Symmetrized Magnetic Field Configuration of Low-Aspect-Ratio Helical System

Abstract

Helical magnetic field produced by the continuous helical windings has many multi-helicity (higher or satellite harmonics of a fundamental helical field) components. Generally these multi-helicity components enhance the ripple trapping and, as a result, increase neoclassical transport. A new method of a coil width modulation (a modulation of a helical coil current distribution) is proposed to reduce multi-helicity and to satisfy the requirement for the magnetic configuration of confining a high temperature plasma in a low-aspect-ratio helical system.