The Riga Dynamo Experiment
Magnetic fields of planets, stars, and galaxies are produced by the motion of electrically conducting fluids. While the corresponding theory of hydromagnetic dynamos has been widely elaborated in the last decades, an experimental verification of magnetic field self-excitation in conducting fluids was missing until recently. Besides a few other experimental approaches in the world, the Riga dynamo facility is one of the large sodium facilities devoted to the investigation of this phenomenon.
Figure 1 shows a sketch and photograph of the facility, whose central module (Figure 2) comprises a propeller driven central helical flow (with a velocity up to 20 m/s), a straight back-flow and sodium at rest in additional coaxial tubes of stainless steel. In order to reach self-excitation with the limited power resources, the whole facility had been optimized in a long iterative process of pump design and numerical simulations. Figure 2 shows also a snapshot of the expected magnetic field resulting from our 2D-solver for the induction equation.
In November 1999, first dynamo experiments were carried out. After having studied the pure amplification of an externally applied 1Hz magnetic field for various propeller rotation rates, an additional exponentially growing eigenmode with a frequency of 1.3 Hz appeared at the highest rotation rate of 2150 rpm (Figure 3). Unfortunately, this campaign had to be stopped due to a technical problem, so that the saturation regime of the dynamo could only be reached in the next campaign in July 2000 (Figure 4).
In Figure 5 we compile the growth rates (a) and the frequencies (b) of the eigenfield measured in a number of campaigns between 1999 and 2007, showing in general a very good agreement with our numerical simulations. After repair and recommissioning in 2016, the Riga dynamo experiment is now ready for further measurement campaigns.
Publikationen:
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Gailitis, A., Lielausis, Dement'ev, S., Platacis, E., Cifersons, A., Gerbeth, G., Gundrum, Th., Stefani, F., Christen, M., Hänel, H., Will, G.
Detection of a flow induced magnetic field eigenmode in the Riga dynamo facility
Phys. Rev. Lett. 84 (2000), 4365-4368 -
Gailitis, A., Lielausis, O., Platacis, E., Dement'ev, S., Cifersons, A., Gerbeth, G., Gundrum, Th., Stefani, F., Christen, M., Will, G.
Magnetic Field Saturation in the Riga Dynamo Experiment
Phys. Rev. Lett. 86 (2001), 3024-3027 -
Gailitis, A., Lielausis, O., Platacis, E., Gerbeth, G., Stefani, F.
Laboratory Experiments on Hydromagnetic Dynamos
Reviews of Modern Physics 74 (2002), 973-990 -
Gailitis, A., Lielausis, O., Platacis, E., Gerbeth, G., Stefani, F.
The Riga dynamo experiment
Surveys in Geophysics 24 (2003), 247-267 -
Gailitis, A., Lielausis, O., Platacis, E., Gerbeth, G., Stefani, F.
Riga dynamo experiment and its theoretical background
Phys. Plasmas 11 (2004), 2838-2843 -
Gailitis, A., Gerbeth, G., Gundrum, Th., Lielausis, O., Platacis, E., Stefani, F.
History and results of the Riga dynamo experiment
Comptes Rendus Physique 9 (2008), 721-728 -
Stefani, F., Gailitis, A., Gerbeth, G.
Magnetohydrodynamic experiments on cosmic magnetic fields
Z. Angew. Math. Mech. 88 (2008), 930-954 -
Stefani, F., Gailitis. A., Gerbeth, G.
Energy oscillations and a possible route to chaos in a modified Riga dynamo
Astron. Nachr. 332 (2011), 4-10 -
Gailitis, A., Gerbeth, G., Gundrum, Th., Lielausis, O., Lipsbergs, G., Platacis, E., Stefani, F.
Self-excitation in a helical liquid metal flow: The Riga dynamo experiments
Journal of Plasma Physics 84 (2018), 735840301