ITER physics design guidelines, at high aspect ratio

The physics requirements for ITER (International Thermonuclear Experimental Reactor) design are formulated in a set of physics design guidelines. These guidelines were based on credible extrapolations of the tokamak physics database as assessed during the conceptual design activity (CDA) and defined a class of tokamak designs (with plasma current I~20 MA and aspect ratio A~2.5-3.5) that meet the ITER objectives. Recent studies have indicated that there may be significant benefits in moving the ITER-CDA design point from the low-aspect-ratio, high-current baseline to a high-aspect-ratio machine, especially in terms of steady-state, technology-testing performance. To adequately assess the physics and technology testing capability of higher-aspect-ratio design options, several changes are proposed to the original ITER guidelines to reflect the latest (although limited) developments in physics understanding at higher aspect ratios. The critical issues for higher-aspect-ratio design options are listed and discussed