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EXECUTIVE SUMMARY 26 ASTROPHYSICAL PLASMAS Plasma physics is relevant to almost every area of astrophysics, ranging from stellar and interstellar plasmas to star clusters and galaxies. The potential contribution of plasma physics to astrophysics has been limited by the fact that plasma physics is not yet part of the standard graduate astrophysics curriculum, and this should be changed. Also of concern to the panel is the fact that plasma astrophysics does not have a distinct home in any of the federal funding agencies. Examples of plasma astrophysics where there has been significant progress include models of magnetized accretion disks and associated jets and winds, including the effects of relativity, strong magnetic fields, rapid rotation, and magnetohydrodynamic waves and instabilities. Mechanisms of particle acceleration in plasma shockwaves have been clarified that are relevant to the acceleration of cosmic rays in the interstellar medium. Models have also been developed to describe the convective fluid motion in stars, including crucial effects arising from the presence of strong magnetic fields on the flow of stellar material. While there has been progress in plasma astrophysics, many fundamental problems need to be addressed. These include the description of dense stellar plasmas with temperatures in excess of 20 million Kelvin and densities 10 to 100 times solid density. Other important problems involve turbulent plasmas, the origin of the magnetic fields in the universe, and magnetic field line reconnection. Plasma astrophysics is not yet recognized as a coherent discipline by any federal funding agency. Yet, plasma astrophysics deals with phenomena that are important to virtually all aspects of astronomy and astrophysics, and many of these problems are central to basic plasma physics. The panel recommends that there be established interdisciplinary programs in the National Aeronautics and Space Administration and in the National Science Foundation to fund research in plasma astrophysics, including research on basic plasma processes relevant to astrophysical systems but not tied to any particular application. CENTRAL MESSAGES OF THIS REPORT The panel was charged with assessment of the state of plasma science in the United States and evaluation of its potential to contribute to the technology base of our society. It was further charged with assessing the institutional infrastructure in which plasma science is conducted, identifying changes that would improve the research and educational effort, and making recommendations to federal agencies and to the community to address these issues. The theme of this report is that, although plasmas are pervasive in nature and many of the applications of plasma science are being pursued and exploited effectively, plasma science is not adequately recognized as a discipline. Consequently,
EXECUTIVE SUMMARY 27 there is not an effective structure in place to develop the basic science that underlies its many applications. The potential contributions of plasma science to our society would benefit greatly by a coordinated effort of support for fundamental research, not tied to specific programs but designed to establish this basic scientific foundation. This report describes many of the developments in theory and experiment that have led to important industrial applications, significant commercial and residential uses, and a deeper understanding of the universe. While delineating the many successes and identifying the exciting and potentially critical challenges, this report is an expression of concern. Applications depend on development, which in turn depends upon a fundamental understanding of the underlying scienceâthe sine qua non of new development. It is the view of experts in the field that this fundamental understanding is, in most cases, best obtained by individual and small-group experimental and theoretical efforts, typical of university-scale programs. The problem is not that there is a gross imbalance in the total funding going into plasma science and technology, but that there has been a gradual, long-term decrease in support for fundamental research in plasma science. The result is that there is now a clear need for such support, particularly in the areas of small-scale, basic plasma experiments and complementary small-group theoretical efforts. As discussed above, a wide variety of programs pursue the applications of plasma science, including those in space, fusion, and the plasma processing of materials; yet there is great commonality of the underlying science. Even in the context of a particular application, there are often several programs, frequently spread across more than one federal agency. More often than not, this diversity is justified and healthy. However, coordination of research efforts is vital to eliminate duplication, to make the most effective use of resources by maintaining complementary programs, and to ensure that all of the critical problems are being addressed.4 A prime example of the existing lack of coordination in plasma research is the fact that no agency or agencies have yet assumed the responsibility for basic research in plasma science. Thus, the central messages of this report are threefold: 1. Small-scale research provides much of the fundamental base for plasma science; 2. Such individual-investigator and small-group research is in need of support; and 4 One beneficial effort of this type is the recent, informal coordination of experimental space plasma research by the National Aeronautics and Space Administration, the Office of Naval Research, and the National Science Foundation.
