Encouraging results with neutral-beam heating and adiabatic compression of tokamak plasmas have prompted new experiments which will study the approach to high-β states. As projected tokamak β-values become non-negligible (average β of 4% is the goal), the models previously used for transport calculations will become inadequate. The models will now be required to account for the evolution of the magnetic geometry, along with the change in plasma parameters. An axisymmetric-transport model is presented, which should be useful for studying the approach to higher β-values in tokamak experiments. Results from transport calculations with this model allow an analysis of the limits to β in two seemingly unrelated experiments: electron heating by neutral injection in the ORMAK device and adiabatic compression in the ATC experiment. By extrapolating empirical models for plasma transport, it is found that flux conserving (FCT) equilibria ought to be accessible by means of neutral beam heating. Finally, it is found that the nature of cross-field transport may be expected to change as significant β-values are reached. Enhanced transport from ballooning instabilities is likely to play a role as important as that now played by sawtooth (m = 1) and saturated (m = 2) instabilities. New techniques for describing this transport are required.
Free-expansion experiment on ATC