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EXECUTIVE SUMMARY 11 phenomena as sunspots, the formation of stars from interstellar gas clouds, the acceleration of cosmic rays, the formation and dynamics of energetic jets and winds from stars and galaxies, or the interaction of supernova remnants with interstellar gas, without the concepts of plasma science. Plasmas are central to many aspects of space science. The space plasma medium extends from the ionosphere surrounding the Earth to the far reaches of the solar system. "Space-weather" prediction in the ionosphere and magnetosphere is important for global communications, and the properties of space plasmas are important in determining the capabilities and longevity of spacecraft. Thus, although it is often not readily apparent, plasma science affects our society in a myriad of ways. THE DISCIPLINE OF PLASMA SCIENCE COMMON RESEARCH THEMES The panel has concluded that plasma science is frequently viewed, not as a distinct discipline, but as an interdisciplinary enterprise focused on a large collection of applications. The underlying, common, and critical feature of plasma science as a discipline is that its goal is to understand the behavior of ionized gases, and this requires fundamentally different techniques from those applicable to uncharged gases, fluids, and solids. This coherence of plasma science as a discipline is apparent when one considers some of the challenging intellectual problems, central to plasma science, that span applications in many of the topical areas. The impact of four such problems on the topical areas assessed in this report are summarized in Table S.1. Wave-Particle Interactions and Plasma Heating Understanding the interaction of plasma particles with the collective plasma oscillations and waves is a fundamental question with many practical applications. Basic scientific issues involve the trapping of particles in waves, the nonlinear saturation of wave damping, chaotic behavior induced in particle orbits, and particle acceleration mechanisms. Wave heating is an important method of heating fusion plasmas to the required temperatures for fusion. Waves can be used to drive electrical currents in plasmas. One promising scheme for a steady-state tokamak fusion reactor is to use waves to drive electrical currents to confine the plasma, instead of the present method of driving pulsed currents inductively. Wave-particle interactions are central to the operation of free-electron lasers and other coherent radiation sources, to many advanced accelerator concepts, and to methods of creating and heating low- temperature plasmas for plasma processing applications. Wave-particle processes are important in Earth's magnetosphere and ionosphere, and shock waves are the dominant production mechanism for cosmic rays of astrophysical origin.
TABLE S.1 Applications of Basic Plasma Research, Illustrating the Commonality of Scientific Issues Across Topical Areas Scientific Issue Topical Area Wave-Particle Interactions Chaos, Turbulence, and Sheaths and Boundary Magnetic Reconnection and and Plasma Heating Transport Layers Dynamos Low-temperature plasmas Magnetrons Instabilities in plasma Plasma processing Plasma torches Plasma sprays processing Lighting MHD drag reduction Nonneutral plasmas ICR mass spectrometry Precision clocks Switches â EXECUTIVE SUMMARY Fluid flows Diodes Antimatter storage Inertial confinement fusion Parametric instabilities Turbulent mixing Plasma-driver interface ICF plasma magnetic fields Preheating Rayleigh-Taylor instability Magnetic confinement rf current drive Energy and particle loss Divertor operation Sawteeth and current profile fusion rf plasma heating Plasma-limiter interaction dynamics in tokamaks Reversed-field pinches 12
Beams, accelerators, and FELs Instabilities in FELs and Cathodes â coherent radiation sources Advanced accelerators advanced accelerators Space plasmas Magnetosphere Cometary and planetary Magnetospheric and Solar interior and corona Ionosphere atmospheres ionospheric boundaries Magnetopause Solar wind plasma-satellite interaction Astrophysical plasmas Cosmic-ray acceleration Accretion disks Pulsar magnetospheres Solar and stellar magnetic Dynamo viscosity Accretion disk boundaries fields EXECUTIVE SUMMARY NOTE: ICR = ion cyclotron resonance rf = radio-frequency FEL = free-electron laser MHD = magnetohydrodynamic ICF = inertial confinement fusion 13