BACKGROUND

Fusion is the process by which energy is produced in the sun, and, on a more human scale, is the one of the key processes involved in the detonation of a thermonuclear bomb. If this process could be “tamed” to provide a controllable source of energy that can be converted to electricity—as nuclear fission has been in currently operating nuclear reactors—it is possible that nuclear fusion could provide a new method for producing low-carbon electricity to meet U.S. and world growing energy needs.

For inertial fusion to occur in a laboratory, fuel material (typically deuterium and tritium) must be confined for an adequate length of time at an appropriate density and temperature to overcome the Coulomb repulsion of the nuclei and allow them to fuse. In inertial confinement fusion (ICF)—the concept investigated in this report2—a driver (e.g., a laser, particle beam, or pulsed magnetic field) delivers energy to the fuel target, heating and compressing it to the conditions required for ignition. Most ICF concepts compress a small amount of fuel directly to thermonuclear burn conditions (a hot spot) and propagate the burn via alpha particle deposition through adjacent high-density fuel regions, thereby generating a significant energy output.

There are two major concepts for inertial confinement fusion target design: direct-drive targets, in which the driver energy strikes directly on the fuel capsule, and indirect-drive targets, in which the driver energy first strikes the inside surface of a hollow chamber (a hohlraum) surrounding the fuel capsule, producing energetic X-rays that compress the fuel capsule. Conventional direct and indirect drive share many key physics issues (e.g., energy coupling, the need for driver uniformity, and hydrodynamic instabilities); however, there are also issues that are unique to each concept.

The only facility in the world that was designed to conduct ICF experiments that address the ignition scale is the NIF at LLNL. The NIF driver is a solid-state laser. For the first ignition experiments, the NIF team has chosen indirect-drive targets. The NIF can also be configured for direct drive. In addition, important work on laser-driven, direct-drive targets (albeit at less than ignition scale) is also under way in the United States at the Naval Research Laboratory and the OMEGA laser at the University of Rochester. Heavy-ion-beam drivers are being investigated at the Lawrence Berkeley National Laboratory (LBNL), LLNL, and the Princeton Plasma Physics Laboratory (PPPL), and magnetic implosion techniques are being explored on the Z machine at Sandia National Laboratories (SNL) and at Los

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2 Inertial confinement fusion (ICF) is the process by which the target is heated and compressed by the driver to reach fusion conditions. Inertial fusion energy (IFE) is the process by which useful energy is extracted from ignition and burn of ICF fuel targets.



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