Christof Litwin

Abstract

Christof Litwin, a theoretical physicist with interests ranging from field theory to plasma physics and astrophysics, died 4 October 2001 in Chicago, Illinois, from complications arising from surgery for oral cancer. Christof was a senior scientist in the University of Chicago’s department of astronomy and astrophysics. Born in Lodz, Poland, on 15 June 1949, Christof immigrated to Copenhagen, Denmark, in 1968, both to escape the anti-Semitism then prevalent in Poland and to pursue higher education. In 1972, he received his Part I degree (roughly equivalent to a bachelor’s degree in the US) in mathematics and physics from the University of Copenhagen. In 1976, he received his Cand. Scient., the Danish equivalent to a PhD, in theoretical physics from the Niels Bohr Institute for Astronomy, Physics, and Geophysics. His thesis, an early contribution to string theory, was entitled “Dual Strings and Membranes.”Christof worked on particle physics at SLAC from 1977 to 1980, but then switched fields as his interests evolved toward collective phenomena. He joined Cornell University in 1980 as a research associate. There, with Ravi Sudan, he investigated a range of plasma problems, including plasma turbulence and the stability of both the spheromak magnetic confinement configuration and tandem mirrors. Christof was named a NATO fellow in science (1977–79).In 1984, Christof joined the University of Wisconsin-Madison as a research scientist in the department of engineering physics to work on tandem mirrors; Christof later extended his interests to include toroidal systems. At Wisconsin, he worked out the effect of the ponderomotive force on the macrostability of plasma. He will be remembered for linking macroscopic plasma behavior to microscopic turbulence, demonstrating theoretically that certain microinstabilities could spontaneously stabilize largescale magnetohydrodynamic instabilities. He explained how ion cyclotron instabilities, driven by anisotropic ion temperatures, could arise in tokamak plasmas and stabilize the puzzling sawtooth instabilities seen on the world’s largest tokamaks. Christof also hypothesized that alpha particles in a magnetic mirror plasma undergoing fusion could excite velocity-space instabilities that in turn could stabilize interchange instabilities. Christof’s work significantly influenced other experiments. For example, in 1993, at Wisconsin, he pointed out that the experimental effort for searching for a dynamo effect to drive current in a tokamak was flawed, and instead suggested a Landau-resonant current drive. He devised models to infer the location of the wave-driven current from experimental measurements of the loop voltage response and showed how lower hybrid waves could generate current to suppress magnetic turbulence in the reversed field pinch plasma configuration. As a result, the Wisconsin experimental efforts shifted to the directions Christof considered most promising.Still at Wisconsin, Christof became a visiting associate professor in the department of nuclear physics at the Weizmann Institute of Science in Rehovot, Israel, from 1989 to 1991. His visit turned out to be critical in unexpected ways: There he met his wife-to-be and also made a transition to plasma astrophysics. After explaining fluctuations and transport in the magnetically insulated diode experiments carried out by Yizhak Maron, Christof worked out the consequences of laboratory-based transport theory for the solar corona. This theory sought to explain the corona’s highly structured magnetized atmosphere. In 1990, Christof was awarded a Dr. Scient. at Copenhagen, a special degree recognition beyond the PhD, without an equivalent in the US.In 1993, in a landmark paper in the Astrophysical Journal, Christof provided a general framework for treating transport in the corona. After moving in 1997 to the University of Chicago, Christof was in the midst of an extraordinarily productive phase of his research in plasma astrophysics, having made important contributions to understanding the stability of accretion columns on neutron stars, the penetration of accreted plasma into the magnetosphere of compact stars, and the acceleration of ultrahigh-energy cosmic rays due to cometary or asteroidal impacts in the magnetospheres of neutron stars, when his life was cut short.While he was hospitalized in October 2001, Christof was actively engaged, as usual, in a wide variety of calculations, including treatment of magnetic stochasticity on Alfvèn wave propagation and current drive in laboratory plasmas, and new computations of the propagation of ultrahigh-energy cosmic rays in the intergalactic medium. He had even set up his computer in the hospital room, and was busy answering his e-mail.The impact that Christof made on his scientific world went far beyond the natural conundrums. Those of us who worked closely with him could not help being drawn to his attitude, his gentle wisdom, his inquisitive and questioning spirit, and his focus on what was hard and novel. Christof, who learned six languages and was articulate and widely informed, will be remembered as a thoroughly enjoyable and brilliant physicist with infectious enthusiasm. We miss him deeply. Christof Litwin PPT|High resolution© 2002 American Institute of Physics.