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discovered_01_2013

discovered 01.13 FOCUS WWW.Hzdr.DE In other words, during development, we’re constantly monitoring several very sensitive topics where we’re charting new territory. How do you get the building ready for the great dynamo experiment and what will it cost? _PK . The new building will combine a number of functions. For one, we have an experimental hall with capabilities for different types of experiments that are not really critical in terms of safety. As far as safety goes, the precession experiment does occupy a special place. For safety reasons, we need to enclose the machine inside a protective containment and assume that this will help ward off mechanical threats and protect against fires. The HZDR’s building department helps out with technological construction equipment; it ensures that the overall infrastructure like the power supply, climate, or cooling is safe and functional and protects against fires. For the scientists, however, the hall with its different experiments is the main focus. _FS . Besides the containment, we’re investing in a very elaborate argon fire extinguishing system, which would allow us to fill the containment within two minutes’ time to extinguish a potential sodium fire. This extinguishing system also covers the deeper lying sodium storage tanks. The containment is on the ground floor. The dynamo it contains works on its own separate foundation, supported by seven posts that reach 22 meters below the surface of the Earth. Construction of the building is projected to cost around eight million Euros, the dynamo itself seven million. The projected total budget is 23 million and that should just about cover it. We hope that we will also be able to use external funds for the applied topics. By the way, sodium is not expensive and you can get it for as little as two Euros per kilo. In other words, liquid sodium is the brace which holds all the various experiments at the DRESDYN facility together? _FS . Yes, and if you look closely, it’s actually hidden in the acronym DRESDYN, which stands for DREsden Sodium facility for DYNamo and thermohydraulic studies. The deeper lying tanks are storing some twelve tons of sodium that will be apportioned for the various experiments. With DRESDYN, we want to bring our geophysical and astrophysical experiments under one roof and continue to advance them. After all, sodium is the sole liquid metal that allows us to realize this goal with a reasonable technological and financial effort. One example I would like to mention is a combined experiment designed to help us find answers to many unanswered questions about two important magnetic instabilities: the magnetorotational and the Tayler instability. Both of these are important phenomena in the cosmos, and basically we were successfully able to confirm both of them in the lab: The magnetorotational instability in the framework of the PROMISE experiment back in 2006 and, more recently, the Tayler instability in a current-carrying liquid metal column. Now, for the first time ever, we’re planning on studying both instabilities at the same time as part of the new experiment. We just submitted a theory-based work on this showing that the combination of both effects could prove extremely important to the development of turbulence in the relatively poorly conducting areas of protoplanetary disks or of accretion discs that feed black holes. Yet our understanding of the pure magnetorotational instability is far from comprehensive. It is our hope that we might advance into the area of the standard version, starting from the "helical" version we’re already familiar with from PROMISE. The key ingredients for this are sodium, a strong field, and real "speed." The planned experiment will consist of an inner and outer cylinder, each approximately two meters tall, with roughly one ton of sodium between them that will be set into differential rotation. Currents of several thousand ampere each are sent through an isolated copper rod at the center and also through the sodium itself. This way, we will simultaneously juggle five parameters and thus do a lot of very exciting astrophysics. This is what we’re working on together with our colleagues from the Leibniz Institute for Astrophysics in Potsdam and the ETH in Zurich. Applied research won’t get the short end of the stick either. In close collaboration with the French Atomic Energy Agency CEA, we’re planning what’s known as an "in-service inspection" experiment to test measuring techniques for these types of flow phenomena as they will be occurring in the new, sodium-cooled fast reactors in France. My HZDR colleagues are also interested in sodium-based turbulence studies and in two-phase flow. A new addition in the last two years is the topic of liquid metal batteries. As long as you make them large enough, they could potentially serve as economically feasible storage sites for renewable energies. However, it turns out that with these kinds of large-sized batteries, our Tayler instability would occur and potentially ruin the liquid parts’ stratification. In a special test facility, we want to examine how we might be able to suppress this and other magnetohydrodynamic instabilities in large liquid metal batteries. In particular, it is this close proximity of astrophysical research and applied battery research, both in terms of content and location, which makes DRESDYN so appealing to me. Mr. Stefani, as a scientist you’re in charge of the experiments, and you, Mr. Kaever, are head of research technology at the HZDR. What exactly does your collaboration look like or rather what makes it so special? _PK . From the perspective of research technology, DRESDYN is a very special project since a lot of the technical engineering contents have to be clarified with our external

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