Dr. Frank Stefani

Head Geo- and Astrophysics
Phone: +49 351 260 3069


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 gives an impression of the finalized building. A scheme of planned experiments is shown in Figure 2.

Figure 1: The DRESDYN building at HZDR. (a) External view with the left wing (LW) with workshop, chemistry lab and control room, the central hall (CH) for sodium experiments, the right wing (RW) for technical installations and the cleaning station (CS) for sodium-spoiled parts. (b) Interior of the central hall.

Figure 2: Interior of the central hall, and the main planned experiments. Precession driven dynamo experiment (P) to be installed in the containment; Tayler-Couette experiment for the investigation of the magnetorotational and the Tayler instability (M); sodium loop (L); In-Service-Inspection experiment (I). A further stand for testing liquid metal batteries, which is not completely specified yet, will complement the list of sodium experiments.

The most ambitious installation in the framework of DRESDYN is a precession driven dynamo experiment (Figure 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 600 rpm, and around an inclined axis with up to 60 rpm. 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 3: Design of the precession 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 MRI/TI experiment: Magnet for axial field (M); Central rod for azimuthal field (R); Inner cylinder (I); outer cylinder (O).

Besides its astrophysical background, the TI may also be of relevance for a much more earthly application (Figure 5). This is related to large-scale liquid metal batteries which are promising to become cheap means for storing the highly fluctuating electric energy from solar and wind power. While utilizing the economies of scale, the increasing current of such batteries will become prone to the TI, which in turn may destroy the stratification of the light anodic material (Mg,Li,Na), the thin electrolyte, and the heavy cathodic material (Pb,Sb,Bi). Various measures to prevent the TI, which have been developed at HZDR, will be tested in a large-scale battery experiment.

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

Further experiments will be devoted to the development of measuring techniques for various thermohydraulic applications of liquid sodium.