Confinement study of net-current free toroidal plasmas based on the extended international stellarator database

Full text: A global database in stellarators has been updated by incorporating new experiments as part of an international collaboration. The present study examines the expanded database involving data from 9 devices for confirmation and examination of new trends in confinement performance of stellarators. A simple regression analysis with the set of parameters of major and minor radii, magnetic field, density, heating power and rotational transform is useful for unified data description but its application is limited to the available data set alone. Acceptance of a systematic difference in different magnetic configurations is a prerequisite for derivation of a useful unified scaling law. A deterministic parameter characterizing the magnetic configuration has not been clarified yet, but certainly involves the details of the helically corrugated magnetic fields, so an enhancement factor on the ISS95 scaling is used for description of the magnetic configuration effect. This renormalization of data results in a scaling expression with gyro-Bohm nature and no clear dependence on beta and collisionality. The underlying physics of the enhancement factor and potential for reactor assessment are discussed. (author)