Contact

Dr. Frank Stefani

Head Geo- and Astrophysics
f.stefaniAthzdr.de
Phone: +49 351 260 3069

DRESDYN

The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) is an infrastructure project devoted both to large scale liquid sodium experiments with geo- and astrophysical background, as well as to investigations of various energy related technologies. Figure 1 shows a photograph of the building.

Figure 1: The DRESDYN building at HZDR. External view with with workshop, chemistry lab and control room in the left wing, and the central hall for sodium experiments. The right wing houses technical installations, e.g. transformers, the argon extinguishing facility and air cooling.

Precession driven dynamo

The most ambitious installation in the framework of DRESDYN is a precession driven dynamo experiment (Figures 2 and 3), which aims at clarifying whether precession could be a viable source of planetary magnetic fields. Basically, it consists of a liquid sodium filled container of 2 m diameter, with a central cylinder of 2 m height and two conical end pieces, rotating around its central axis with up to 10 Hz, and around an inclined axis with up to 1 Hz. Depending on the precession ratio, and on the angle between the rotation and the precession axis, different flow structures appear and will be tested with respect to their suitability for magnetic field self-excitation.

Figure 2: Design of the precession experiment.
Figure 3: Photograph of the precession experiment.

In November and December 2024, first water experiments were carried out with a rotation rate of 1 Hz and a precession rate of up to 0.1 Hz (see video). Transitions between laminar and turbulent flow regimes were detected at the expected precession ratio.

Download video/mp4 - 43,8 MB / 1920x1080 px
Video: Movie of the first water experiments with a rotation rate of 1 Hz and a precession rate of 0.1 Hz.

MATISSE (MAgnetically Triggered flow Instabilities in disks and Stars: A Sodium Experiment)

The goal of a second experiment (Figure 4) is to study various combinations of the magnetorotational instability (MRI) and the Tayler instability (TI). The MRI is widely believed to trigger turbulence and angular momentum transport in accretion disks around protostars and black holes, thereby allowing mass concentration onto these central objects. The TI is thought to play a role in the angular momentum transport in neutron stars, and is also discussed as a key ingredient of an alternative stellar dynamo model, the Tayler-Spruit dynamo. After having investigated the helical and the azimuthal MRI, as well as the pure TI in much smaller experiments with the eutectic alloy GaInSn, the new liquid sodium experiment will allow to studying the combinations of these instabilities, as well as the standard version of MRI.

Figure 4: Design of the MATISSE experiment.

In addition to its astrophysical significance, TI may also play an important role in a ‘terrestrial’ application (Figure 5). This involves large-scale liquid metal batteries, which are being discussed as promising storage systems for highly fluctuating renewable energies. As the cost per stored kilowatt hour decreases with increasing battery size, the aim is to maximise the size of the battery from an economic perspective. However, this results in currents in the battery at which the TI starts in the form of vortices, which can destroy the stable layering of the anodic material (Mg, Li, Na), the thin electrolyte and the cathodic material (Pb, Sb, Bi). Various measures developed at the HZDR to suppress TI are to be validated in a special test stand.

Figure 5: The current-driven Tayler instability can play a detrimental role for the stability of large-scale liquid metal batteries.

Further experiments within the DRESDYN programme are dedicated to the development of measurement techniques for thermohydraulic applications of liquid sodium.


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