Use of nonaxisymmetric shaping in magnetic fusion

Abstract

Nonaxisymmetric shaping of magnetic fusion plasmas extends the design space of nominally axisymmetric configurations, such as the tokamak, and defines fundamentally nonaxisymmetric configurations, called stellarators. Shaping is the primary design freedom to ensure suitable plasma equilibria for fusion applications. In fusion plasmas, the plasma pressure and current distributions are largely self-determined, and the only other determinant of plasma equilibria is the plasma shape. Since most of the freedom of shaping is in nonaxisymmetric shaping, understanding is needed. No fundamental demarcation exists between axisymmetric and quasiaxisymmetric tokamaks, so nonaxisymmetric shaping can be used to address issues that must be addressed for tokamaks to be an attractive fusion system. Stellarators offer design freedom beyond that available from extending the design space of nominally axisymmetric concepts. Stellarator experiments have demonstrated many benefits of nonaxisymmetric shaping, but the primary benefit is that sufficient freedom exists to design around many problems of fusion plasmas.