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discovered_01_2016

WWW.HZDR.DE 32 33 PORTRAIT // THE HZDR RESEARCH MAGAZINE will therefore be a unique opportunity for the theoretician to build bridges between astrophysics, which tends to use simulations, and experimental fluid dynamics. For this purpose, he wants to investigate MRI under preconditions the theoretical analyses have neglected up to now. "They assume a higher degree of stability," Mamatsashvili explains. "But that doesn’t correlate with the actual conditions in the disks, which are presumably much more instable." Reasearchers most often use the so-called modal approach for studying MRI. "This assumes that in the long run, turbulences will either drop or grow exponentially, but their behavior at the outset is not taken into account. This means that even flows that should really be stable in the long term are instable from the start." For his analysis, George Mamatsashvili therefore wants to use the non-modal approach, which factors in this process. "Various studies have shown that non-modal growth of MRI can be much stronger than the modal one so that the conditions for the formation of turbulences don’t have to be as stringent as we had thought so far." HZDR Research Award for Controlled Spin Waves Up to now, the number of transistors per microprocessor has doubled roughly every two years. But the limits of ever smaller processors with ever higher performance are gradually being reached. One of the main reasons is the amount of waste heat generated when yet more circuits are squeezed onto an increasingly small surface. The Magnonic Junior Research Group around Helmut Schultheiß is trying out a new approach based on spin – the magnetic angular momentum of electrons. In ferromagnetic materials, this makes it possible to generate spin waves, which can transport information like flowing charge carriers, but without the extreme waste heat. For the very first time, Helmut Schultheiß, Andreas Henschke, Thomas Sebastian and Kai Wagner managed to control the emission of spin waves on the nano-scale. To do so, they transmitted a wave through a domain wall – the area where the different magnetic domains meet. For this achievement, they received the HZDR Research Award 2015. New Helmholtz Young Investigators Group An international collaboration of researchers recently managed to directly track the transformation of graphite into a special form of diamond for the first time: Lonsdaleite had previously been a matter of speculation. Only formed under very high pressure, this hexagonal diamond structure does not occur on Earth under natural conditions. In order to investigate the formation process of this alien matter, the researchers combined two high-energy lasers with the free-electron laser at the Linear Coherent Light Source in Stanford. The head of this collaboration, Dominik Kraus, is now joining HZDR, because similar experiments on warm dense matter (WDM) will soon be possible at the Helmholtz International Beamline for Extreme Fields (HIBEF). An international consortium led by HZDR is currently installing these new capabilities at the High Energy Density Facility of the European XFEL. In order to be involved in constructing HIBEF, Kraus has relocated to Dresden. Together with his Helmholtz Young Investigators Group, he wants to explore the fundamental physics of WDM. _Institute of Fluid Dynamics at HZDR Dr. George Mamatsashvili g.mamatsashvili@hzdr.de Dr. Frank Stefani f.stefani@hzdr.de www.humboldt-foundation.de CONTACT With the help of this alternative technique the impact of MRI on the processes in accretion disks can be investigated in much greater detail, Mamatsashvili is confident. He wants to demonstrate this by testing his theoretical outcomes on PROMISE, the Potsdam Rossendorf Magnetic InStability Experiment, a device on which Frank Stefani also conducted his experiments – thus making the connection between simulation and experiments. Dominik Kraus Thomas Sebastian, Andreas Henschke, Helmut Schultheiß (f.l.t.r.; not in the picture: Kai Wagner) receive the 2015 HZDR Research Award from IPP Director Sibylle Günter and HZDR Scientific Director Roland Sauerbrey. Photo: André Forner

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