Fritz Krause (1927–2024)

Fritz Krause came from the early mathematics school in Jena and attended physics lectures by Friedrich Hund. After completing his doctorate, he joined Max Steenbeck at the nearby Academy Institute for Magnetohydrodynamics in 1958, where he developed the mathematical foundations of the dynamo theory of cosmic magnetic fields. The publication “Berechnung der mittleren Lorentz-Feldstärke <u' × B'> für ein elektrisch leitendes Medium in turbulenter, durch Corioliskräfte beeinflußter Bewegung” with M. Steenbeck and K.-H. Rädler in Zeitschrift für Naturforschung in 1966 was by far the internationally most successful journal publication in the history of science in the GDR.

Krause arrived at the Friedrich Schiller University in Jena at the age of 18 as a result of the events of the WW2. Born the youngest in Groß Särchen in Niederlausitz, which is now part of Poland, the Krauses had to leave their homeland in 1945 and reached Friedrichroda in Thüringen as a refugee family. Fritz studied mathematics in Jena from as early as 1946, although he was allowed to take his university entrance qualification retrospectively in the second year at a special FSU institution. Becoming a biologist was another unrealized career aspiration which remained present in many of his later hobby activities. He completed the mathematics degree in 1951 under Walter Brödel, in whose Institut für Reine Mathematik he also wrote his dissertation “Zur konformen Geometrie der dreifachen Orthogonalsysteme.” In 1958, the year he graduated, Irmgard Schröder and Fritz Krause started a family, which soon included their sons Matthias und Peter.

After a brief period as director of the Geomagnetisches Institut der Akademie der Wissenschaften zu Berlin on Potsdam/Telegraphenberg, Krause became head of the “Kosmische Magnetfelder” department at the Astrophysikalisches Observatorium Potsdam, later at the Zentralinstitut für Astrophysik, where hydrodynamic and thermodynamic applications were also developed. The original German-language publications from Jena were translated into English by P. H. Roberts and M. Stix soon after they appeared and have since become one of the cornerstones of the new scientific branch of dynamo theory. Some of the terms introduced at that time, such as α effect or helicity, are still used today in modern publications. Together with K.-H. Rädler, he wrote the widely acclaimed monograph “Mean-field magnetohydrodynamics and dynamo theory” in 1980, the Observatory's first book publication since the end of WW2. In the 70s, we were often visited by Paul H. Roberts from University of Newcastle upon Tyne—who could hardly be beaten at table tennis—also in order to break through the isolation of the Potsdam staff. That also was the time when both were involved in ongoing scientific disputes as a team. The first international conference on the Telegraphenberg for decades, “Stellar and planetary magnetic fields” in 1983, was a final stage in the observatory's rebirth—although the AOP disappeard shortly afterwards as a result of intransparent decisions from the outside.

At the new workplace in Sternwarte Babelsberg, the stellar physics aspect of the dynamo group was lost, partly because the Max Planck Institute for Radio Astronomy in Bonn was currently carrying out sensational measurements of magnetic fields on a large scale. “At last we now can see the toroidal fields we have always talked about,” exclaimed Krause at the 1988 workshop on “Magnetic fields in galaxies” in Babelsberg, which was organized jointly with Richard Wielebinski's group in Bonn. The galactic magnetic fields and their symmetries—axisymmetric or non-axisymmetric—became the preferred testing objects of the global dynamo community at this time. Their observations and theories also dominated the IAU Symposium No. 157 “The cosmic dynamo,” which Krause organized virtually by himself and which was terminated to coincide with the 100th anniversary of the death of the inventor of the dynamo principle, Werner von Siemens. It was the first major event worldwide dedicated solely to the self-excitation of large-scale cosmic magnetic fields and was the first to unite Krause's various circles of scientific friends without any political restrictions.

In one of his last publications in retirement, which he reached with this conference in 1992, Krause attacked one of the most neglected problems of dynamo theory. The magnetic quadrupole solutions observed in galaxies require tiny seed fields of the same symmetry for self-excitation but their generation by contraction in the vertical direction is difficult to imagine.

On his 80th birthday, the Leibniz-Institut für Astrophysik Potsdam honored Fritz Krause—also a member of the Deutsche Akademie der Naturforscher Leopoldina since 1980—with a special colloquium with main contributions by R. Beck (Bonn), J. Kurths (Berlin), and F. Stefani (Dresden-Rossendorf). He spent the last years of his life in the Seniorenresidenz St. Elisabeth in Wilhelmshorst, where he died surrounded by his family shortly before reaching the age of 97.

Günther Rüdiger