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SPACE PLASMAS 106 Laboratory Techniques Historically, laboratory experiments related to space phenomena never have been supported significantly by funding agencies, the exception being specific technology efforts such as electric propulsion. One reason is that it is costly and difficult to build experiments wherein the magnitudes of critical parameters scale with their space counterparts, a necessary condition for the laboratory work to be relevant. However, as a result of advances in general technology (i.e., developments in computers, digitizers, and other hardware), as well as large strides in the design and improvement of plasma devices, it is now possible to perform experiments that were not possible 15 years ago. This increased sophistication allows the possibility of meaningful laboratory simulations. Laboratory experiments can probe a process with unprecedented detail and uncover effects that may not be easily detectable in space. (See Plate 6.) Laboratory experiments can address both local and global physics issues, the latter often determined by boundaries. In some cases, one can comprehensively analyze physical phenomena simultaneously from both global and local points of view. Furthermore, experimental devices may be rapidly configured to perform new experiments as ideas are developed. This can happen on the time scale of days or weeks. The hardware is reusable and flexible. Many different experiments can be performed on the same machine. In addition to processes directly related to space plasmas, laboratory experiments have provided important technological advances within the areas of spacecraft propulsion and spacecraft potential control. Propulsion devices such as ion thrusters and arcjets, and plasma bridges, such as the plasma contactor, are being tested and studied in space with diagnostics developed largely for ambient plasma observations. FUNDAMENTAL PROCESSES IN SPACE PLASMAS Summarized below are a few basic phenomena of wide significance. Wave-Particle Interactions The important role of plasma waves in the macroscopic transfer of energy and momentum in space plasmas has become clear as a result of complementary and strongly coupled experimental and theoretical investigations. Over the last few decades, spacecraft observations have provided valuable information regarding the plasma environments around the Earth, planets, Sun, and comets. For example, from a limited set of planetary wave observations, it has become clear that similar waves exist around all the magnetized planets. This would seem to set limits on the significance of anthropogenic effects in triggering natural waves in Earth's magnetosphere. By far the largest body of information on the role of waves has been accumulated in Earth's plasma environment. Space
