Showing papers by "Frank Stefani published in 2003"
TL;DR: In this paper, the history of the underlying theory and comment on previous attempts to realize homogeneous dynamos inthe laboratory are discussed. And a preliminary interpretation of the measured data is also presented.
Abstract: Cosmic magnetic fields, including the magnetic field of the Earth,are produced by the homogeneous dynamo effect in moving electricallyconducting fluids. We sketch the history of the underlying theoryand comment on previous attempts to realize homogeneous dynamos inthe laboratory. For the main part, we report on two series ofexperiments carried out at the Riga dynamo facility. In November1999 a slowly growing magnetic field eigenmode was observed forthe first time in a liquid metal experiment. In July 2000, themagnetic field saturation regime was studied and a number ofinteresting back-reaction effects were observed. A preliminaryinterpretation of the measured data is also presented.
54 citations
TL;DR: This work finds oscillatory mean-field dynamos of the alpha(2) type with spherically symmetric and isotropic turbulence parameter alpha by means of an evolutionary strategy, and illustrates the spectral properties of the corresponding dynamo operators.
Abstract: Until recently, the existence of oscillatory mean-field dynamos of the ${\ensuremath{\alpha}}^{2}$ type with spherically symmetric and isotropic turbulence parameter $\ensuremath{\alpha}$ was an open question. We find such dynamos by means of an evolutionary strategy, and we illustrate the spectral properties of the corresponding dynamo operators.
47 citations
TL;DR: In this article, the isospectrality problem of the spherical hydromagnetic α2-dynamo operator matrix is studied and an intrinsic structural inconsistency is obtained in the set of associated Riccati equations.
Abstract: The isospectrality problem is studied for the operator of the spherical hydromagnetic α2-dynamo. It is shown that this operator is formally pseudo-Hermitian (J-symmetric) and lives in a Krein space. Based on the J-symmetry, an operator intertwining Ansatz with first-order differential intertwining operators is tested for its compatibility with the structure of the α2-dynamo operator matrix. An intrinsic structural inconsistency is obtained in the set of associated matrix Riccati equations. This inconsistency is interpreted as a no-go theorem which forbids the construction of isospectral α2-dynamo operator classes with the help of first-order differential intertwining operators.
32 citations
TL;DR: In this article, the authors consider inverse problems related to the velocity reconstruction in electrically conducting fluids from externally measured magnetic fields, and present results of an experiment in which the three-dimensional velocity field of a propellor driven flow in a liquid metal is reconstructed by a contactless inductive measuring technique.
Abstract: We consider inverse problems related to the velocity reconstruction in electrically conducting fluids from externally measured magnetic fields. The underlying theory is presented in the framework of the integral equation approach to homogeneous dynamos in finite domains, which can be cast into a linear inverse problem in case that the magnetic Reynolds number is not too large. Some mathematical problems of the inversion, including the uniqueness problem in the sphere and a paradigmatic isospectrality problem for mean-field dynamos, are touched upon. For practical purposes, the inversion is carried out with the help of Tikhonov regularization using a quadratic functional of the velocity field as penalty function. For the first time, we present results of an experiment in which the three-dimensional velocity field of a propellor driven flow in a liquid metal is reconstructed by a contactless inductive measuring technique.
1 citations