Solidification microstructures and solid-state parallels: Recent developments, future directions

A nonlinear gyrokinetic formalism for low‐frequency (less than the cyclotron frequency) microscopic electromagnetic perturbations in general magnetic field configurations is developed. The nonlinear equations thus derived are valid in the strong‐turbulence regime and contain effects due to finite Larmor radius, plasma inhomogeneities, and magnetic field geometries. The specific case of axisymmetric tokamaks is then considered and a model nonlinear equation is derived for electrostatic drift waves. Also, applying the formalism to the shear Alfven wave heating scheme, it is found that nonlinear ion Landau damping of kinetic shear‐Alfven waves is modified, both qualitatively and quantitatively, by the diamagnetic drift effects. In particular, wave energy is found to cascade in wavenumber instead of frequency.

Nonlinear gyrokinetic equations for low-frequency electromagnetic waves in general plasma equilibria

Solidification microstructures: recent developments, future directions

Proposed fusion and advanced (Generation IV) fission energy systems require high-performance materials capable of satisfactory operation up to neutron damage levels approaching 200 atomic displacements per atom with large amounts of transmutant hydrogen and helium isotopes. After a brief overview of fusion reactor concepts and radiation effects phenomena in structural and functional (nonstructural) materials, three fundamental options for designing radiation resistance are outlined: Utilize matrix phases with inherent radiation tolerance, select materials in which vacancies are immobile at the design operating temperatures, or engineer materials with high sink densities for point defect recombination. Environmental and safety considerations impose several additional restrictions on potential materials systems, but reduced-activation ferritic/martensitic steels (including thermomechanically treated and oxide dispersion–strengthened options) and silicon carbide ceramic composites emerge as robust structural...

Designing Radiation Resistance in Materials for Fusion Energy

Two-dimensional turbulence: a physicist approach

A description of MHD turbulence at low magnetic Reynolds number and large interaction parameter is proposed, in which attention is focussed on the role of insulating walls perpendicular to a uniform applied magnetic field. The flow is divided in two regions: the thin Hartmann layers near the walls, and the bulk of the flow. In the latter region, a kind of electromagnetic diffusion along the magnetic field lines (a degenerate form of Alfv6n waves) is displayed, which elongates the turbulent eddies in the field direction, but is not sufficient to generate a two-dimensional dynamics. However the normal derivative of velocity must be zero (to leading order) at the boundaries of the bulk region (as at a free surface), so that when the length scale 1, perpendicular to the magnetic field is large enough, the corresponding eddies are necessarily two-dimensional. Furthermore, if I, is not larger than a second limit, the Hartmann braking effect is negligible and the dynamics of these eddies is described by the ordinary Navier-Stokes equations without electromagnetic forces. MHD then appears to offer a means of achieving experiments on two-dimensional turbulence, and of deducing velocity and vorticity from measurements of electric field.

Why, how, and when, MHD turbulence becomes two-dimensional

Modification of interdendritic convection in directional solidification by a uniform magnetic field

Magnetohydrodynamics : Historical evolution and trends

This paper presents a model for quasi-two-dimensional MHD flows between two planes with small magnetic Reynolds number and constant transverse magnetic field orthogonal to the planes. A method is presented that allows three-dimensional effects to be taken into account in a two-dimensional equation of motion thanks to a model for the transverse velocity profile. This model is obtained by using a double perturbation asymptotic development both in the core flow and in the Hartmann layers arising along the planes. A new model is thus constructed that describes inertial effects in these two regions. Two separate classes of phenomena are found: one related to inertial effects in the Hartmann layer gives a model for recirculating flows and the other introduces the possibility of having a transverse dependence of the velocity profile in the core flow. The ‘recirculating’ velocity profile is then introduced in the transversally averaged equation of motion in order to provide an effective two-dimensional equation of motion. Analytical solutions of this model are obtained for two experimental configurations: isolated vortices generated by a point electrode and axisymmetric parallel layers occurring in the MATUR (MAgneticTURbulence) experiment. The theory is found to give a satisfactory agreement with the experiment so that it can be concluded that recirculating flows are actually responsible for both vortex core spreading and excessive dissipative behaviour of the axisymmetric sidewall layers.

An effective two-dimensional model for MHD flows with transverse magnetic field

Session A : Large Interaction Parameter.- Liquid metal in a strong magnetic field (General Lecture).- Numerical solutions of three-dimensional MHD flows in strong non-uniform transverse magnetic fields.- MHD-flows at high Rm, N and Ha.- MHD pressure drop of liquid metal flow in circular and rectangular ducts under transverse magnetic field.- Linear approximation application limits in MHD-flow theory for strong magnetic fields. Experimental results.- Session B : Fusion Related Flows.- Application of the core flow approach to MHD fluid flow in geometric elements of a fusion reactor blanket.- Experimental and theoretical work on MHD at the kernforschungszentrum Karlsruhe. The MEKKA-program.- Liquid metal turbulent flow phenomena and their implications on fusion reactor blanket design.- Experimental investigation of 3-D MHD flows at high Hartmann number and interaction parameter.- Magnetohydrodynamics in nuclear energetics (General lecture).- Poster Session 1 : DC Fields.- Liquid metal flows with polydispersed solid and gaseous inclusions.- Dispersion of small particles in MHD flows.- Two-phase flows studies in mercury-air liquid metal MHD generators.- Liquid metal MHD generators in two-phase flow systems.- Modelling of magnetohydrodynamic two-phase flow in pipe.- Melt magnetohydrodynamics of single crystal growth.- The effect of electromagnetic field on semiconductor single crystal growth and characteristics.- Gas bubbles motion during vacuum treatment of liquid aluminium in MDV-type devices.- MHD turbulence decay behind spatial grids.- The effect of a uniform magnetic field on stability, transition and turbulence as a control means for liquid metal flow mixing.- Session C : Current Carrying Melts.- Electrically induced vortical flows (General lecture).- Liquid metal flow near magnetic neutral points.- Modelling of electrically induced flows for studying current carrying melts of electrometallurgical devices.- Session D : Aluminium Reduction Cells.- Amplitude evolution of interfacial waves in aluminium reduction cells.- Physical and mathematical modeling of MHD-processes in aluminium reduction cells.- On the analysis by perturbation methods of the anodic current fluctuations in an electrolytic cell for aluminium production.- Session E : AC Stirring.- Fluid flows induced by alternating magnetic (General lecture).- Fluid metal flow study in an induction furnace based on numerical simulation.- A high frequency induction furnace for oxide melting.- Directional melt-flow in channel induction furnaces.- Characteristic properties of MHD flow in magnetodynamic pumps.- Session F : Electromagnetic Shaping.- Deflection of a stream of liquid metal by means of an alternating magnetic field.- The shape of liquid metal jets under a uniform transverse magnetic field.- Electromagnetic control of liquid metal free surfaces.- Deformation of an electrically conducting drop in a magnetic field.- Controlled decomposition of liquid metal jets and films in technological and power devices.- Poster Session 2 : AC Fields.- More accurate skin-depth approximation.- Overall and local thickness measurement of layers with differing electrical properties.- Determination of MHD machine parameters using the 1D model of a non-uniform flow.- Experimental and theoretical studies on the stability of induction pumps at large Rm numbers.- 3500 m3/h MHD pump for fast breeder reactor.- Self-excitation of liquid metal MHD generators.- Comprehensive study on the MHD phenomena in the metal pool with the single-phase induction coil.- Grain refinement in continously cast ingots of light metals by electromagnetic casting.- Liquid metal flow control using AC fields.- Session G : Measurements.- Diagnostics of liquid metal flows using fibre-optic velocity sensor.- On local measurements of the up and downstream magnetic wake of a cylinder at low magnetic Reynolds number.- Metallurgical aspects of electromagnetic processing of materials (General lecture).- Session H : Dynamo Theory.- Liquid metal MHD and the geodynamo (General lecture).- The helical MHD dynamo.- The Ponomarenko dynamo.- MHD phenomena in fast neutron reactors with a liquid metal heat carrier.- Session I : Turbulence.- The effect of initial and boundary conditions upon the formation and development of MHD turbulence structure.- Two-dimensional MHD turbulence.- MHD instabilities and turbulence in liquid metal shear flows.- Session J : Stability with Uniform Field.- Dispersion and chaos in linear arrays of vortices.- Stability of magnetohydrodynamic flow over a stretching sheet.- Stability of closed azimuthal jet of liquid metal.

Rene Moreau

Papers

Why, how, and when, MHD turbulence becomes two-dimensional

Modification of interdendritic convection in directional solidification by a uniform magnetic field

Magnetohydrodynamics : Historical evolution and trends

An effective two-dimensional model for MHD flows with transverse magnetic field

Liquid metal magnetohydrodynamics