5 FEBRUARY 1927 * 28 SEPTEMBER 2003
MARSHALL ROSENBLUTH was for forty years one of the leaders of the international community of scientists and engineers trying to develop fusion as a clean and inexhaustible source of energy. In the United States he was the most important fusion theorist. He combined in one person two unusual gifts. He was a master of applied mathematics, with unrivaled ability to analyze the complex patterns of behavior of high-temperature plasmas. He was also an international diplomat, with unrivaled ability to cross barriers of culture and language and build friendships with plasma physicists all over the world. For him, the understanding of plasma physics was not merely an intellectual challenge. The driving force of his life and work was his conviction that the power of hydrogen fusion reactions, the power of the bombs that could destroy cities and civilizations, could also be used in peaceful reactors to bring wealth and prosperity to all mankind.
Rosenbluth was born in Albany in 1927 and was a student of Enrico Fermi at the University of Chicago from 1946 to 1949. As a student at Chicago, he published, together with his student contemporaries C. N. Yang and T. D. Lee, a letter in the Physical Review with the title "Interaction of Mesons with Nucleons and Light Particles," presenting evidence for a universal weak interaction operating with equal strength between light and heavy particles. This one-page letter was an important milestone, pointing the way toward the unified theory of weak interactions that was discovered many years later. During his student days, Rosenbluth also published the first fully relativistic calculation of electronproton scattering. He would certainly have become a leading particle physicist if his attention had not been distracted by plasma physics.
After a year as an instructor at Stanford, Rosenbluth was recruited by Edward Teller to work on the crash program to design a hydrogen bomb at Los Alamos. Unlike Teller, he was a good team player and had the combination of qualities-perseverance, technical skill, and meticulous attention to detail-that the hydrogen bomb program required. He arrived at Los Alamos in time to make major contributions to the design of the first hydrogen bomb, which was exploded in the Mike test of 1952. When Stalin died in the spring of 1953, Rosenbluth decided to leave Los Alamos, but he did not leave immediately. He continued to work on the next generation of bombs, and in 1954 he was present in the South Pacific at the Castle Bravo test, which exploded with a yield of 15 megatons. The Castle Bravo bomb showered Rosenbluth's ship, in addition to the ill-fated Japanese fishing-boat Fortunate Dragon, with radioactive fallout. He said later, "There was a huge fireball with these turbulent rolls going in and out. The thing was glowing. It looked to me like a diseased brain up in the sky. It spread until the edge of it looked as if it was almost directly overhead. It was a much more awesome sight than a puny little atomic bomb. It was a pretty sobering and shattering experience." He then decided that he had had enough of bombs and would devote the rest of his life to the development of peaceful fusion.
Before leaving Los Alamos, Rosenbluth worked with his first wife, Arianna, Nick Metropolis, and Edward Teller on new methods for simulating physical processes with the electronic computers that were then coming into operation. They developed the Monte Carlo method, studying the statistical behavior of atoms and molecules by looking at them one at a time, letting the state of each molecule be determined by random throws of dice. The Monte Carlo method was a profound innovation, moving away from the continuous variables and differential equations that had dominated the physical sciences since the time of Newton. Continuous variables were replaced by discrete events, differential equations by simple counting of events with various outcomes. …