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EXECUTIVE SUMMARY 22 the study of basic science relevant to inertial confinement fusion. Further, the panel recommends that the use of inertial confinement fusion facilities by scientists, working outside the program but on relevant problems, be encouraged. MAGNETIC CONFINEMENT FUSION Magnetic confinement fusion continues to be the largest driver for the intellectual development of plasma science. Central to the achievement of fusion in magnetically confined plasmas is the ability to confine hot plasmas (i.e., those with temperatures of more than 100 million Kelvin). Since these plasmas must eventually come in contact with material boundaries, this program also involves important considerations concerning low-temperature plasma science. Much progress has been made in this field over the past two decades. Confinement times of fusion plasmas have increased by a factor of more than 100, and achievable temperatures have increased by a factor of 10. Progress has been made in the development of new diagnostics of plasma behavior, and these diagnostics have, in turn, led to a deeper understanding of the behavior of fusion plasmas. New methods have been developed to heat fusion plasmas and to drive electrical currents in these plasmas noninductively using intense neutral beams and radio-frequency electromagnetic waves. These methods of current drive could eventually permit the operation of a steady-state fusion reactor. New operating regimes with improved plasma confinement have been discovered, such as the so-called "high-confinement" and "very-high- confinement" modes. There has been progress in the understanding of plasma stability as well as in understanding the interface between the plasma edge and the material walls of the confinement vessel. A key element in the magnetic confinement fusion program is the development of the International Thermonuclear Experimental Reactor (ITER). This device will be designed to test elements of reactor-relevant plasma science not possible by other means such as the physics of ignition. However, there are many other plasma processes relevant to controlled fusion that will not be able to be addressed effectively by the ITER program. The physics of the edge plasmas in tokamaks needs to be better understood. Advanced modes of tokamak operation at very long pulse lengths will be studied in the Tokamak Physics Experiment (TPX), now planned as a national facility for such studies. Finding improved methods of removing large quantities of heat from the plasma edge is an immediate problem. The efficient production of self-generated plasma currents by high plasma pressures (so-called "bootstrap currents") is an important goal of advanced tokamak configurations that is not likely to be studied efficiently in the ITER program. Experiment and theory should continue in the search for optimized geometries and operating conditions to improve reactor efficiency and power-handling capabilities.
EXECUTIVE SUMMARY 23 Crucial to the operation of a fusion device is the transport of particles and energy by plasma turbulence, and turbulent transport has been the dominant transport mechanism in all magnetically confined fusion plasmas to date. There is, as yet, only an extremely limited first-principles understanding of the turbulence in fusion plasmas and the resulting transport. Any predictive capability that does exist is based on empirical "scaling laws" that must be validated when applied outside the operating parameter range of present and past fusion devices. A quantitative understanding of this transport and the ability to control it could potentially lead to improved reactor performance and reduced size and cost. This fundamental base of plasma science is crucial not only for the efficient development of a successful fusion reactor, but also for quantitative understanding of fusion-related plasma science, which will continue to be important in maximizing the competitiveness of fusion power in the decades to follow. The panel recommends that there be established a coordinated research program in fusion-relevant plasma physics. This will require a range of project sizes, in order to optimize the particular experiments to study the relevant plasma processes. Experimental research is most efficiently done on the smallest scale possible. This allows the greatest flexibility in making changes, as required by new results and discoveries, as well as the greatest exploration of the relevant parameter ranges at minimum cost. Many fundamental questions in basic plasma science should be addressed by small experiments that, in many cases, are specifically designed for a particular purpose. Other questions can be addressed only in larger devices. To study the effects of fusion products (e.g., alpha particles at energies of a few million electron volts) on fusion plasmas, reactor-sized devices, such as the Tokamak Fusion Test Reactor or the Joint European Torus, are required. Thus, a coordinated program of fusion plasma research will require a range of devices and programs, from small, basic experiments that isolate and address fundamental questions in plasma science to experiments on the largest fusion devices. If the present trend toward large experiments continues without adequate attention paid to a broader base of experimental research facilities, a dangerous gap will develop in our ability to address the wide range of questions important to fusion-relevant plasma physics. Many important questions in fusion plasma physics might be more appropriately addressed by smaller, long-term research programs dedicated to isolating and studying fundamental plasma phenomena in a more complete and systematic manner. The panel recommends that the program in magnetic confinement fusion include support for a range of projects, with the sizes chosen to best suit the particular plasma problem. Provision needs to be made for research on fusion- relevant basic plasma science. The details of this recommendation are given below in Part II.