Olgerts Lielausis

Detection of a flow induced magnetic field eigenmode in the riga dynamo facility

In a closed volume of molten sodium an intense single-vortex-like helical flow has been produced by an outside powered propeller. At a flow rate of 0.67 m(3)/s a slowly growing magnetic field eigenmode was detected. For a slightly lower flow, additional measurements showed a slow decay of this mode. The measured results correspond satisfactorily with numerical predictions for the growth rates and frequencies.

Magnetic Field Saturation in the Riga Dynamo Experiment

After the dynamo experiment in November 1999 [A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000)] had shown magnetic field self-excitation in a spiraling liquid metal flow, in a second series of experiments emphasis was placed on the magnetic field saturation regime as the next principal step in the dynamo process. The dependence of the strength of the magnetic field on the rotation rate is studied. Various features of the saturated magnetic field are outlined and possible saturation mechanisms are discussed.

Control of Flow Separation Using Electromagnetic Forces

If a fluid is electrically conductive, its flow may be controlled using electromagnetic forces. Meanwhile, this technique is a recognized tool even on an industrial scale for handling highly conductive materials like liquid metals. However, also fluids of low electrical conductivity as considered in the present study, like sea-water and other electrolytes, permit electromagnetic flow control. Experimental results on the prevention of flow separation by means of a streamwise, wall parallel Lorentz force acting on the suction side of inclined flat plates and hydrofoils will be presented.

Riga dynamo experiment and its theoretical background

It is widely believed that almost all magnetic fields in a natural environment are the result of the dynamo process—the field generation in moving nearly homogeneous electro-conducting fluids. This dynamo process occurs in the depths of celestial bodies such as the Earth, most of the planets, the Sun, other stars, and even galaxies. The Riga dynamo experiment is not intended as a model of any particular celestial body. It aims at demonstrating the basic dynamo mechanism—that the intense motion in a large volume of a good electro-conducting liquid creates a magnetic field. In the present paper, the set-up and the main results of this experiment are presented, with some focus on the theoretical interpretation of the data.

The Riga Dynamo Experiment

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.

History and results of the Riga dynamo experiments

Abstract On 11 November 1999, a self-exciting magnetic eigenfield was detected for the first time in the Riga liquid sodium dynamo experiment. We report on the long history leading to this event, and on the subsequent experimental campaigns which provided a wealth of data on the kinematic and the saturated regime of this dynamo. The present state of the theoretical understanding of both regimes is delineated, and some comparisons with other laboratory dynamo experiments are made. To cite this article: A. Gailitis et al., C. R. Physique 9 (2008).

Laboratory astrophysics as exemplified by the Riga dynamo experiment

It has been proposed to investigate the magnetorotational instability at a large scale liquid sodium facility. This sort of laboratory astrophysics is encouraged by the recent successful dynamo experiments. We report on our experiences with the Riga dynamo experiment where magnetic field self‐excitation is achieved in a cylindrical vessel filled with approximately 2 m3 of liquid sodium which can reach flow velocities up to 20 m/s. The main experimental results on the kinematic and the saturation regime are compared with numerical modelling. Some focus is also laid on the spectra of the magnetic field and the pressure.