Alternative concepts: Physics advances and prospects

Research in a diverse range of confinement concepts permits study of fusion plasma physics in ways not possible in only one concept; ultimately, a fusion reactor will likely draw on attributes from many configurations (to which we presently apply distinct labels which understate their physics connections). For example, the field reversed configuration, reversed field pinch, spherical tokamak, spheromak, stellarator, dense z-pinch and electrostatic Penning trap combine to offer a range of concepts with varying magnetic shear, curvature, fluctuation levels and spectra, plasma flow, density and temperature gradients, plasma currents and boundary conditions. Resulting from this diversity, a wide range of new phenomena and ideas has been uncovered in recent years involving confinement with safety factor q < 1, currentless two dimensional systems, dynamo phenomena, large orbit effects on stability, magnetic fluctuation driven transport, physics at extreme toroidicity, plasma relaxation, helicity injection, plasma flow and mode locking, and particle focusing, to name a few. In addition, many of these alternative concepts (by which we mean anything other than the medium-aspect-ratio advanced tokamak) arguably have potential advantages as a fusion reactor. Many are aimed at a smaller, simpler, higher beta reactor with lower magnetic field. This talk will focus on selected recent physics advances (experimental and theoretical) arising within alternative concepts research. We will also discuss the reactor potential of the concepts, particularly key physics obstacles (or challenges)