Optimization of compact stellarator configuration as fusion devices

Abstract

Optimization of the stellarator configuration requires tradeoffs among a large number of physics parameters and engineering constraints. An integrated study of compact stellarator power plants, ARIES-CS, aims at examining these tradeoffs and defining key R&D areas. Configurations with a plasma aspect ratio of A⩽6 and excellent quasiaxisymmetry (QA) in both two and three field period versions were developed while reducing α-particle losses to <10%. Stability to linear ideal MHD modes was attained, but at the expense of reduced QA (and increased α-particle losses) and increased complexity of the plasma shape. Recent experimental results indicate, however, that linear MHD stability limits may not be applicable to stellarators. By utilizing a highly efficient shield-only region in strategic areas, the minimum standoff was reduced by ∼30%. This allows a comparable reduction in the machine size. The device configuration, assembly, and maintenance procedures appear to impose severe constraints: three distinct approaches were developed, each applicable to a certain blanket concept and/or stellarator configuration. Modular coils are designed to examine the geometric complexity and to understand the constraints imposed by the maximum allowable field, desirable coil-plasma separation, coil-coil spacing, and other coil parameters. A cost-optimization system code has also been developed and will be utilized to assess the tradeoff among physics and engineering constraints in a self-consistent manner in the final phase of the ARIES-CS study.