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SPACE PLASMAS 118 the time scale of days or weeks, as contrasted with many years for satellites and several years for rockets. The hardware is reusable and flexible. Many different experiments can be performed on the same machine. The challenge to laboratory plasma science is to continue to develop technology in order to extend the range of physical phenomena that can be studied. It is now possible to fabricate microscopic detectors and antennae that are capable of making spatially resolved, in situ measurements of the electric and magnetic fields in the plasma, the electron and ion temperatures, the plasma potential, and the velocity distribution functions. Nonperturbing optical techniques, such as laser-induced fluorescence and optical tagging, are now well established. Other new techniques are time-resolved tomography, electron cyclotron emission spectroscopy, and the use of the motional Stark effect. Three-dimensional probe systems can move detectors (optical or electronic) anywhere within large devices, so that full space-time data sets can be acquired. Visualization software and three-dimensional-graphics computers make analyzing these data possible. Scientific areas in which laboratory simulation experiments can be carried out with current technology include properties of AlfvÃ©n waves, magnetic field line reconnection, wave-particle interactions leading to chaos, and current modulation of plasma conductivity. CONCLUSIONS AND RECOMMENDATIONS Space plasma physics, as the study of natural plasmas and associated technological applications, represents a vast multiscale physical domain with large variations in plasma sources, average thermal energy, flow velocities, magnetic field strength, and other underlying physical processes. As such, it represents an important regime for plasma science and technology and for our civilization. First, it provides us with an understanding in quantitative terms of the variety of interrelated complex processes acting to shape and influence our own terrestrial environment. Second, it affords the opportunity to observe at closer hand phenomena that may be operative in astrophysical situations. Third, space phenomena stimulate fundamental scientific questions relating to the behavior of plasmas under conditions that can be very different from those created and studied in terrestrial laboratories. And finally, space plasma science underlies the development of technological applications operating in or based on the space plasma environment. As a consequence, investigations of natural space plasma processes extend the frontiers of human knowledge, enabling broader physical understanding of plasmas within the context of their general behavior. Progress to date in understanding the space plasma environment has provided us with a broad picture along with some detail. However, many important details of physical mechanisms remain unanswered, including interdependencies between sources and physical responses. Successful investigation of this envi
SPACE PLASMAS 119 ronment requires a coordinated and balanced approach utilizing in situ observations, active experimentation, theoretical modeling, ground observations, and laboratory simulations. The requirement for a high degree of synergism is an inescapable conclusion. The cornerstones of space plasma physics are observations carried out, analyzed, and interpreted in conjunction with complementary theory and modeling. Space plasma physics has historically developed in this mode. With the advent of new technologies, opportunities for further scientific understandings are nearly limitless. In studies similar to this one, the space community is currently examining future directions and independently identifying possibilities. The panel supports such efforts. The use of space as a medium for active experimentation has declined to the point of near extinction. This is unfortunate, since active experiments may elucidate natural processes and expand in a unique way our basic understanding of the plasma state. The panel recommends a reinvigoration of the active experimentation area. Meaningful laboratory experiments simulating space phenomena can now be performed in a number of different problem areas. Such experiments provide the opportunity to examine the relevant science in a controllable and reproducible manner; they are thus an important adjunct to highly transitory space observations and can hence serve as a vehicle for interpreting, substantiating, and/or planning the latter. Such laboratory experiments have been largely discredited in the past because they did not scale properly to space conditions, but that shortcoming has been circumvented by developments in technology. The panel recommends an initiative in laboratory experiments of sufficient magnitude to establish a small interactive community.