scholarly journals α-Stability Analysis of Hydromagnetic Instabilities in Stars with Toroidal Magnetic Fields

1980 ◽  
Vol 58 ◽  
pp. 667-672
Author(s):  
M. Goossens ◽  
D. Biront
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Stability Analysis ◽  
Magnetic Fields ◽  
Sufficient Conditions ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Toroidal Magnetic Field ◽  
Displacement Fields ◽  
Necessary And Sufficient

Abstractα-stability analysis is used to investigate the adiabatic stability of a star containing an axisymmetric toroidal magnetic field. Necessary and sufficient conditions for α-stability are derived. Special attention is devoted to the typical hydromagnetic instabilities that can be introduced by a weak toroidal magnetic field in a star that is stably stratified in the absence of any magnetic field. An expression for the maximum growth rate of instability is derived and the basic properties of the displacement fields associated with the instabilities are indicated.

scholarly journals Are the photospheric sunspots magnetically force-free in nature?

2010 ◽  
Vol 6 (S273) ◽  
pp. 333-337 ◽  
Author(s):  
Sanjiv Kumar Tiwari
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Magnetic Energy ◽  
Sufficient Conditions ◽  
Field Measurements ◽  
Magnetic Behaviour ◽  
Optical Telescope ◽  
Energy Gradient ◽  
Necessary And Sufficient

AbstractIn a force-free magnetic field, there is no interaction of field and the plasma in the surrounding atmosphere i.e., electric currents are aligned with the magnetic field, giving rise to zero Lorentz force. The computation of many magnetic parameters like magnetic energy, gradient of twist of sunspot magnetic fields (computed from the force-free parameter α), including any kind of extrapolations heavily hinge on the force-free approximation of the photospheric magnetic fields. The force-free magnetic behaviour of the photospheric sunspot fields has been examined by Metcalf et al. (1995) and Moon et al. (2002) ending with inconsistent results. Metcalf et al. (1995) concluded that the photospheric magnetic fields are far from the force-free nature whereas Moon et al. (2002) found the that the photospheric magnetic fields are not so far from the force-free nature as conventionally regarded. The accurate photospheric vector field measurements with high resolution are needed to examine the force-free nature of sunspots. We use high resolution vector magnetograms obtained from the Solar Optical Telescope/Spectro-Polarimeter (SOT/SP) aboard Hinode to inspect the force-free behaviour of the photospheric sunspot magnetic fields. Both the necessary and sufficient conditions for force-freeness are examined by checking global as well as as local nature of sunspot magnetic fields. We find that the sunspot magnetic fields are very close to the force-free approximation, although they are not completely force-free on the photosphere.

The Influence of Magnetic Fields by a Melting Rate of Wire for Arc Surfacing under Flux

2013 ◽  
Vol 379 ◽  
pp. 178-182 ◽  
Author(s):  
D.G. Nosov ◽  
V.V. Maltsev
Keyword(s):  
Growth Rate ◽  
Magnetic Fields ◽  
Maximum Growth ◽  
Melting Rate ◽  
Maximum Growth Rate ◽  
Electric Arc ◽  
Filler Materials

As a result of the study the degree of influence of external magnetic fields on the efficiency of fusion surfacing wire for electric arc surfacing under flux conditions have been established regime for different combinations of basic and filler materials (ferromagnetic and nonmagnetic) at which the maximum growth rate of melting.

Longitudinal waves in a perpendicular collisionless plasma shock: I. Cold ions

1970 ◽  
Vol 4 (4) ◽  
pp. 739-751 ◽  
Author(s):  
S. Peter Gary ◽  
J. J. Sanderson
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Collisionless Plasma ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Wave Number ◽  
Zero Magnetic Field ◽  
Linear Dispersion ◽  
Electrostatic Waves ◽  
Cold Ions

This paper considers electrostatic waves in a Vlasov plasma of unmagnetized ions and magnetized, Maxwellian electrons. The linear dispersion relation is derived for waves in a perpendicular shock such that the most important sources of instability are the E × B and ∇B electron drifts. For the case of cold ions, propagation perpendicular to the applied magnetic field, and the E × B drift alone, a numerical analysis of frequency vs. wave-number is presented. The effects of the ∇B drift are also considered, and it is shown that the maximum growth rate can be larger than the maximum growth rate for the zero magnetic field ion acoustic instabifity under comparable conditions.

Kelvin–Helmholtz instability under horizontal rotation and magnetic fields

1998 ◽  
Vol 59 (2) ◽  
pp. 193-209
Author(s):  
L. A. DÁVALOS-OROZCO
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Fluid Layer ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Density Stratification ◽  
Velocity Shear ◽  
Sufficient Condition ◽  
Horizontal Shear ◽  
Helmholtz Instability

The author's previous work on the Rayleigh–Taylor instability is extended to the Kelvin–Helmholtz instability, and the maximum growth rate of a perturbation and an estimate of its upper bound is obtained for an infinite fluid layer under horizontal rotation where the density, horizontal velocity (shear) and magnetic field are continuously stratified in the direction of gravity. Conclusions are drawn about the possibility of stability for some directions of propagation of the perturbation, even in the case of unstably stratified density. It is also shown that the new terms that appear owing to the interaction of the horizontal shear flow, horizontal rotation and stratified magnetic field increase the range of values that contribute to the estimate of the maximum growth rate compared with previous work. Furthermore, a generalization of the sufficient condition for stability under horizontal rotation alone obtained by Johnson is calculated in the presence of density stratification. A new method is also given to obtain a sufficient condition for stability when a magnetic field is present in addition to rotation and density stratification.

scholarly journals Brillouin-shifted third-harmonic backscattering of laser in a magnetized plasma

2015 ◽  
Vol 33 (1) ◽  
pp. 97-102 ◽  
Author(s):  
Alireza Paknezhad
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Static Magnetic Field ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Magnetized Plasma ◽  
Third Harmonic ◽  
Coupled Equations ◽  
Relativistic Mass ◽  
Weakly Coupled

AbstractThird-harmonic Brillouin backscattering (3HBBS) instability is investigated in the interaction of a picosecond extraordinary laser pulse with a homogeneous transversely magnetized underdense plasma. Nonlinear coupled equations that describe the instability are derived and solved for a weakly coupled regime to find the maximum growth rate. The nonlinearity arises through the combined effect of relativistic mass increase, static magnetic field, and ponderomotive acceleration of plasma electrons. The growth rate is found to decrease as the static magnetic field increases. It also increases by increasing both plasma density and laser intensity. It is also established that the growth rate of 3HBBS instability in a magnetized plasma is lower than that of fundamental Brillouin backscattering instability.

Filamentation of a laser beam in a strongly ionized magnetoplasma

1978 ◽  
Vol 19 (1) ◽  
pp. 55-61 ◽  
Author(s):  
L. A. Pitale
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Laser Beam ◽  
Spatial Scale ◽  
Large Scale ◽  
Maximum Growth ◽  
Mean Free Path ◽  
Maximum Growth Rate ◽  
Main Beam ◽  
Small Scale

On a time-scale of the order of the energy relaxation time, a high power laser beam, propagating in a strongly ionized magnetoplasma is shown to be unstable for small scale fluctuations. In the domain r0 < [mi/m]½ λm. v2/[ω2c + v2] (r0, λm, v, ωc, and m being respectively the spatial scale of the perturbation, electron mean free path, collision frequency, cyclotron frequency and mass and mi being the ion mass) the main loss of excess electron energy is due to thermal conduction; in the other limit collisional loss dominates. It is shown that for small scale fluctuations the growth rate increases with (i) increasing magnetic field and (ii) increasing r0. For large scale fluctuations the magnetic field does not show any effect; the growth rate, however, diminishes with increasing spatial scale. A maximum growth rate is obtained both for some optimum value of scale length and for intensity of the main beam.

Stability of cylindrical rotating plasmas to axisymmetric electrostatic perturbations

1977 ◽  
Vol 17 (3) ◽  
pp. 409-418 ◽  
Author(s):  
E. M. Barston
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Maximum Principle ◽  
Axial Magnetic Field ◽  
Sufficient Conditions ◽  
Maximal Growth ◽  
Unstable System ◽  
Rotating Plasmas ◽  
Maximal Growth Rate ◽  
Necessary And Sufficient

Necessary and sufficient conditions for the exponential stability of an N-component, warm or cold, rotating cylindrical plasma to axisymmetric electrostatic perturbations are obtained. The plasma is immersed in an axial magnetic field B0(r), where r is the radial co-ordinate, and the equilibrium quantities are permitted to be arbitrary functions of r consistent with the 0-order equations. The maximal growth rate of an unstable system is shown to be determined by a maximum principle.

A note on growth curves of rabbit lines selected on growth rate or litter size

1993 ◽  
Vol 57 (2) ◽  
pp. 332-334 ◽  
Author(s):  
A. Blasco ◽  
E. Gómez
Keyword(s):  
Growth Rate ◽  
Litter Size ◽  
Growth Curves ◽  
Live Weight ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Standard Errors ◽  
Adult Weight ◽  
Weight Growth ◽  
Using Data

Two synthetic lines of rabbits were used in the experiment. Line V, selected on litter size, and line R, selected on growth rate. Ninety-six animals were randomly collected from 48 litters, taking a male and a female each time. Richards and Gompertz growth curves were fitted. Sexual dimorphism appeared in the line V but not in the R. Values for b and k were similar in all curves. Maximum growth rate took place in weeks 7 to 8. A break due to weaning could be observed in weeks 4 to 5. Although there is a remarkable similarity of the values of all the parameters using data from the first 20 weeks only, the higher standard errors on adult weight would make 30 weeks the preferable time to take data for live-weight growth curves.

Reassessment of Maximum Growth Rates for C3 and C4 Crops

1978 ◽  
Vol 14 (1) ◽  
pp. 1-5 ◽  
Author(s):  
J. L. Monteith
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Growing Season ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Crop Growth ◽  
Close Inspection ◽  
Similar Difference ◽  
Photosynthetic Efficiencies

SUMMARYFigures for maximum crop growth rates, reviewed by Gifford (1974), suggest that the productivity of C3 and C4 species is almost indistinguishable. However, close inspection of these figures at source and correspondence with several authors revealed a number of errors. When all unreliable figures were discarded, the maximum growth rate for C3 stands fell in the range 34–39 g m−2 d−1 compared with 50–54 g m−2 d−1 for C4 stands. Maximum growth rates averaged over the whole growing season showed a similar difference: 13 g m−2 d−1 for C3 and 22 g m−2 d−1 for C4. These figures correspond to photosynthetic efficiencies of approximately 1·4 and 2·0%.

Plasma instabilities driven by pickup ions of ring-beam velocity distributions in the outer heliosheath 

2021 ◽  
Author(s):  
Ameneh Mousavi ◽  
Kaijun Liu ◽  
Sina Sadeghzadeh
Keyword(s):  
Magnetic Field ◽  
Maximum Growth ◽  
Dispersion Analysis ◽  
Maximum Growth Rate ◽  
Injection Velocity ◽  
Plasma Instabilities ◽  
Pickup Ions ◽  
Beam Velocity ◽  
Background Magnetic Field ◽  
Hybrid Simulations

&lt;p&gt;&lt;span&gt;The stability of the pickup ions in the outer heliosheath has been studied by many researchers because of its relevance to the energetic neutral atom (ENA) ribbon observed by the Interstellar Boundary EXplorer. However, previous studies are primarily limited to pickup ions of near &lt;/span&gt;&lt;span&gt;90&amp;#176; &lt;/span&gt;&lt;span&gt;pickup angles, the angle between the pickup ion injection velocity and the background, local interstellar magnetic field. Investigations on pickup ions of smaller pickup angles are still lacking. In this paper, linear kinetic dispersion analysis and hybrid simulations are carried out to examine the plasma instabilities driven by pickup ions of ring-beam velocity distributions at various pickup angles between zero and &lt;/span&gt;&lt;span&gt;90&amp;#176;&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Parallel propagating waves are studied in the parameter regime where the parallel thermal spread of the pickup ions falls into the Alfv&amp;#233;n cyclotron stability gap. &lt;/span&gt;&lt;span&gt;The linear analysis results and hybrid simulations both show that the fastest growing modes are the right-hand helicity waves propagating in the direction of the background magnetic field, and the maximum growth rate occurs at the pickup angle of &lt;/span&gt;&lt;span&gt;82&amp;#176;&lt;/span&gt;&lt;span&gt;. The simulation results further reveal that the saturation level of the fluctuating magnetic fields for pickup angles below &lt;/span&gt;&lt;span&gt;45&amp;#176; &lt;/span&gt;&lt;span&gt;is higher than that for pickup angles above &lt;/span&gt;&lt;span&gt;45&amp;#176;&lt;/span&gt;&lt;span&gt;. So, the scattering of pickup ions at near zero pickup angles is likely more pronounced than that at near &lt;/span&gt;&lt;span&gt;90&amp;#176; &lt;/span&gt;&lt;span&gt;pickup angles&lt;/span&gt; .&lt;/p&gt;

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