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NONNEUTRAL PLASMAS 56 that is expected for a large-volume plasma remains to be studied experimentally. Such experiments will test the predictions of recent theories. Furthermore, for modest-sized plasmas, the theoretical prediction of ordering in concentric spheroidal shells is at variance with observations of open cylindrical shells. This significant discrepancy also remains to be reconciled. Although there is now a good understanding of many features of the equilibria of ion plasmas and of the linear dynamics of these plasmas about their equilibria, many important questions remain. For example, the transport coefficients (such as the viscosity and the thermal relaxation time) in strongly correlated, magnetized, nonneutral plasma are not understood theoretically. Experiments can measure many of these coefficients. It is likely that future interplay between theory and experiment in this area will be productive in elucidating these fundamental transport processes. Quantum-Mechanical Effects The tools now exist to create plasmas in correlated spin states and to create quantized plasmas, in which the quantum-mechanical ground state energy is large compared to the thermal energy in a plasma mode. Another important area for future study relates to the properties of nonneutral plasmas at or near the Brillouin density limit. Antimatter The efficient trapping of single-species plasmas has been exploited for the confinement and cooling of both antiprotons and positrons. Further progress in developing efficient techniques for the confinement and manipulation of single- species plasmas will directly benefit studies of antimatter and the interaction of antimatter with ordinary matter. Improvements in the trapping and manipulation of single-component plasmas will lead to the ability to transport antimatter (such as antiprotons) from high-energy accelerators, where they are created, to laboratories throughout the world. Many important scientific questions can be addressed by collections of antimatter particles confined in traps. For example, one can study the physics of electron-positron plasmas. These plasmas are unusual in the sense that both signs of charge can be highly magnetized, and the "electron-ion" mass ratio is unity. Important physics issues include the nature of confinement and transport in these neutral but highly magnetized plasmas and the nature of fluctuations and turbulence in such equal-mass plasmas. The interaction of low-energy positrons with ordinary matter can also be studied with precision in traps, to address questions relevant to atomic and molecular physics and to gamma-ray astronomy. The 511-keV gamma-ray annihilation line is the strongest astrophysical source of gamma-ray line radiation. Trapped antiprotons will be of use for fundamental
