Engineering topics

Khalzov, I V

Publications and source records attributed to Khalzov, I V.

5 records

DOE OSTI2012

Optimized boundary driven flows for dynamos in a sphere

We perform numerical optimization of the axisymmetric flows in a sphere to minimize the critical magnetic Reynolds number Rm{sub cr} required for dynamo onset. The optimization is done for the class of laminar incompressible flows of von Karman type satisfying the steady-state Navier-Stokes equation. Such flows are determined by equatorially antisymmetric profiles of driving azimuthal (toroidal) velocity specified at the spherical boundary. The model is relevant to the Madison plasma dynamo experiment, whose spherical boundary is capable of differential driving of plasma in the azimuthal direction. We show that the dynamo onset in this system depends strongly on details of the driving velocity profile and the fluid Reynolds number Re. It is found that the overall lowest Rm{sub cr} Almost-Equal-To 200 is achieved at Re Almost-Equal-To 240 for the flow, which is hydrodynamically marginally stable. We also show that the optimized flows can sustain dynamos only in the range Rm{sub cr}<Rm<Rm{sub cr2}, where Rm{sub cr2} is the second critical magnetic Reynolds number, above which the dynamo is quenched. Samples of the optimized flows and the corresponding dynamo fields are presented.

42 ENGINEERING↗

DOE OSTI2012

Resistive and ferritic-wall plasma dynamos in a sphere

We numerically study the effects of varying electric conductivity and magnetic permeability of the bounding wall on a kinematic dynamo in a sphere for parameters relevant to Madison plasma dynamo experiment. The dynamo is excited by a laminar, axisymmetric flow of von Karman type. The flow is obtained as a solution to the Navier-Stokes equation for an isothermal fluid with a velocity profile specified at the sphere's boundary. The properties of the wall are taken into account as thin-wall boundary conditions imposed on the magnetic field. It is found that an increase in the permeability of the wall reduces the critical magnetic Reynolds number Rm{sub cr}. An increase in the conductivity of the wall leaves Rm{sub cr} unaffected but reduces the dynamo growth rate.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Minimum energy states of the cylindrical plasma pinch in single-fluid and Hall magnetohydrodynamics

Relaxed states of a plasma column are found analytically in single-fluid and Hall magnetohydrodynamics (MHD). We perform complete minimization of the energy with constraints imposed by invariants inherent in the corresponding models. It is shown that the relaxed state in Hall MHD is a force-free magnetic field with uniform axial flow and/or rigid azimuthal rotation. In contrast, the relaxed states in single-fluid MHD are more complex due to the coupling between velocity and magnetic field. Cylindrically and helically symmetric relaxed states are considered for both models. Helical states may be time dependent and analogous to helical waves, propagating on a cylindrically symmetric background. Application of our results to reversed-field pinches (RFP) is discussed. The radial profile of the parallel momentum predicted by the single-fluid MHD relaxation theory is shown to be in reasonable agreement with experimental observation from the Madison symmetric torus RFP experiment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

Numerical simulation of laminar plasma dynamos in a cylindrical von Karman flow

The results of a numerical study of the magnetic dynamo effect in cylindrical von Karman plasma flow are presented with parameters relevant to the Madison Plasma Couette Experiment. This experiment is designed to investigate a broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl number Pm can be of order unity (i.e., the fluid Reynolds number Re is comparable to the magnetic Reynolds number Rm). This is in contrast to liquid metal experiments, where Pm is small (so, Re>>Rm) and the flows are always turbulent. We explore dynamo action through simulations using the extended magnetohydrodynamic NIMROD code for an isothermal and compressible plasma model. We also study two-fluid effects in simulations by including the Hall term in Ohm's law. We find that the counter-rotating von Karman flow results in sustained dynamo action and the self-generation of magnetic field when the magnetic Reynolds number exceeds a critical value. For the plasma parameters of the experiment, this field saturates at an amplitude corresponding to a new stable equilibrium (a laminar dynamo). We show that compressibility in the plasma results in an increase of the critical magnetic Reynolds number, while inclusion of the Hall term in Ohm's law changes the amplitude of the saturated dynamo field but not the critical value for the onset of dynamo action.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2010

What physics does affect the MRI threshold

Several physical effects, which can considerably decrease the magnetorotational instability (MRI) threshold are discussed. First, we show that MRI features are changed significantly in non-uniform magnetic field. Second, the buoyancy effect is shown to can be destabilizing for azimuthal flow of a resistive plasma. Third, we demonstrate that the rotating fluid may be unstable with respect to non-axisymmetric modes at much lower rotation velocities than with respect to usual symmetric modes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗