Experimental and theoretical basis for advanced tokamaks

In this paper, arguments will be presented to support the attractiveness of advanced tokamaks as fusion reactors.The premise that all improved confinement regimes obtained to date were limited by magnetohydrodynamic stability will be established from experimental results.Accessing the advanced tokamak regime, therefore, requires means to overcome and enhance the beta limit.We will describe a number of ideas involving control of the plasma internal profiles, eg., , j, V4; P, to achieve this.These approaches will have to be compatible with the underlying mechanisms for confinement improvement, such as shear rot ation suppression of turbulence.For steady-state, there is a trade-off between full bootstrap current operation and the ability to control current profiles.The coupling between current drive and stability dictates the choice of sources and suggests an optimum for the bootstrap fraction.We summarize by presenting the future plans of the U.S.confinement devices, DIII-D, PBX-M, C-Mod, to address the advanced tokamak physics issues and provide a database for the design of next-generation experiments.