Effect of collisionality on kinetic stability of the resistive wall mode

The impact of collisionless, energy-independent, and energy-dependent collisionality models on the kinetic stability of the resistive wall mode is examined for high pressure plasmas in the National Spherical Torus Experiment. Future devices will have decreased collisionality, which previous stability models predict to be universally destabilizing. In contrast, in kinetic theory reduced ion-ion collisions are shown to lead to a significant stability increase when the plasma rotation frequency is in a stabilizing resonance with the ion precession drift frequency. When the plasma is in a reduced stability state with rotation in between resonances, collisionality will have little effect on stability.     

Classical perfect diamagnetism: expulsion of current from the plasma interior

The vanishing of generalized helicity is shown to be the necessary and sufficient condition for a perfect conductor to display perfect diamagnetism, considered to be the defining attribute of a conventional superconductor. Although conventional superconductivity is brought about by quantum correlations in classical systems, prepared in the state of zero initial helicity (helicity is a constant of the motion for a perfect conductor), it can mimic the superconductor's behavior.     

On the Landau diamagnetism

The grand-canonical partition function of an assembly of free spinless electrons in a magnetic field enclosed in a box (Dirichlet boundary conditions) is shown to be an entire function of the fugacityz and the magnetic fieldH, as a consequence of the trace-norm convergence of the perturbation series for the statistical semigroup. This allows to derive analyticity properties of the pressure as a function ofz andH, and to express the coefficients of its power series expansion aroundz=H=0 by means of the unperturbed semigroup. Hence, the magnetic susceptibility at zero field and fixed density is expressed in terms of Green functions of the heat equation. Its asymptotic expansion for Λ→∞ (Fisher) along parallelepipedic domains is obtained up to 0 (S(Λ)/V(Λ)). The volume term of this expansion is the Landau diamagnetism.     

Effect of electromagnetic boundary condition on dynamo actions

In this paper,based on the mean field dynamo theory,the influence of the electromagnetic boundary condition on the dynamo actions driven by the small scale turbulent flows in a cylindrical vessel is investigated by the integral equation approach.The numerical results show that the increase of the electrical conductivity or magnetic permeability of the walls of the cylindrical vessel can reduce the critical magnetic Reynolds number.Furthermore,the critical magnetic Reynolds number is more sensitive to the varying electrical conductivity of the end wall or magnetic permeability of the side wall.For the anisotropic dynamo which is the mean field model of the Karlsruhe experiment,when the relative electrical conductivity of the side wall or the relative magnetic permeability of the end wall is less than some critical value,the m=1(m is the azimuthal wave number)magnetic mode is the dominant mode,otherwise the m=0 mode predominates the excited magnetic field.Therefore,by changing the material of the walls of the cylindrical vessel,one can select the magnetic mode excited by the anisotropic dynamo.     

On diamagnetism and non-dissipative transport

The states of free electrons in a magnetic field confined to a box of finite volume are determined and used to calculate the average magnetic moment and the non-dissipative electric and heat current in an unambiguous way. It is shown that for infinite volume the average magnetic moment coincides with the magnetization calculated by Landau. Similarly, for infinite volume, the non-dissipative transport coefficients coincide with those calculated by Zyryanov and Silin who use Landau's method and subtract the purely diamagnetic parts from the total currents. We think that our considerations give an answer to the often discussed question, why the Landau calculation of the magnetization and similar calculations of the non-dissipative transport coefficients are correct for a large system.     

Measurement of the Hall dynamo effect during magnetic reconnection in a high-temperature plasma

The fluctuation-induced Hall electromotive force, [deltaJ x deltaB]/nee, is experimentally measured in the high-temperature interior of a reversed-field pinch plasma by a fast Faraday rotation diagnostic. It is found that the Hall dynamo effect is significant, redistributing (flattening) the equilibrium core current near the resonant surface during a reconnection event. These results imply that effects beyond single-fluid MHD are important for the dynamo and magnetic reconnection.     

Design of diamagnetic coil with non-encircling compensation coil system for measuring the plasma diamagnetism in toroidal devices

The paper describes a new scheme for suppressing the unwanted and dominant coupling of the diamagnetic coil with the toroidal field coils of a tokamak device.     

Influence of turbulence on the dynamo threshold

We use direct and stochastic numerical simulations of the magnetohydrodynamic equations to explore the influence of turbulence on the dynamo threshold. In the spirit of the Kraichnan-Kazantsev model, we model the turbulence by a noise, with given amplitude, injection scale, and correlation time. The addition of a stochastic noise to the mean velocity significantly alters the dynamo threshold and increases it for any noise at large scale. For small-scale noise, the result depends on its correlation time and on the magnetic Prandtl number.     

Nonlinear diamagnetism due to the fluctuation superconductivity

Nonlinear susceptibility due to the fluctuation superconductivity is calculated microscopically in the Ginzburg-Landau-Garkov approximation. The characteristic field of the nonlinearity is given by H_c2.     

Hydrogen absorption and field-dependent diamagnetism of SmNiAl

Hydrogen absorption properties of SmNiAl were systematically investigated between room temperature and 673 K over the pressure range from 0 to 10 MPa. It absorbs hydrogen without clear plateaus, forms hydride SmNiAlH_x (x=0.75–2.04) without structural change below 623 K and decomposes into SmH₂ and NiAl at higher temperatures. Then, the magnetic curves, the field-cooled (FC) and the zero-field-cooled (ZFC) susceptibilities of SmNiAl and its hydride were investigated. SmNiAl behaves as paramagnetic above 65 K, but has three antiferromagnetic transitions at lower temperatures. Hydrogenation enhances its magnetism, but weakens the interaction between magnetic moments. In the FC process, hydrogenation especially induces an anomalous diamagnetism. Mechanisms for the hydrogen absorption, structural change and magnetism were discussed.     

Corrections to the Landau diamagnetism of liquid metals

Perturbation corrections to the free electron value of the Landau susceptibility have been obtained in terms of an electron-ion pseudopotential and the structure factor of the liquid metal.     

物质抗磁性的经典统计解释

介绍一种解释物质抗磁性的经典统计方法.     

Landau diamagnetism and magnetization of interacting disordered conductors

We show how the orbital magnetization of an interacting diffusive electron gas can be simply related to the magnetization of the noninteracting system having the same geometry. This result is applied to the persistent current of a mesoscopic ring and to the relation between Landau diamagnetism and the interaction correction to the magnetization of diffusive systems. The field dependence of this interaction contribution can be deduced directly from the de Haas-van Alphen oscillations of the free electron gas. Known results for the free orbital magnetism of finite systems can be used to derive the interaction contribution in the diffusive regime in various geometries.     

Francis Bitter and “Landau diamagnetism”

A forgotten paper by Francis Bitter on the diamagnetism of a quantum electron gas, published in 1930, is discussed. By an approximate method, later considered unsatisfactory, Bitter obtained a result qualitatively similar to the standard formula first established by Landau in the same year. Editor's note: This paper is intended as an historical note and is published in keeping with our policy of publishing such documentary material from time to time. 3 See, for example, the obituary in theNew York Times, July 27, 1967.