About the Jenko Group
If driven sufficiently hard, flows in fluids, gases, or plasmas become turbulent. This phenomenon is quite ubiquitous. E.g., the quest for understanding the origin of planetary, stellar and cosmic magnetic fields, the development of better aircrafts or automobiles, and many questions raised in atmospheric and ocean physics are all intimately related to turbulent dynamics. From a fundamental point of view, turbulence is a paradigmatic example of nonlinear dynamics in open systems with many degrees of freedom. Here, the system typically establishes a quasistationary state far from thermodynamic equilibrium. For this to happen, a permanent input, redistribution, and output of energy is required. Turbulence is often described as a bath of vortices of varying sizes and lifetimes, sometimes spanning several orders of magnitude, and all of them nonlinearly created, coupled, and destroyed. But none of the established theories based on statistical mechanics is able to capture this peculiar state somewhere between order and disorder. It undoubtedly belongs to the most important unsolved problems of classical physics.
One important frontier of turbulence research is to understand the turbulent dynamics in plasmas (ionized gases). In contrast to our immediate environment on Earth, the vast majority of the visible Universe is known to be in this "forth state of matter." In particular, the space between planets, stars, and galaxies tends to be filled with plasma. Thus, not surprisingly, some of the most pressing questions in space science and astrophysics are closely linked to our grasp of plasma turbulence. This includes key open questions like: Which processes are responsible for heating the solar corona to millions of degrees? What is the origin and role of the omnipresent magnetic fields in our Universe? How does matter accrete onto the massive black hole in the center of our galaxy? Which natural accelerators are able to produce cosmic rays with energies of more than 100 EeV (i.e., about 10 million times more than what we can achieve with the Large Hadron Collider at CERN). - Many very good reasons to explore the physics of turbulent plasmas!
Another key driver for plasma turbulence research is the quest for fusion energy, a safe, sustainable, and environmentally friendly option to cover the further increasing global energy needs for generations to come. Fusion is the process which powers the stars and enables life on Earth. The idea is to mimick this process by heating a mixture of deuterium and tritium (two heavy versions of hydrogen) to extremely high temperatures of more than 100 million degrees, and keeping the resulting plasma away from the material wall (for the benefit of both the plasma and the wall) with the help of a doughnut-shaped "magnetic cage." Unfortunately, turbulent processes significantly reduce the energy confinement time, an effect which can only be compensated by building bigger, more expensive machines. Thus a key challenge on the road to efficient fusion power plants is to understand, predict, and control turbulence. The success of ITER - the world’s flagship project in fusion research, currently under construction in Southern France - hinges on such advances in plasma science. This makes the study of plasma turbulence a very rewarding endeavor with great societal impact.
Motivated by the study of fundamental physical processes in laboratory and natural plasmas, which tend to involve nonlinear interactions between many degrees of freedom covering a wide range of spatio-temporal scales, one is lead to also consider other complex systems, from planetary atmospheres to dense bacterial suspensions. Often, insights, concepts, or tools developed in one application area can be transferred to another one, allowing for cross-fertilization and the development of a unifying view on seemingly disparate fields of science. Examples include the origin and nature of non-universal power laws and non-Gaussian transport. Moreover, progress in these areas of complex systems research is often deeply connected with our ability to solve the underlying nonlinear partial differential equations with the help of supercomputers. Therefore collaborative links to colleagues from Applied Mathematics and Computer Science are invaluable in this context. These are reflections of the markedly interdisciplinary character of the kind of research pursued in our group.