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the dominant instabilities driving turbulence has advanced to the point where the transport produced by this turbulence can be completely suppressed. Even a decade ago, the remote control of small-scale turbulence at the 100-million-degree cores of modern plasma fusion experiments would have been unthinkable. Yet significant inroads are now being made to surmount this critical hurdle of 40 years' standing. Theoretical predictions of fusion plasma behavior have led to the design, optimization, and testing of new plasma confinement approaches and new ways of controlling the macro- and microinstabilities that limit energy containment. The close interaction between theory and experiment represents the new face of the fusion energy sciences program.

A successful scientific enterprise develops state-of-the-art research tools, uses these tools to bring rigorous closure between experiment and theory, and then innovates. The ability to diagnose experiments on high-temperature plasmas and compare the results with theoretical models and numerical simulations has improved markedly over the past two decades and in the committee's view is itself an important achievement of the field of fusion science. The enhanced ability to bring to closure some of the complex problems facing the discipline presages a new period of scientific development and supports a science-based strategy for fusion energy.

Another measure of the quality of a scientific program is the international standing of the discipline supported by the program. The U.S. fusion program has traditionally been an important source of innovation and discovery. A distinguishing feature of the program has been its goal of understanding at a fundamental level the physical processes governing observed plasma behavior. This feature, a strength of the program, was formalized in the 1996 restructuring with the new emphasis on establishing the knowledge base for fusion energy. Over the past several decades, the United States has played a dominant role in plasma theory, which is an essential tool required to unravel the complexities of plasma dynamics. The quantitative detail in which experiments are designed and executed in this country has become a benchmark for the rest of the world. The forte of the U.S. program is, as was mentioned above, the close confrontation between theory and experiment and the development of superior computational physics codes for quantitative exploration of novel physical concepts.

To assess the specific contributions of the DOE's OFES program to the fusion effort in general, one must separate the U.S. effort from the broader international effort. This is not easy, because there has been close interaction between the U.S. and international programs since the beginning, in the 1950s. To be specific, U.S. scientists played a major role internationally in developing the energy principle for describing plasma stability; heating and sustaining currents in plasmas; and understanding and controlling plasma turbulence and transport. (Specific examples of U.S. and foreign contributions can be found throughout the discussion in Chapter 2 and in Chapter 4, in the section devoted to U.S. contributions.)

In short, the quality of the science that has been deployed in pursuit of the fusion energy goal is easily on a par with other leading areas of contemporary physical science. Fusion research has mastered the ability to work flexibly with the super-high-temperature plasma state in the laboratory. It is important to note that the quality of fusion science is not universally appreciated within the broader scientific community, perhaps because fusion has been viewed as a directed energy development project rather than as a scientific enterprise. Isolation of the researchers inside the fusion program from those outside the program is another possible cause for the low opinion of fusion science despite its high quality. Most scientists funded by the program do not actively participate in the wider scientific culture. As a result, the flow of scientific information both out of and into the field has weakened. New ideas and techniques developed in allied fields are slow to percolate into the program.

All in all, a half century of research suggests that the central scientific barriers to the achievement of fusion energy will ultimately be overcome, although it is still not possible to predict when sustained fusion energy production will be realized, and much scientific and engineering work remains to be done.

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