scholarly journals Wave Energy Dissipation in the Solar Atmosphere

1990 ◽  
Vol 142 ◽  
pp. 266-267
Author(s):  
Zhou Aihua
Keyword(s):  
Magnetic Field ◽  
Heat Conduction ◽  
Transition Region ◽  
Wave Dissipation ◽  
Wave Energy Dissipation ◽  
Wave Heating ◽  
Order Of Magnitude ◽  
Lower Temperature ◽  
The Magnetic Field ◽  
Field Wave

There are two regions of rapid dissipation when Alfvén waves propagate from the transition region to the corona. They occur respectively in a range of several hundred kilometers above the base of the transition region and in the corona at about 1-3Ro. The heating of the atmosphere by wave dissipation could be one order of magnitude larger than heat conduction in the coronal part with a lower temperature and density and stronger magnetic field. Wave heating could also become more important when the magnetic field divergence becomes stronger.

scholarly journals Alfvén Waves in Dusty Interstellar Clouds

1997 ◽  
Vol 14 (2) ◽  
pp. 170-178 ◽  
Author(s):  
N. F. Cramer ◽  
S. V. Vladimirov
Keyword(s):  
Magnetic Field ◽  
Negative Charge ◽  
Alfven Waves ◽  
Dust Particles ◽  
Alfvén Waves ◽  
Interstellar Clouds ◽  
General Dispersion ◽  
The Right ◽  
The Magnetic Field ◽  
Field Wave

AbstractDust particles in a plasma can be higWy charged, and can carry a proportion of the negative charge of the plasma. Even if this proportion is quite small, as in interstellar dusty clouds, it can have a large effect on hydromagnetic Alfvén waves propagating at frequencies well below the ion–cyclotron frequency. In particular, the right-hand circularly polarised mode experiences a cutoff due to the presence of the dust. We generalise previous work on Alfvén waves in dusty interstellar plasmas by considering the general dispersion relation for waves propagating at an arbitrary angle with respect to the magnetic field. Wave energy propagating at oblique angles to the magnetic field in an increasing density gradient can be very efficiently damped by the Alfvén resonance absorption process in a dusty plasma, and we consider this damping mechanism for waves in interstellar clouds.

End effects in the magnetic field of free electron lasers with sheet electron beams

1990 ◽  
Vol 68 (11) ◽  
pp. 1227-1236
Author(s):  
G. Pocobelli
Keyword(s):  
Magnetic Field ◽  
Free Electron ◽  
Electron Beams ◽  
Field Measurements ◽  
End Effects ◽  
Direction Parallel ◽  
Additional Degree ◽  
Order Of Magnitude ◽  
Three Space ◽  
The Magnetic Field

We calculate the magnetic field of a free-electron-laser's wiggler of a recent design (Granatstein et al. Appl. Phys. Lett. 74, 643 (1985)) using sheet electron beams. We did not assume periodic boundary conditions, as was done in their work, and we obtained analytical expressions in two of the three space variables. We found various irregularities in the field behavior that were dependent on the size of the wiggler in the x direction (parallel to the beam's wide size), and that increased up to a width an order of magnitude greater than the height of the beam channel. These irregularities had been observed in field measurements. A method consisting of making the end magnets thinner worked effectively to reduce the irregularities. We also studied a similar magnetic configuration with free and independent currents and no magnets, and added the additional degree of freedom of programming the currents to further reduce the irregularities.

ON THE THEORY OF ALLOY SOLIDIFICATION IN A MAGNETIC FIELD

1964 ◽  
Vol 42 (11) ◽  
pp. 2238-2258 ◽  
Author(s):  
W. V. Youdelis ◽  
D. R. Colton ◽  
J. Cahoon
Keyword(s):  
Magnetic Field ◽  
Diffusion Rate ◽  
Irreversible Thermodynamic ◽  
Chill Face ◽  
Convective Mixing ◽  
System A ◽  
Aluminium Copper ◽  
Order Of Magnitude ◽  
Chill Cast ◽  
The Magnetic Field

The degree of segregation in unidirectionally solidified ingots, chill-cast in magnetic fields up to 34 kilo-oersteds, has been determined for alloys of the aluminium–copper and bismuth–antimony systems. It is found that the chill-face segregation in aluminium–copper ingots is increased approximately 50% above the no-field ingots for a 34-kilo-oersted field. The effect is independent of field direction. A 13-kilo-oersted field decreases the chill-face segregation by 60% in ingots of the bismuth (rich) – antimony system. A theory based on the diffusion inhibition effect of the magnetic field (previously reported) is presented to explain the segregation change. By applying irreversible thermodynamic principles, it is shown that the segregation changes in the field-solidified ingots are a manifestation of the decreased entropy production of the diffusion, convective mixing, and viscous flow processes of solidification in a magnetic field. For the aluminium–copper ingots there is order-of-magnitude agreement between the observed segregation change and the decreased diffusion rate in the magnetic field.

Effect of non-uniform magnetic field on two ion species plasma-wall transition

2021 ◽  
Author(s):  
Atit Deuja ◽  
Suresh Basnet ◽  
Raju Khanal
Keyword(s):  
Magnetic Field ◽  
Transition Region ◽  
Uniform Magnetic Field ◽  
Boltzmann Distribution ◽  
Magnetized Plasma ◽  
Magnetic Flux Density ◽  
Sheath Region ◽  
Average Value ◽  
Ion Species ◽  
The Magnetic Field

Abstract Fluid theory has been employed to investigate the magnetized plasma-wall transition properties for two ion species plasmas with a uniform background of neutral gas density in the presence of an external magnetic field. The external applied magnetic field is parallel to the surface and its magnitude varies in the direction perpendicular to the surface. The governing equations of ion and electron fluids include ionization and collision with neutral atoms. A comparative study of transition parameters for non-uniform and uniform magnetic fields is performed at equal values of the magnetic flux density at $x = 0$. This study shows that the sheath region shrinks for the non-uniform magnetic field case, essentially in reason of the lower value of the average magnetic field intensity in the plasma-wall transition region. We introduce a figure of merit to quantify the non-uniformity of the magnetic field $(B_{\mathrm{max}}-B_{\mathrm{min}})/B_{\mathrm{max}}$, and show that for its value 0.21 it is possible to model the plasma-wall transition region considering the magnetic field as uniform and equal to its average value. Furthermore, we find that the density distribution of electrons close to the surface deviates from the Boltzmann distribution due to the influence of a strong magnetic field.

scholarly journals Disentangling flows in the solar transition region

2018 ◽  
Vol 614 ◽  
pp. A110 ◽  
Author(s):  
P. Zacharias ◽  
V. H. Hansteen ◽  
J. Leenaarts ◽  
M. Carlsson ◽  
B. V. Gudiksen
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Transition Region ◽  
Magnetic Field Line ◽  
Spectral Lines ◽  
Continuous Heating ◽  
Solar Transition Region ◽  
Solar Transition ◽  
Energy Flows ◽  
The Magnetic Field

Context. The measured average velocities in solar and stellar spectral lines formed at transition region temperatures have been difficult to interpret. The dominant redshifts observed in the lower transition region naturally leads to the question of how the upper layers of the solar (and stellar) atmosphere can be maintained. Likewise, no ready explanation has been made for the average blueshifts often found in upper transition region lines. However, realistic three-dimensional radiation magnetohydrodynamics (3D rMHD) models of the solar atmosphere are able to reproduce the observed dominant line shifts and may thus hold the key to resolve these issues. Aims. These new 3D rMHD simulations aim to shed light on how mass flows between the chromosphere and corona and on how the coronal mass is maintained. These simulations give new insights into the coupling of various atmospheric layers and the origin of Doppler shifts in the solar transition region and corona. Methods. The passive tracer particles, so-called corks, allow the tracking of parcels of plasma over time and thus the study of changes in plasma temperature and velocity not only locally, but also in a co-moving frame. By following the trajectories of the corks, we can investigate mass and energy flows and understand the composition of the observed velocities. Results. Our findings show that most of the transition region mass is cooling. The preponderance of transition region redshifts in the model can be explained by the higher percentage of downflowing mass in the lower and middle transition region. The average upflows in the upper transition region can be explained by a combination of both stronger upflows than downflows and a higher percentage of upflowing mass. The most common combination at lower and middle transition region temperatures are corks that are cooling and traveling downward. For these corks, a strong correlation between the pressure gradient along the magnetic field line and the velocity along the magnetic field line has been observed, indicating a formation mechanism that is related to downward propagating pressure disturbances. Corks at upper transition region temperatures are subject to a rather slow and highly variable but continuous heating process. Conclusions. Corks are shown to be an essential tool in 3D rMHD models in order to study mass and energy flows. We have shown that most transition region plasma is cooling after having been heated slowly to upper transition region temperatures several minutes before. Downward propagating pressure disturbances are identified as one of the main mechanisms responsible for the observed redshifts at transition region temperatures.

STRUCTURES IN A MAGNETIC SUSPENSION SUBJECTED TO UNIDIRECTIONAL AND ROTATING FIELD

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2279-2285 ◽  
Author(s):  
P. CARLETTO ◽  
G. BOSSIS ◽  
A. CEBERS
Keyword(s):  
Magnetic Field ◽  
Surface Tension ◽  
Thermodynamic Model ◽  
Colloidal Particles ◽  
Average Distance ◽  
Characteristic Size ◽  
Magnetic Suspension ◽  
Order Of Magnitude ◽  
The Magnetic Field ◽  
Rotating Field

Field induced structures are studied inside suspensions of magnetic colloidal particles of micronic size. We have characterized the average distance between aggregates in a thin cell with the magnetic field perpendicular to the plane and also in the presence of a rotating field with the plane of rotation perpendicular to the plane of the cell. The characteristic size of the mesostructure is predicted on the basis of a thermodynamic model. The theory well predicts the experimental results in the uniaxial case but not in the case of ae rotating field; in this last case, the surface tension which is needed to have a good fit is far too low compared to its expected order of magnitude. When the field is uniaxial and sinusoidal we have found a collective instability where all the aggregates are rotating simultaneously in a chaotic way.

scholarly journals Two-dimensional nonlinear travelling waves in magnetohydrodynamic channel flow

2014 ◽  
Vol 760 ◽  
pp. 387-406 ◽  
Author(s):  
Jonathan Hagan ◽  
Jānis Priede
Keyword(s):  
Magnetic Field ◽  
Linear Stability ◽  
Channel Flow ◽  
Travelling Waves ◽  
Transverse Magnetic ◽  
Travelling Wave ◽  
Linear Stability Theory ◽  
Two Dimensional ◽  
Order Of Magnitude ◽  
The Magnetic Field

AbstractThis study is concerned with the stability of a flow of viscous conducting liquid driven by a pressure gradient in the channel between two parallel walls subject to a transverse magnetic field. Although the magnetic field has a strong stabilizing effect, this flow, similarly to its hydrodynamic counterpart – plane Poiseuille flow – is known to become turbulent significantly below the threshold predicted by linear stability theory. We investigate the effect of the magnetic field on two-dimensional nonlinear travelling-wave states which are found at substantially subcritical Reynolds numbers starting from $\mathit{Re}_{n}=2939$ without the magnetic field and from $\mathit{Re}_{n}\sim 6.50\times 10^{3}\mathit{Ha}$ in a sufficiently strong magnetic field defined by the Hartmann number $\mathit{Ha}$. Although the latter value is a factor of seven lower than the linear stability threshold $\mathit{Re}_{l}\sim 4.83\times 10^{4}\mathit{Ha}$, it is still more than an order of magnitude higher than the experimentally observed value for the onset of turbulence in magnetohydrodynamic (MHD) channel flow.

scholarly journals Observation of Fractal Conductance Fluctuations over Three Orders of Magnitude

1999 ◽  
Vol 52 (5) ◽  
pp. 887 ◽  
Author(s):  
R. P. Taylor ◽  
A. P. Micolich ◽  
R. Newbury ◽  
T. M. Fromhold ◽  
C. R. Tench
Keyword(s):  
Magnetic Field ◽  
Transport Properties ◽  
Field Range ◽  
Magnetic Field Range ◽  
Physical Conditions ◽  
Fractal Behaviour ◽  
Conductance Fluctuations ◽  
Order Of Magnitude ◽  
The Magnetic Field

Fractal magneto-transport properties of mesoscopic semiconductor billiards are highly topical. In these studies, the magnetic field range over which fractal behaviour can be observed is crucial. Previous observations have been limited to approximately one order of magnitude. We present fractal conductance fluctuations observed over three orders of magnitude and discuss the physical conditions required to extend this range.

A Dynamo Model for Magnetic Stars with Long Periods

1976 ◽  
Vol 32 ◽  
pp. 39-42
Author(s):  
M. Schüssler
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Convection Zone ◽  
Dynamo Model ◽  
Magnetic Stars ◽  
Order Of Magnitude ◽  
Linear Effects ◽  
The Right ◽  
Right Order ◽  
The Magnetic Field

SummaryA α - effect dynamo model is presented which can be relevant for the group of magnetic stars.with observed periods between 1 y and 72 ys. The model is based on an axisymmetric α2- dynamo including non-linear effects due to the “cut off α- effect”; no differential rotation is taken into account. There are oscilliations of the magnetic field with periods in the right order of magnitude under the assumption of an outer convection zone between R ≥ r ≥.5 R ….7R. In the sense of this model therefore these stars should be young objects passing from their Hayashi track down to the main sequence.

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