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The Fusion Reaction

How an environmentally friendly power source can solve the fossil-fuel supply-and-demand gap.

Fortnightly Magazine - August 2005
Figure 4 - Configuration Comparison

the project, full blanket development will require additional facilities. For example, sufficient irradiation testing volumes and neutron fluence (neutron flux times irradiation time) will be needed for blanket materials development.

The most economical approach to materials testing would be to employ a deuteron accelerator to irradiate a lithium target, producing a high flux of neutrons within a modest testing volume. This test volume would be sufficient for materials tests, but not adequate for blanket systems tests.

Further Tests

For the demo to meet its ambitious goals, additional technology development will be required beyond that of ITER. A much smaller device, the Component Test Facility (CTF), will provide the technology development bridge between ITER and the demo. CTF would use a driven deuterium-tritium plasma with low-fusion output, enabling blanket materials development in a relevant fusion environment on the smallest possible scale. While the fusion power output will be modest, the flux and fluence will be relatively high because of the modest size of the device. This is a faster, much less expensive, less risky approach than testing in a large device that would be limited by tritium consumption, and which would have a very large blanket needing replacement for multiple tests. If necessary, more than one CTF could be constructed.

Figure 5 - International Thermonuclear Experimental Reactor

ITER will have about 20 percent of the power rating required by a commercial power reactor of similar size. In addition, the ITER plasma will not be sustainable for steady state operation. The present research program in the United States is directed toward providing the physics and technology base to bridge the performance gap among ITER, CTF, and the demo, along with broadening the configuration options available for these devices. The United States is carrying out programs to strengthen the physics base. The magnetic confinement approach is being pursued by the General Atomics Corp., Oak Ridge National Laboratory, MIT, PPPL, and a number of other laboratories nationally and worldwide. The U.S. Department of Energy's Office of Science funds fusion research in the United States.

PPPL is constructing and testing potential configuration improvements. One of these, the National Spherical Torus Experiment (NSTX) at Princeton, 5 is a compact variant of the well developed Tokamak, with the potential for use as a CTF. The configurational feature that facilitates reduction in size is a plasma envelope patterned after a fat donut with a very small hole in the center. The need for a very small space in the center of the reacting chamber facilitates a compact overall configuration. A second configurational improvement being developed at Princeton is the compact stellarator. 6 A comparison between a conventional configuration, a spherical torus, and a stellarator is shown in Figure 4. The stellarator uses three dimensional shaping to facilitate steady state operation.

Fusion energy research has brought a level of development that supports the construction and operation of the ITER. A plan is in place for the remaining development required to construct a demonstration fusion power plant. The plan leads to significant fusion power production after mid-century, filling the widening energy supply/demand gap during this period and for the

Figure 6 - Fusion Power Plant Schematic