Optimization of Compact Stellarator Configuration as Fusion Devices

Optimization of the stellarator configuration requires trade-offs among a large number of physics parameters and engineering constraints. An integrated study of compact stellarator power plants, ARIES-CS, aims at examining these trade-offs and defining key R{\&}D areas. We developed configurations with A$\le$6 and excellent QA (both 2 and 3 field periods) while reducing $\alpha$ losses to $\sim $10{\%} (still higher than desirable). Stability to the linear ideal MHD modes was attained but at the expense of reduced QA (and increased $\alpha$ losses) and increased complexity of the plasma shape. Recent experimental results indicate, however, linear MHD stability limits may not be applicable to stellarators. It appears that the plasma/coil stand-off distance is not as an important as envisioned previously. By utilizing a highly efficient shield-only region in strategic areas, we reduced the minimum stand-off by $\sim $20{\%}-30{\%}. This allows a comparable reduction in the machine size. The device configuration, assembly, and maintenance procedures appear to impose severe constraints. A cost-optimization system code has been developed and is utilized to guide the optimization process.