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PLASMA ASTROPHYSICS 125 nently frozen into the plasma and that the field never changes topology. Yet, magnetic fields apparently do change topology (e.g., the star formation process seems to reconnect the magnetic field), and there is strong evidence that magnetic reconnection is an important source of energy in solar flares. How do field lines reconnect at very high magnetic Reynolds number? Present thinking suggests a two-stage process: some ideal magnetohydrodynamic effect creates steep gradients; then reconnection proceeds. We need a more fundamental understanding of the reconnection process itself; many of the fusion-oriented simulations have inappropriate boundary conditions for astrophysical systems. We also need a better understanding of the "ideal" current concentration phase. The Magnetization of the Universe Stars, galaxies, and the gas in clusters of galaxies possess magnetic fields. Standard cosmology predicts that the big bang did not produce a magnetic field. How and when did the universe become magnetized? Did large-scale, intergalactic fields form first and become incorporated into smaller structures, or did fields form first in stars, which then seeded their ambient medium through winds and supernova explosions? Are astrophysical magnetic fields nearly permanent, as suggested by their very long ohmic decay times, or are they constantly destroyed, regenerated, and reconfigured by turbulent dynamos? Laboratory Experiments There have been few laboratory experiments dedicated to plasma astrophysics, and any such experiments must carefully scale properly from the laboratory to the real astrophysical system. Areas in which experiments could be helpful include MHD turbulence, magnetic reconnection, shock waves, particle acceleration, dusty plasmas, and heat conduction. The status and future promise of laboratory experiments in many of these and related areas are discussed in Chapter 8. TRAINING IN PLASMA ASTROPHYSICS How do graduate students become equipped to deal with problems in plasma astrophysics? The standard graduate curriculum in astrophysics contains graduate physics courses, such as quantum mechanics, electrodynamics, statistical mechanics, classical mechanicsâmore or fewer, depending on the school and the inclination of the student. Then there are standard astrophysics courses, such as stellar structure and evolution, stellar atmospheres and radiative transfer, interstellar medium, and galaxies and cosmology. At many universities, no courses in plasma physics are taught in the physics or astrophysics departments. Such courses may be given in an engineering or applied science department, but these
