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BASIC PLASMA EXPERIMENTS 144 RESEARCH OPPORTUNITIES Fundamental Plasma Processes The following is a selection of important fundamental problems in basic plasma science that could be addressed in the next decade by a new generation of plasma experiments. Wave Phenomena Alfvén Waves. Alfvén waves are modes of oscillation of a magnetized plasma at frequencies below the ion cyclotron frequency. They are important both in fusion plasmas and in space plasmas, such as the solar wind and the Earth's magnetosphere and ionosphere. Alfvén waves can act to transport information about magnetic field disturbances in magnetized plasmas. Alfvén waves and their high-frequency analogue, magnetosonic waves, are important in magnetic confinement fusion research, where they are candidates for plasma heating and noninductive current drive. In spite of their importance, relatively little work on these waves has been done in the laboratory because Alfvén waves have relatively long wavelengths (1â5 m) in plasmas of reasonable density. Recently, well-diagnosed plasmas have been developed that are sufficiently dense and large enough to accommodate several Alfvén wavelengths. Thus, carefully controlled laboratory Alfvén wave experiments are now possible. Topics currently under investigation include the dispersion relation for these waves, their reflection properties and spatial structure, and the nonlinear behavior of these modes. Wave-Plasma Interactions. Wave-plasma interactions have been under active investigation, but many important questions remain. Outstanding issues include the modulation of plasma currents by waves and the modulation of low-frequency waves (e.g., Alfvén and whistler waves) by local fluctuations in the plasma conductivity. Another important problem that has not yet been studied experimentally is resonant absorption in the situation where a wave propagates along a density gradient that is parallel to the magnetic field. Important effects include nonlinear refraction and the generation of non-Maxwellian electron distribution functions and Langmuir turbulence. Such experiments are relevant to fusion physics as well as to heating of the F-region of the ionosphere. Information generated by these experiments also may be relevant to the development of advanced particle accelerators and to the generation of intense electromagnetic waves. Intense Laser-Plasma Interactions. As described in Chapter 5 on beams and radiation sources in Part II, recent technological developments have led to the
