large-scale step in magnetic fusion research and high-temperature plasma physics is to create a burning plasma—one in which alpha particles from the fusion reactions provide the dominant heating of the plasma. The objective of doing so is to understand the physics of the confinement, heating, and stability of a burning plasma as well as to explore the technical problems connected with the development of a power-producing fusion reactor. A burning plasma experiment is a key scientific milestone on the road to the development of fusion power.

The first mildly burning plasma experiments were achieved in the 1990s at the Tokamak Fusion Test Reactor (TFTR) in the United States and at the Joint European Torus (JET) in the United Kingdom. The plasmas in these experiments generated up to 16 MW of fusion power for about 1 s; 80 percent of this power was in the form of 14 MeV neutrons, which escaped from the plasma, and 20 percent was in the form of 3.5 MeV charged alpha particles (helium nuclei) that were confined within the plasma. These alpha particles heat the plasma through Coulomb collisions with the other particles within the plasma—the fraction of transient alpha-particle heating in TFTR was about 5 percent and in JET about 15 percent. Nevertheless, in both cases alpha-particle-induced heating of electrons near the plasma core was clearly measured. These experiments began the exploration of the burning plasma regime.

Several strongly burning plasma experiments have been proposed, including the International Toroidal Reactor (INTOR), the U.S. Compact Ignition Tokamak (CIT), the U.S. Burning Plasma Experiment (BPX), the Italian IGNITOR experiment, the International Thermonuclear Experimental Reactor (ITER), and, most recently, the U.S. Fusion Ignition Research Experiment (FIRE) (see Appendixes C and F for additional information on proposed experiments and fusion reactor concepts). The experimental goal in each of these experiments is to reach a plasma state in which the alpha-particle self-heating is the dominant energy source for the plasma.2 The creation of such plasmas is a necessary but not sufficient condition for the development of a practical energy-producing magnetic fusion power plant.

The study of the science and technology of burning plasmas is a critical missing element in the OFES program. The recent report from the National Research Council’s Fusion Science Assessment Committee (FUSAC)3 noted that experi-

2  

The fusion-produced alpha-particle heating is considered dominant when it is sufficient to strongly impact the plasma pressure and temperature profiles. This occurs when the alpha heating is comparable to or greater than the external heating source. Thus, the terms “dominant heating source” and “half the energy input” are used interchangeably throughout the text to indicate the required alpha-particle heating contribution for a burning plasma experiment.

3  

National Research Council, An Assessment of the Department of Energy’s Office of Fusion Energy Sciences Program, Fusion Science Assessment Committee (FUSAC), Washington, D.C.: National Academy Press, 2001 [hereafter referred to as NRC, FUSAC, An Assessment of the Department of Energy’s Office of Fusion Energy Sciences Program].



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