the European Union (EU), and Japan to undertake joint design of a tokamak experimental reactor. This design provided the early foundations for the current ITER project.
By the mid-1990s, two tokamak devices achieved the generation of controlled fusion power of more than 10 megawatts for a period on the order of several seconds. The devices were the Tokamak Fusion Test Reactor (TFTR) in Princeton, New Jersey, and the Joint European Torus (JET) in the United Kingdom. The experimental milestones achieved at these facilities in the confinement, heating, and control of the plasma and the first use of tritium fuel were significant. Scientifically a critical finding was that the energetic helium ions produced by the deuterium-tritium (D-T) fusion reaction were well confined and behaved as expected; that is, they “gave back” essentially all their energy to the plasma itself. These experiments provided the technical and scientific confidence that a burning plasma could be achieved in a next-generation device, the device currently designated as ITER. In such “burning plasma” devices the 20 percent of the energy generated by the fusion reactions found in the He ions mentioned above is used to maintain the necessary high temperatures—that is, the fusion reactions will self-heat and sustain the plasma. This is the fundamental feature of an energy-producing tokamak plasma that will be found in fusion reactors, but not in present devices.
Although the United States was one of the original ITER partners, in 1998 Congress ordered DOE to withdraw from the international collaboration. In spite of the U.S. withdrawal, partners in Europe, Russia, and Japan continued to advance the design of the project. These efforts, although they resulted in a slight descoping of technical objectives, led to the present ITER design that provides access to burning plasma regimes at a reduced cost. In parallel, the U.S. fusion community held a series of workshops that demonstrated broad support for advancing a burning plasma experiment. Several burning plasma options were examined, and the U.S. community gave the new ITER design a favorable technical assessment. The community also noted that the ITER project had adopted changes advocated by the United States. Motivated by the renewed prospect of a positive next step in magnetic fusion research, in 2002 the DOE Fusion Energy Sciences Advisory Committee voiced its support for a renewal of U.S. participation in ITER negotiations. Similarly, the U.S. National Research Council’s Burning Plasma Assessment Committee in its 2002 interim letter report reaffirmed this recommendation to rejoin talks and stated in its subsequent full report that “the U.S. fusion program, after many years of research, is poised to take a major step toward its energy goal. It is clear that a burning plasma experiment is a necessary step on the road to fusion energy and of scientific and technical interest to the U.S.