Design Scalings and Optimization for the Superconducting Large Helical Device

Abstract

This paper reports on optimization studies that have been carried out for the proposed Large Helical Device, which has a major radius of {approximately}4 m and a magnetic field of {approximately}4 T, in which a key experiment is to demonstrate a divertor concept. These studies clarified that configurations with a higher helical coil pitch parameter {gamma}{sub c} ({gamma}{sub c} {approx gt} 1.25) and a larger plasma minor radius are not consistent with the requirement of a clean divertor configuration. More compact, lower m systems (m {approx lt} 8) without helical coil pitch modulation are ruled out by the equilibrium beta limit of the plasma and the stability limit of the superconducting coil current because of the higher maximum magnetic field strength. Systems with a larger aspect ratio and larger m (M {approx gt} 12, {gamma}{sub c} {approximately} 1.2 to 1.3) with better neoclassical confinement properties are not effective because of a lower stability beta and a narrower clearance between the divertor layer and the wall. An 1 = 2/m = 10/{gamma}{sub c} = 1.2 superconducting system is found to be an optimized high-{eta}{sub {tau}}T configuration for 4 m/4T next-generation experiments with respect to the high-beta requirement, clean divertor installation, superconductingmore » coil engineering, and cost optimization.« less