scholarly journals Can Resistive Kink Instabilities Drive Simple Loop Flares?

1989 ◽  
Vol 104 (2) ◽  
pp. 305-308
Author(s):  
M. Velli ◽  
G. Emaudi ◽  
A.W. Hood
Keyword(s):  
Magnetic Field ◽  
Boundary Conditions ◽  
Growth Rates ◽  
Axial Magnetic Field ◽  
Small Region ◽  
Coronal Loops ◽  
Simple Loop ◽  
Cylindrically Symmetric ◽  
Line Tying ◽  
Kink Instability

SummaryA detailed analysis of the kink instability in finite length (inertially line-tied), cylindrically symmetric coronal loops is presented. The correct line-tying boundary conditions within the framework of ideal and resistive magnctohydrodynamics are discussed, and the growth rates of unstable modes and corresponding eigenfunctions are calculated. Resistive kink modes are found to be unstable in configurations where the axial magnetic field undergoes an inversion, resistive effects being confined to a small region around the loop vertex.

Effects of repeated interactions and correlational disintegration on kinetic and transport properties of a non-neutral plasma in strong fields

1990 ◽  
Vol 44 (1) ◽  
pp. 167-190 ◽  
Author(s):  
Alf H. Øien
Keyword(s):  
Magnetic Field ◽  
Particle Transport ◽  
Axial Magnetic Field ◽  
Debye Length ◽  
Electron Plasma ◽  
Larmor Radius ◽  
Equilibration Time ◽  
Cylindrically Symmetric ◽  
Electric Potentials ◽  
Good Agreement

Collisions in a cylindrically symmetric non-neutral (electron) plasma, where the Larmor radius is much smaller than the Debye length, and the consequent particle transport, are studied. The plasma is confined radially by a strong axial magnetic field and axially by electric potentials. Hence two particles may interact repeatedly. Eventually they drift too far away from each other poloidally to interact any more, owing to shear in the E × B drift. The consequent build-up of correlation is limited by correlational disintegration due to collisions with ‘third particles’ between the repeated interactions. A kinetic equation including these effects is derived, and the cross-field particle transport along the density gradient is found. An associated equilibration time is shown to scale as B and to be in good agreement with the experimentally obtained values of Briscoli, Malmberg and Fine.

THE STAEILITY OF COUETTE FLOW IN AN AXIAL MAGNETIC FIELD

1958 ◽  
Vol 36 (11) ◽  
pp. 1509-1525 ◽  
Author(s):  
E. R. Niblett
Keyword(s):  
Magnetic Field ◽  
Boundary Conditions ◽  
Theoretical Prediction ◽  
Viscous Flow ◽  
Rotation Speed ◽  
Axial Magnetic Field ◽  
Radioactive Isotopes ◽  
Electrically Conducting ◽  
Electrically Conducting Fluid ◽  
The Stability

Chandrasekhar's theory of the stability of viscous flow of an electrically conducting fluid between coaxial rotating cylinders with perfectly conducting walls is extended to include the case of non-conducting walls, and it is found that their effect is to reduce the critical Taylor numbers and increase the wavelength of the instability patterns by considerable amounts. An experiment designed to measure the values of magnetic field and rotation speed at the onset of instability in mercury between perspex cylinders is described. The radioactive isotopes Hg197 and Hg203 were used to trace the flow. The results support the theoretical prediction that the boundary conditions can have a large effect on the motion.

ONSET OF INSTABILITY IN HYDROMAGNETIC COUETTE FLOW

2004 ◽  
Vol 02 (02) ◽  
pp. 145-159 ◽  
Author(s):  
ISOM H. HERRON
Keyword(s):  
Magnetic Field ◽  
Prandtl Number ◽  
Boundary Conditions ◽  
Viscous Flow ◽  
Couette Flow ◽  
Axial Magnetic Field ◽  
Narrow Gap ◽  
Rotating Cylinders ◽  
Magnetic Prandtl Number ◽  
The Stability

The stability of viscous flow between rotating cylinders in the presence of a constant axial magnetic field is considered. The boundary conditions for general conductivities are examined. It is proved that the Principle of Exchange of Stabilities holds at zero magnetic Prandtl number, for all Chandrasekhar numbers, when the cylinders rotate in the same direction, the circulation decreases outwards, and the cylinders have insulating walls. The result holds for both the finite gap and the narrow gap approximation.

Experimentelle Untersuchung der Rayleigh-Taylor-Instabilität eines rotierenden Wasserstoff-Lichtbogens im axialen Magnetfeld

1969 ◽  
Vol 24 (8) ◽  
pp. 1249-1258
Author(s):  
H Döbele
Keyword(s):  
Magnetic Field ◽  
Light Intensity ◽  
Growth Rates ◽  
Axial Magnetic Field ◽  
Rotational Velocity ◽  
Arc Plasma ◽  
Hollow Anode ◽  
Dissipative Effects ◽  
Periodic Fluctuations ◽  
Experimentelle Untersuchung

Abstract A hydrogen arc with a hollow anode in an axial magnetic field is subjected to Rayleigh-Taylor instabilities as a result of rotation due to the radial current components at the anode. These instabilities take the form of periodic fluctuations in the light intensity emitted from the boundary regions of the arc. The modes m = 4 to m = 7 which occur in succession with increasing magnetic field are identified by measuring the signal phases in end-on observation of the arc. The rotational velocity of the arc plasma is determined spectroscopically and comparison is made with the non-dissipative MHD theory, which yields growth rates ∼ .The deviations from this theory that were observed in this experiment are ascribed to dissipative effects.

Zur Rayleigh-Taylor-Instabilität eines rotierenden Wasserstofflichtbogens im axialen Magnetfeld

1970 ◽  
Vol 25 (2) ◽  
pp. 273-282 ◽  
Author(s):  
H. F. Döbele
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Heat Conduction ◽  
Dispersion Relation ◽  
Electrical Conduction ◽  
Growth Rates ◽  
Plasma Column ◽  
Qualitative Agreement ◽  
Axial Magnetic Field ◽  
Rayleigh Taylor Instability

Abstract The Rayleigh-Taylor instability of a rotating hydrogen arc in an axial magnetic field is investigated with allowance for electrical conduction, heat conduction and viscosity. The r-depending part of the perturbation was assumed to be in the form of a half-period of a standing wave. The corresponding dispersion relation is derived in the WKB-approximation and is solved numerically. In contrast with the case without dissipation, the frequencies and growth rates of the different modes depend on the parameters of the unperturbed plasma column. The calculation shows, in qualitative agreement with the experiment, that with increasing magnetic field the highest growth rate passes successively to the next higher mode.

Comparison of self-fields effects in two-stream electromagnetically pumped FEL with ion-channel guiding and axial magnetic field

2011 ◽  
Vol 77 (6) ◽  
pp. 765-776 ◽  
Author(s):  
S. SAVIZ ◽  
H. MEHDIAN ◽  
FARZIN M. AGHAMIR ◽  
M. GHORANNEVIS ◽  
A. A. ASHKARRAN
Keyword(s):  
Magnetic Field ◽  
Ion Channel ◽  
Free Electron ◽  
Free Electron Laser ◽  
Axial Magnetic Field ◽  
Small Region ◽  
Numerical Calculations ◽  
Small Signal Gain ◽  
Small Signal ◽  
Electron Trajectories

AbstractA theory of two-stream free-electron laser in a combined electromagnetic wiggler and an ion-channel guiding is developed. In the analysis, the electron trajectories and the small signal gain are derived by considering the effects of self-fields. Numerical calculations show that there are seven group's trajectories rather than nine groups reported in Mehdian and Saviz (2010 Chin. Phys. B 19(1), 014214). The comparison of the normalized gains and their corresponding normalized frequencies by employing the axial magnetic field and ion-channel guiding, with and without self-fields, in FEL has been studied numerically. The results show that the normalized maximum gain in FEL with axial magnetic is larger than that for using ion-channel guiding except in small region, but the results for their corresponding normalized frequencies are opposite.

Spontaneous generation of magnetic field in an imploding plasma

1984 ◽  
Vol 32 (3) ◽  
pp. 349-357 ◽  
Author(s):  
S. K. H. Auluck
Keyword(s):  
Magnetic Field ◽  
Axial Magnetic Field ◽  
Equations Of Motion ◽  
Field Configuration ◽  
Spontaneous Generation ◽  
Centripetal Acceleration ◽  
Cylindrically Symmetric ◽  
Order Of Magnitude ◽  
Reversed Field ◽  
Metallic Liner

Spontaneous generation of an axial magnetic field is predicted when the usually neglected centripetal acceleration term is properly taken into account in the two-fluid equations of motion for a cylindrically symmetric imploding plasma. An order-of-magnitude calculation is presented to illustrate spontaneous generation of a reversed-field configuration in a plasma imploded by a metallic liner.

scholarly journals The structure of fast sausage waves in current-carrying coronal loops

2014 ◽  
Vol 32 (9) ◽  
pp. 1189-1193 ◽  
Author(s):  
D. B. Bembitov ◽  
B. B. Mikhalyaev ◽  
M. S. Ruderman
Keyword(s):  
Magnetic Field ◽  
Axial Magnetic Field ◽  
Microwave Emission ◽  
Coronal Loops ◽  
Surface Currents ◽  
Azimuthal Magnetic Field ◽  
Principal Mode ◽  
Contraction And Expansion ◽  
The Magnetic Field ◽  
A Current

Abstract. We study fast sausage waves in a model coronal loop that consists of a cylindrical core with axial magnetic field and coaxial annulus with purely azimuthal magnetic field. The magnetic field is discontinuous at the tube and core boundaries, and there are surface currents with the opposite directions on these boundaries. The principal mode of fast sausage waves in which the magnetic pressure perturbation has no nodes in the radial direction can exist for arbitrary wavelength. The results for the fundamental radial mode of sausage waves are applied to the interpretation of observed periodic pulsations of microwave emission in flaring loops with periods of a few tens of seconds. Radial plasma motion has opposite directions at the tube and core boundaries. This leads to the periodic contraction and expansion of the annulus. We assume that the principal mode of fast sausage waves in the current-carrying coronal loops is able to produce a current sheet. However, the nonlinear analysis is needed to confirm this conjecture.

Numerical Simulation of 300mm CZ Silicon Crystal Growth with Axial Magnetic Fields

2011 ◽  
Vol 689 ◽  
pp. 179-183
Author(s):  
Wen Ting Xu ◽  
Hai Ling Tu ◽  
Qing Chang ◽  
Qing Hua Xiao ◽  
Xiao Lin Dai ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Growth Rate ◽  
Crystal Growth ◽  
Magnetic Fields ◽  
Growth Rates ◽  
Axial Magnetic Field ◽  
Silicon Crystal ◽  
Crystal Interfaces ◽  
Hot Zone

We studied the optimization of 300mm CZ silicon crystal growth in 28 inch hot zone with axial magnetic field. The convex of melt-crystal interfaces toward to the crystal are observed in our simulations under different growth velocities (0.3mm/min, 0.5mm/min and 0.65mm/min). The convections in melt were illustrated under different growth rates and intensities of magnetic field. The growth rate of 0.5mm/min and axial magnetic fields intensity of 0.3T were recommended as an appropriate control condition.

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