AXISYMMETRIC RESISTIVE INSTABILITIES IN THE HARD-CORE PINCH

1966 ◽  
Vol 44 (5) ◽  
pp. 1037-1046 ◽  
Author(s):  
R. J. Hosking ◽  
J. H. Blackwell
Keyword(s):  
Magnetic Field ◽  
Growth Rates ◽  
Hydrogen Plasma ◽  
Practical Importance ◽  
Hard Core ◽  
Finite Conductivity ◽  
Core System ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Plasma Diffusion

The hard-core pinch configuration with azimuthal equilibrium magnetic field only is considered. Provided finite conductivity is included, unstable axisymmetric modes are found. These instabilities are apparently due to nonlocalized plasma diffusion across the magnetic flux lines. On the laboratory scale, the growth rates do not appear to be significant, when the material of the conducting shell is mercury. For a hydrogen plasma shell, however, it appears that the growth rates may be of practical importance. It is found that the ratio of the current in the shell to the hard-core current has a significant effect on the "spectrum" of instabilities. This effect in part accounts for the observed relative stability of the hard-core system when there is no axial equilibrium magnetic field.

scholarly journals Effect of Aerosil and Oleic Acid on Sedimentation of Magnetorheological Fluid

2019 ◽  
Vol 8 (12S2) ◽  
pp. 79-83
Keyword(s):  
Magnetic Field ◽  
Oleic Acid ◽  
Magnetic Force ◽  
Particle Concentration ◽  
Nano Particles ◽  
Carrier Fluid ◽  
Flux Lines ◽  
Smart Fluids ◽  
Magnetic Flux Lines ◽  
Ferro Magnetic

Magnetorheological Fluids (MRFs) are considered as smart fluids because they control viscosity using external magnetic field. It contains ferro-magnetic powder which are aligned in magnetic flux lines. The magnetic force between particles are controlled by magnetic field intensity. This controllable viscosity makes them acceptable in many mechanical applications, but due to difference in density between suspended particles and carrier fluid sedimentation is bound to occur. This thus creates the need of some additives. In our study, silica Nano particles (commercially known as Aerosil 200) is used as stabilizer and Oleic Acid is used as surfactant and their effect on sedimentation is studied in this article. Some other synthesis parameters like particle concentration, stirring duration and material loading also cause some change in sedimentation rate.

Magnetic Circuit Simulation for Magnetorheological (MR) Fluids Testing Rig in Squeeze Mode

2010 ◽  
Vol 123-125 ◽  
pp. 991-994 ◽  
Author(s):  
Izwan Ismail ◽  
Saiful Amri Mazlan ◽  
Abdul Ghani Olabi
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Field Distribution ◽  
Circuit Simulation ◽  
Magnetic Field Distribution ◽  
Mr Fluid ◽  
Flux Lines ◽  
Mr Fluids ◽  
Magnetic Flux Lines ◽  
The Magnetic Field

In this study, a testing rig in squeeze was designed and developed with the ability to conduct various tests especially for quasi-static squeezing at different values of magnetic field strength. Finite Element Method Magnetics (FEMM) was utilized to simulate the magnetic field distribution and magnetic flux lines generation from electromagnetic coil to the testing rig. Tests were conducted with two types of MR fluid. MRF-132DG was used to obtain the behaviour of MR fluid, while synthesized epoxy-based MR fluid was used for investigating the magnetic field distribution with regards to particle chains arrangement. Simulation results of the rig design showed that the magnetic flux density was well distributed across the tested materials. Magnetic flux lines were aligned with force direction to perform squeeze tests. Preliminary experimental results showed that stress-strain pattern of MR fluids were in agreement with previous results. The epoxy-based MR samples produced excellent metallographic samples for carbonyl iron particles distributions and particle chain structures investigation.

Finite Element Modeling and Analysis of Magnetorheological Dampers

2011 ◽  
Author(s):  
David Case ◽  
Behzad Taheri ◽  
Edmond Richer
Keyword(s):  
Magnetic Field ◽  
Finite Element ◽  
Magnetic Flux ◽  
Weight Ratio ◽  
Magnetorheological Damper ◽  
Plastic Behavior ◽  
Magnetorheological Dampers ◽  
Flux Lines ◽  
Finite Element Software ◽  
Magnetic Flux Lines

A magnetorheological fluid consists of a suspension of microscopic magnetizable particles in a non-magnetic carrier medium. In the absence of a magnetic field, the fluid behaves in a roughly Newtonian manner. When a magnetic field is produced in the same space, the microscopic particles suspended in the fluid become oriented and form chains along the magnetic flux lines, changing the fluid’s rheology. The orientation of these particle chains is crucial to producing the Bingham plastic behavior necessary for high strength-to-weight ratio magnetorheological dampers and actuators. This project uses COMSOL Multiphysics finite element software to examine the magnetic flux lines, field intensity, and non-Newtonian fluid flow within a magnetorheological damper. Several established and novel damper configurations are examined and modified to improve performance while minimizing power draw of the electromagnet.

scholarly journals Parallel Viscous Modification of the Resistive "Tearing" Instability in a Cartesian Model of the Hard-Core Pinch

1971 ◽  
Vol 24 (4) ◽  
pp. 929 ◽  
Author(s):  
GM Marinoff
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Growth Rates ◽  
Hard Core ◽  
Thermonuclear Reactor ◽  
Tearing Instability

There is continuing interest in the possibility that a diffuse pinch may be used to achieve plasma containment in the laboratory, and ultimately lead to a successful thermonuclear reactor. Such a system is likely to be stabilized against hydromagnetic modes by strong magnetic field shear, but the question of stability against resistive modes remains. In this note, a Cartesian model is adopted, and the influence of "parallel" viscosity (Stringer 1970) on the resistive "tearing" instability in the hard-core pinch is examined. Previously, purely resistive calculations of growth rates in this configuration have been reported by Hosking (1967) and Lister and Hosking (1970).

Hydrothermal wave instability of thermocapillary-driven convection in a coplanar magnetic field

1997 ◽  
Vol 347 ◽  
pp. 141-169 ◽  
Author(s):  
JĀNIS PRIEDE ◽  
GUNTER GERBETH
Keyword(s):  
Magnetic Field ◽  
Marangoni Number ◽  
Travelling Waves ◽  
Return Flow ◽  
Electrically Conducting ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Critical Marangoni Number ◽  
The Stability ◽  
The Magnetic Field

We study the linear stability of surface-tension-driven unidirectional shear flow in an unbounded electrically conducting liquid layer heated from the side and subjected to a uniform magnetic field in the plane of the layer. The threshold of convective instability with respect to oblique travelling waves is calculated depending on the strength and orientation of the magnetic field. For longitudinal waves the critical Marangoni number and the corresponding wavelength are found to increase directly with the induction of a sufficiently strong magnetic field. In general, a coplanar magnetic field causes stabilization of all disturbances except those aligned with the field, which are not influenced at all. With increase of the magnetic field this effect results in the alignment of the most unstable disturbance along the magnetic flux lines. The maximal stabilization is ensured by the magnetic field being imposed spanwise to the basic flow. The corresponding critical Marangoni number is found to be almost insensitive to the thermal properties of the bottom. The strength of the magnetic field necessary to attain the maximal stabilization for a thermally well-conducting bottom is considerably lower than that for an insulating bottom. The basic return flow is found to be linearly stable with respect to purely hydrodynamic disturbances. This effect determines the stability of the basic state with respect to transverse hydrothermal waves at Prandtl number Pr<Prc=0.018. For such a small Pr no alignment of the critical perturbation with a spanwise magnetic field is possible, and the critical Marangoni number can be increased almost directly with the strength of the magnetic field without limit.

Intensification of magnetic field by concentrate-and-stretch of magnetic flux lines

1998 ◽  
Vol 10 (2) ◽  
pp. 457-468 ◽  
Author(s):  
Hideaki Kitauchi ◽  
Shigeo Kida
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Lines ◽  
Magnetic Flux Lines

Application of Alternating Rotating Magnetic Field to Electromagnetic Barrel Finishing

2012 ◽  
Vol 723 ◽  
pp. 466-470
Author(s):  
Z.Q. Liu ◽  
Y. Chen ◽  
J. Teng
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Rotating Magnetic Field ◽  
Magnetic Flux Density ◽  
Distribution Law ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Working Principle ◽  
Barrel Finishing ◽  
The Magnetic Field

The working principle of the electromagnetic barrel finishing machine as well as the generating mechanism and effect of the alternating rotating magnetic field are analyzed, based on the electromagnetic theory to establish a mathematical model of the rotating magnetic field, by the ANSYS finite-element method, resolved the effect of the magnetic flux density and magnetic field strength impacted on the grinding pressure, the electromagnetic finishing machine internal magnetic flux lines distribution law is analyzed under the influence of the alternating rotating magnetic field, finally the reasonableness of the magnetic field distribution is verified by experiments and the electromagnetic finishing machine has been optimized.

THE MAGNETIC TORQUE EXERTED ON A FINITE CYLINDRICAL CONDUCTOR SLAB BY A "ROTATING" MAGNETIC FIELD

1963 ◽  
Vol 41 (2) ◽  
pp. 384-390
Author(s):  
L. L. Lengyel
Keyword(s):  
Magnetic Field ◽  
Perturbation Technique ◽  
Three Dimensional ◽  
Field Vector ◽  
Rotating Magnetic Field ◽  
End Effects ◽  
Cylindrical Conductor ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Magnetic Induction Field

A cylindrical conductor of finite length revolves slowly in a magnetic field given by a constant, rotating field vector. The magnetic flux lines are normal to the axis of the cylinder. The induced axial currents are deflected at the ends of the conductor slab, and a three-dimensional, antisymmetric current distribution results. A perturbation technique is applied to the nondimensional equations defining the electromagnetic field and force distributions. The zeroth-order solution corresponding to an unperturbed magnetic induction field is carried out in detail. The end effects are found to be substantial if the length to diameter ratio is less than 5.

Xenon ion irradiation of superconducting YBa2Cu3O7 thin films

1990 ◽  
Vol 48 (4) ◽  
pp. 92-93
Author(s):  
H. Watanabe ◽  
B. Kabius ◽  
B. Roas ◽  
K. Urban
Keyword(s):  
Defect Formation ◽  
Ion Irradiation ◽  
High Resolution Electron Microscopy ◽  
Structural Disorder ◽  
Flux Lines ◽  
Pinning Effect ◽  
Magnetic Flux Lines ◽  
Resolution Electron ◽  
Radiation Induced ◽  
Induced Defects

Recently it was reported that the critical current density(Jc) of YBa2Cu2O7, in the presence of magnetic field, is enhanced by ion irradiation. The enhancement is thought to be due to the pinning of the magnetic flux lines by radiation-induced defects or by structural disorder. The aim of the present study was to understand the fundamental mechanisms of the defect formation in association with the pinning effect in YBa2Cu3O7 by means of high-resolution electron microscopy(HRTEM).The YBa2Cu3O7 specimens were prepared by laser ablation in an insitu process. During deposition, a substrate temperature and oxygen atmosphere were kept at about 1073 K and 0.4 mbar, respectively. In this way high quality epitaxially films can be obtained with the caxis parallel to the <100 > SrTiO3 substrate normal. The specimens were irradiated at a temperature of 77 K with 173 MeV Xe ions up to a dose of 3.0 × 1016 m−2.

Real-time observation of vortex lattices in a superconductor

1993 ◽  
Vol 51 ◽  
pp. 1050-1051
Author(s):  
K. Harada ◽  
T. Matsuda ◽  
J.E. Bonevich ◽  
M. Igarashi ◽  
S. Kondo ◽  
...  
Keyword(s):  
Real Time ◽  
Flux Line ◽  
Electron Holography ◽  
Lorentz Microscopy ◽  
Vortex Lattices ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Time Observation ◽  
Thin Superconductor ◽  
Real Time Observation

Previous observations of magnetic flux-lines (vortex lattices) in superconductors, such as the field distribution of a flux-line, and flux-line dynamics activated by heat and current, have employed the high spatial resolution and magnetic sensitivity of electron holography. And recently, the 2-D static distribution of vortices was also observed by this technique. However, real-time observations of the vortex lattice, in spite of scientific and technological interest, have not been possible due to experimental difficulties. Here, we report the real-time observation of vortex lattices in a thin superconductor, by means of Lorentz microscopy using a 300 kV field emission electron microscope. This technique allows us to observe the dynamic motion of individual vortices and record the events on a VTR system.The experimental arrangement is shown in Fig. 1. A Nb thin film for transmission observation was prepared by chemical etching. The grain size of the film was increased by annealing, and single crystals were observed with a thickness of 50∼90 nm.

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