude of THz radiation increase in the extended paraxial region compared to the paraxial region. It is also observed that the focusing of the cosh-Gaussian laser beam in the magnetized plasma and the amplitude of the THz radiation increases at higher values of the decentered parameter.

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Understanding core tungsten (W) transport and control in an improved high-performance fully non-inductive discharge on EAST

Nuclear Fusion ◽

10.1088/1741-4326/ac3e3c ◽

2021 ◽

Author(s):

Shengyu Shi ◽

Jiale Chen ◽

Clarisse Bourdelle ◽

Xiang Jian ◽

Tomas Odstrcil ◽

...

Keyword(s):

Density Profile ◽

Turbulent Diffusion ◽

High Performance ◽

Electron Cyclotron Resonance ◽

Transport Coefficients ◽

Linear Instability ◽

Electron Cyclotron Resonance Heating ◽

Plasma Parameters ◽

Turbulent Diffusion Coefficient ◽

Inductive Discharge

Abstract The behavior of heavy/high-Z impurity tungsten (W) in an improved high-performance fully non-inductive discharge on EAST with ITER-like divertor (ILD) is analyzed. It is found that W could be well controlled. The causes of no W accumulation are clarified by analyzing the background plasma parameters and modeling the W transport. It turns out that the electron temperature (T_e) and its gradient are usually high while the toroidal rotation and density peaking of the bulk plasma are small. In this condition, the modeled W turbulent diffusion coefficient is big enough to offset the total turbulent and neoclassical pinch, so that W density profile for zero particle flux will not be very peaked. Combining NEO and TGLF for the W transport coefficient and the impurity transport code STRAHL, not only the core W density profile is predicted but also the radiated information mainly produced by W in the experiment can be closely reconstructed. At last, the physics of controlling W accumulation by electron cyclotron resonance heating (ECRH) is illustrated considering the effects of changed T_e by ECRH on ionization balance and transport of W. It shows that the change of ionization and recombination balance by changed T_e is not enough to explain the experimental observation of W behavior, which should be attributed to the changed W transport. By comparing the W transport coefficients in two kinds of plasmas with different T_e profiles, it is shown that high T_e and its gradient play a key role to generate large turbulent diffusion through increasing the growth rate of linear instability so that W accumulation is prevented.

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Utilizing Emotions for Ethical Decision Making in Leadership

Advances in Business Strategy and Competitive Advantage - International Business Ethics and Growth Opportunities ◽

10.4018/978-1-4666-7419-6.ch008 ◽

2015 ◽

pp. 158-175

Author(s):

Jennifer A. Griffith ◽

Thomas A. Zeni ◽

Genevieve Johnson

Keyword(s):

Decision Making ◽

Ethical Decision ◽

Ethical Decision Making ◽

Theoretical Models ◽

Theoretical Research ◽

Decision Making Process ◽

Organizational Leaders ◽

Emotional Component

Modern organizational leaders must rise to the challenge of making both ethically sound decisions as well as traditional fiscal decisions in order to remain competitive in today's marketplace. It is critical for leaders to be mindful of how emotions may assist or hinder them throughout the ethical decision-making process. Attempting to ignore the emotional component of ethical decision making or pretending that emotions do not exert influence on decisions is foolhardy and disregards both empirical and theoretical research suggesting otherwise. The challenge for leaders is how to best incorporate emotion into ethical decision making. This chapter examines several theoretical models of emotion and ethical decision making, applies theoretical and empirical findings to explain how two common emotions—anger and anxiety—impact ethical decision making, and provides recommendations for leaders seeking to improve ethical decision-making outcomes.

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Collisional transport for a superthermal ion species in magnetized plasma

Journal of Plasma Physics ◽

10.1017/s0022377800011806 ◽

1986 ◽

Vol 36 (3) ◽

pp. 313-328 ◽

Cited By ~ 3

Author(s):

F. Cozzani ◽

W. Horton

Keyword(s):

Kinetic Equation ◽

Transport Theory ◽

A Priori ◽

Transport Coefficients ◽

Kinetic Equations ◽

High Energy ◽

Magnetized Plasma ◽

Fractional Density ◽

Background Ions ◽

Ion Species

The transport theory of a high-energy ion species injected isotropically in a magnetized plasma is considered for arbitrary ratios of the high-energy ion cyclotron frequency to the collisional slowing down time. The assumptions of (i) low fractional density of the high-energy species and (ii) average ion speed faster than the thermal ions and slower than the electrons are used to decouple the kinetic equation for the high-energy species from the kinetic equations for background ions and electrons. The kinetic equation is solved by a Chapman–Enskog expansion in the strength of the gradients; an equation for the first correction to the lowest-order distribution function is obtained without scaling a priori the collision frequency with respect to the gyrofrequency. Various transport coefficients are explicitly calculated for the two cases of a weakly and a strongly magnetized plasma.

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MHD Seismology of the Solar Corona with SOHO and TRACE

Symposium - International Astronomical Union ◽

10.1017/s0074180900219517 ◽

2001 ◽

Vol 203 ◽

pp. 353-355 ◽

Cited By ~ 9

Author(s):

V. M. Nakariakov

Keyword(s):

Magnetic Field ◽

Solar Corona ◽

Decay Time ◽

Transport Coefficients ◽

Mhd Waves ◽

The Mean ◽

Temporal And Spatial ◽

Wave Phenomena ◽

The Magnetic Field ◽

Imaging Telescopes

Recent discoveries of MHD wave motions in the solar corona done with EUV imaging telescopes onboard SOHO and TRACE provide an observational basis for the MHD seismology of the corona. Measuring the properties of MHD waves and oscillations (periods, wavelengths, amplitudes, temporal and spatial signatures), combined with theoretical modeling of the wave phenomena, allow us to determine values of the mean parameters of the corona (the magnetic field strength, transport coefficients, etc.). As an example, we consider post-flare decaying oscillations of loops, observed with TRACE (14th July 1998 at 12:55 UT). An analysis of the oscillations shows that they are quasi-harmonic, with a period of about 265 s, and quickly decaying with the decay time of about 14.5 min. The period of oscillations allows us to determine the Alfvén speed in the oscillating loop about 770 km/s. This value can be used for deduction of the value of the magnetic field in the loop (giving 10-30 G). The decay time, in the assumption that the decay is caused by viscous (or resistive) dissipation, gives us the Reynolds number of 105.3-6.1 (or the Lundquist number of 105.0-5.8).

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