Dieter Joseph Sigmar died in Austin, Texas, on 31 July 2005 after a lengthy and courageous battle with multiple sclerosis. During his long and productive career, he played a key role in the US and international magnetic-fusion energy and plasma-science programs.
Dieter was born in Vienna, Austria, on 11 April 1935. He received his undergraduate degree in physics in 1960 from the Technical University of Vienna. After receiving his PhD in nuclear physics there in 1965, Dieter spent four years as a staff scientist at Oak Ridge National Laboratory (ORNL). He then went to MIT in 1970 as a postdoctoral fellow working with Bruno Coppi in the physics department and stayed on as an associate professor in the nuclear engineering department until 1976. While at MIT, Dieter did seminal work on collisional transport theory in tokamaks, including a classic review article with Steven Hirshman on the role of impurities. Collisional transport remained his interest even after his retirement and is the subject of the superb textbook Collisional Transport in Magnetized Plasmas (Cambridge U. Press, 2002), which he coauthored with Per Helander.
For the next nine years he worked at ORNL, where he became the associate head of theory. He returned to MIT in 1985, where he served at various times as head of theory, acting director, and deputy director of the Plasma Science and Fusion Center while maintaining his ties to the nuclear engineering department.
At ORNL and then as theory head at the PSFC, Dieter pursued his interest in the role of alpha particles in burning tokamak plasmas. He made important contributions to the understanding of collisional transport in tokamaks and the behavior of alpha particles in fusing plasmas. He incited the national and international fusion communities to focus their attention on stability and transport issues associated with fast particles, and he urged experimentalists to develop techniques for observing alpha-related phenomena.
During Dieter’s tenure as acting director of the PSFC, he realized that the US edge-physics program needed strengthening because of the increasingly important role of the edge region and the need for a divertor at the edge of a tokamak reactor to handle the heat load. He responded by establishing a divertor physics program at the PSFC and subsequently was appointed by the US Department of Energy to head the US divertor task force. His work and the work of other members of that task force provided many new insights into our present understanding of divertor operation and developed important capabilities in the numerical modeling of divertors.
Both the alpha-particle and divertor research efforts at the PSFC led to productive collaborations in the international fusion community. Those research endeavors are now considered crucial aspects of the current US and world fusion programs as they head toward their goal of building ITER, the International Thermonuclear Experimental Reactor.
Dieter helped develop and maintain a superb theory program at MIT, one that has made many outstanding contributions to magnetic-fusion energy research, and he enhanced the visibility of the PSFC and its Alcator C-Mod experimental program in the international fusion community. Dieter retired from MIT in 2001 because of ill health. Upon his retirement, DOE recognized his efforts on behalf of magnetic fusion by presenting him with a Distinguished Associate Award.
Dieter was appointed A. O. Professor of Plasma Physics at the Technical University of Vienna in 1981 and was elected a corresponding member of the Austrian Academy of Sciences in 1996. He established theory exchanges between MIT and both Chalmers University of Technology in Sweden and the Culham Laboratory in England, and he fostered US collaboration with Russian and Japanese scientists. As a result of his pioneering work on alpha-particle theory, Dieter served on the deuterium– tritium program advisory committee of the Princeton Plasma Physics Laboratory’s Tokamak Fusion Test Reactor and was a co-organizer of an international alpha-particle workshop. He served on many other DOE committees, including the theory coordinating committee and the US ITER steering committee. He was a member of the board of editors for the plasma physics journals Nuclear Fusion (10 years) and Physics of Fluids (4 years), and helped organize several national and international meetings.
While Dieter’s many scientific contributions to fundamental plasma theory are well documented and heralded, his personal impact on shaping the intellectual lives of the next generation of plasma theorists was equally important. Dieter had an unsurpassed knack for arousing intellectual curiosity in his peers and the ability to passionately stimulate the pursuit of knowledge to achieve a deeper level of understanding. He was, at his core, a deeply caring individual. It was this dual aspect of his personality—a keen intellect tempered by a genuine concern for people—that made Dieter a unique individual who will be deeply missed by all who were fortunate enough to have known and worked with him.
