At this moment, the National Ignition Facility (NIF) is preparing to come online at Lawrence Livermore National Laboratory in California (see the New York Times story). The goal of NIF is to study small-scale nuclear fusion ignited by a precisely focused array of 192 high-power lasers. Reflecting a situation often seen in higher profile with America’s space program, the project is vastly over-budget, and its worth has been subjected to extensive criticism. Nuclear fusion has for decades remained a subject of intensive study and perpetually unmet promise. The “Array of Contemporary American Physicists” on which I am now at work for the AIP History Center will have fusion and related plasma research as one of its focuses, and includes information on some of those involved in the NIF as well as in prior generations of research.
Lyman Spitzer explains the “stellarator” at the Second Geneva Conference on the Peaceful Uses of Atomic Energy, 1958
The study of nuclear fusion dates to the 1930s, when an emerging theoretical understanding of subatomic forces and particles suggested a way of accounting for the energy produced by stars and the synthesis of elements within them, as worked out by German émigré physicist Hans Bethe. During World War II, it was understood that artificial fusion could be created by using a fission bomb to ignite nuclear fuel—the idea behind the “super” or “hydrogen” bomb. This possibility was pursued during the war by Hungarian émigré physicist Edward Teller, and, following debate on whether it should be done, was pursued by researchers and engineers at Los Alamos Scientific Laboratory, resulting in the October 1952 test at Eniwetok atoll, and, ultimately, subsequent generations of thermonuclear weapons.
However, scientific understanding of fusion processes and the behavior of super-hot, highly ionized gas, or “plasma”, was still extremely rudimentary, prompting the establishment of a series of classified research programs under Atomic Energy Commission (AEC) auspices codenamed Project Sherwood. These were located at Los Alamos, the then-new Livermore national weapons laboratory, and Princeton University. Obtaining this information would be necessary to produce controlled nuclear fusion.
To control nuclear fusion means to subject nuclear fuel (unlike fission, generally a light element, such as an isotope of hydrogen) to intense energies within a confined space, and to keep them out of contact with objects that would cause them to lose energy, notably the walls of said confined space. To do this, it would be necessary to use magnetic fields to contain the plasma and to prevent it from coming into contact with its container. In particle accelerators this sort of effect is accomplished for individual particles—free electrons and protons. Plasmas, however, are effectively net neutral fluids, which exhibit peculiar properties, especially in magnetic fields, making their control more challenging.
In 1950, the astrophysicist Lyman Spitzer, Jr. was already studying interstellar plasmas and was privy to discussions of nuclear fusion taking place around the United States’ hydrogen bomb project through his Princeton colleague John Wheeler. Wheeler was involved in the bomb research and was establishing a satellite research facility in Princeton, which Spitzer suggested be named Project Matterhorn. Inspired by an unscrutinized report of fusion energy research results in Argentina, Spitzer proposed to the AEC an “8”-shaped fusion reactor, which he called the “stellarator”, designed to overcome forces that would separate the charged particles constituting the plasma from each other. This device would go on to form the basis of fusion research at Princeton in the 1950s.
Spitzer was enthusiastic that fusion energy could quickly be made practical, but this enthusiasm was not universal, even among other fusion researchers—British physicist James Tuck’s group at Los Alamos named their first apparatus the “Perhapsatron”. Nevertheless, AEC chairman Lewis Strauss was eager to push the contained fusion project to best foreign competitors, and provided ample funding to Project Sherwood, though still small in comparison to weaponry development and fission research. At Princeton, while the stellarator failed to provide a path to usable fusion energy, it did help kick start research into the behavior of plasma: the “magnetohydrodynamic” model of plasma stability developed by Project Matterhorn theorists Ira Bernstein, Edward Frieman, Martin Kruskal, and Russell Kulsrud was an influential early result.
At the insistence of Strauss, early fusion research was classified. However, with mounting pressure from researchers, Project Sherwood was declassified in 1958 as part of the international diplomatic effort then being built around the “Peaceful Uses of Atomic Energy”. Once it was revealed that projects in Britain and the Soviet Union had also experienced severe difficulties in the pursuit of contained fusion, a new air of sobriety set in over fusion research. It was now suggested that the multipronged development of the 1950s had proceeded without a sufficient theoretical understanding of plasma behavior, and thereafter “basic” research proceeded on a wide variety of plasma phenomena.
The new emphasis now drove a wedge between fusion research and plasma research, as the complex behaviors created by many competing phenomena existing in fusion apparatuses proved unamenable to study. At Princeton, to the chagrin of Spitzer, researchers such as Francis Chen, now used devices such as the “L-1”, “L-2” and “Q” machines, which were designed to produce more isolated phenomena, but which would not provide a direct path to a fusion reactor. It was at this time that Project Matterhorn was renamed the Princeton Plasma Physics Laboratory (PPPL). In the 1970s, fusion research (now including laser-ignited fusion) and plasma research reunited as plasma behaviors under “extreme” conditions became of interest, and a renewed enthusiasm for alternative sources of energy in the face of that decade’s energy crisis multiplied funding. PPPL remains a government facility and a key center for plasma and fusion research.
An early historical study of fusion research including the work at Princeton is Joan Lisa Bromberg’s Fusion: Science, Politics, and the Invention of a New Energy Source (1982). A recent and deft encapsulation and characterization of fusion and plasma research between 1950 and 1980 is “Properties and Phenomena: Basic Plasma Physics and Fusion Research in Postwar America” by physicist Gary Weisel in Physics in Perspective 10 (2008): 396-437. Princeton University Library has made the early Project Matterhorn reports available online. The AIP Niels Bohr Library and Archives has a transcript of a 1978 interview between Bromberg and Spitzer online.