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AbstractAbstract

[en] To design self-cooled liquid metal blankets for fusion reactors, one must know about the behaviour of MHD flows at high Hartmann numbers. In this work, finite difference codes are used to investigate the influence of Hartmann number M, interaction parameter N, wall conductance ratio c, and changing magnetic field, respectively, on the flow. As liquid-metal MHD flows are characterized by thin boundary layers, resolution of these layers is the limiting issue. Hartmann numbers up to 10

^{3}are reached in the two-dimensional case of fully developed flow, while in three-dimensional flows the limit is 10^{2}. However, the calculations reveal the main features of MHD flows at large M. They are governed by electric currents induced in the fluid. Knowing the paths of these currents makes it possible to predict the flow structure. Results are shown for two-dimensional flows in a square duct at different Hartmann numbers and wall conductivities. The three-dimensional results are also for a square duct. Flow Channel Inserts (FCI), of interest in blanket design, are investigated. They serve to decouple the load carrying wall from the currents in the fluid. The calculations show that the FCI is indeed a suitable measure to reduce the pressure losses in the blanket. (author)Primary Subject

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[en] The free-boundary equilibrium was studied by applying the NEMEC code to the helical advanced stellarator (Helias) configuration. The deformation of an initially circular axisymmetric plasma boundary into the final elliptical boundary of an 1=2 stellarator equilibrium is shown at successive iterations. The ATF, WVII-AS, and Helias free-boundary equilibria are shown for various values fo (β) and also of a superimposed external Bz field. The radial shifts due to (β) and Bz are illustrated. The magnetic field produced by the plasma current is shown for the helias free-boundary equilibrium

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Rau, F. (Max-Planck-Institut fuer Plasmaphysik, Garching (Germany, F.R.)); Leotta, G.G.; Commission of the European Communities, Brussels (Belgium); 411 p; 1987; p. 61-68; Proceedings of the Workshop on Wendelstein VII-X; Schloss Ringberg (Germany, F.R.); 18-20 Mar 1987

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[en] Hydromagnetic natural convection around heavy rotating hot axisymmetric magnets has been studied analytically. The axisymmetric magnets perform uniform rotational motion about the axis of symmetry in huge stationary masses of viscous fluids under the action of gravitational body forces. The influences of all the governing parameters on the flow, heat transfer and energy expenditures to maintain the rotational motions of the solids have been discussed separately. It is seen that the variations in the curvatures of the solid surfaces do not influence directly the balance of the magnetic field distributions due to convection and diffusion, although the velocity field is directly affected by these variations. (author). 3 refs

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AbstractAbstract

[en] The flow of a conducting liquid is studied based on the method of integral magnetohydrodynamic equations

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Transl.: Cover-to-cover translation of Magnitnaya Gidrodinamika (USSR).

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[en] The effect of a finite conductivity on the buildup of a magnetic field in a converging plasma flow is analyzed using incompressible MHD. The results show that in the collapse of a cavity in a conducting fluid a slight magnetic viscosity results in a decay of the field flux in the cavity to zero in accordance with a power law which is unrelated to the property of self-similarity

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Transl.: Cover-to-cover translation of Fizika Plazmy (USSR).

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Translation

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Soviet Journal of Plasma Physics (English Translation); ISSN 0360-0343; ; CODEN SJPPD; v. 14(12); p. 873-876

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[en] The numerical solution of the unsteady flow of electrically conducting Walters liquid B' due to impulsive motion of an infinite non-conducting, non-magnetic horizontal plate in the presence of a transverse magnetic field is studied. The liquid is initially assumed to be at rest. A numerical technique is developed to determine the height to which the disturbance is felt and is found to be a function time (t). The region of disturbance is found to be y=20 at t=1. The velocity is found to increase while K is increased and M is kept constant; the disturbance in vertical direction due to the motion of the plate is found to increase with increase of time and steady state is obtained at t=24. The velocity is found to increase with increase of elastic parameter K. Fluctuations are observed in the velocity in the layers immediately following layer of zero velocity for K=0.04 and K=0.05. The magnetic field is found to be large in the vicinity of the plate, i.e. for y=0 to y=4 and decreases uniformly thereafter. The magnetic field is found to increase as K (or M) increases and M (or K) is kept constant. The magnetic field is found to increase with increase in time. Shear stress τ is found to be large in the vicinity of the plate and decreases thereafter with height. (author). 7 refs

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[en] Arc spots are usually highly unstable and jump statistically over the cathode surface. In a magnetic field parallel to the surface, preferably they move in the retrograde direction; i.e., opposite to the Lorentzian rule. If the field is inclined with respect to the surface, the spots drift away at a certain angle with respect to the proper retrograde direction (Robson drift motion). These well-known phenomena are explained by one stability theory

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[en] Sufficient criteria of linear ideal magnetohydrodynamic stability are derived for a three-dimensional nonlinear force-free magnetic field B occupying an infinite region Ω, which is either a half-space or an ''exterior domain''; all the field lines of B are assumed to be firmly rooted in the boundary ∂Ω of Ω (line-tying condition), but their topological pattern may be otherwise quite arbitrary. Roughly speaking, a field characterized by a length scale Λ is found to be stable if α

_{0}Λ< O(1), where α_{0}is a number measuring the magnitude of the force-free function α=B^{-2}(B·∇xB). The stability criteria established here have some important astrophysical applications (solar corona, magnetosphere of a compact object, etc.), which are briefly discussedPrimary Subject

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[en] A finite element method is given to obtain the solution in terms of velocity and induced magnetic field for the steady MHD (magnetohydrodynamic) flow through a rectangular pipe having arbitrarily conducting walls. Linear and then quadratic approximations have been taken for both velocity and magnetic field for comparison and it is found that with the quadratic approximation it is possible to increase the conductivity and Hartmann number M (M ≤ 100). Computations have been carried out for several values of Hartmann number and wall conductivity. It is also found that, if the wall conductivity increases, the flux decreases. Selected graphs are given showing the behaviour of the velocity field and induced magnetic field. (author)

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Numerical Data

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International Journal for Numerical Methods in Engineering; ISSN 0029-5981; ; CODEN IJNMB; v. 28(2); p. 445-459

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[en] Magnetic fluctuations resulting from the thermally excited magnetohydrodynamic waves are investigated using fluid and kinetic models to describe a stable, uniform, compressible plasma in the range above the drift wave frequency and below the ion cyclotron frequency. It is shown that the fluid model with resistivity yields spectral densities that are roughly Lorentzian and exhibit equipartition with no apparent cutoff in wavenumber space and a Bohm-type diffusion coefficient. Under certain conditions, the ensuing transport may be comparable to classical values. For a phenomenological cutoff imposed on the spectrum, the typical fluctuating-to-equilibrium magnetic field ratio is found to be of the order of 10

^{-10}. Physical mechanisms to obtain decay profiles of the spectra with increasing wavenumber as a result of dispersion and/or different forms of damping are investigated analytically in a cold fluid approximation and numerically, with a kinetic model. The mode dispersion resulting from the finite ion gyro-frequency is identified as the leading effect determining the spectral profile shapes. It is found that the amplitude of fluctuations may be within a factor of the value suggested by the cold plasma model. The results from both models are presented and compared in low- and high-beta regimesPrimary Subject

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