Modular Coils: A Promising Toroidal Coil System

The concept of modular coils originated from a need to find reactor-relevant stellarator windings. Considerations of 1) basic principles of modular coils, 2) types of coils, 3) types of configurations (general, helically symmetric, helically asymmetric, with magnetic well, with magnetic hill), 4) types of rotational transform profile, and 5) structure and origin of ripples are given. These results show that modular coils can offer a wide range of vacuum magnetic field configurations, some of which cannot be obtained with the classical stellarator or torsatron coil configuration.