Optimization of energy confinement in the 1/ν regime for stellarators

A set of powerful tools has been developed in the last years for the design of new stellarator devices. These codes, usually working in magnetic co-ordinates, comprise minimization of neoclassical transport, maximizing equilibrium and stability properties, etc. However, for certain conditions the stellarator magnetic field can be originally obtained in the real space coordinates and there is no necessity in its transformation to magnetic coordinates. Here a procedure working in real space co-ordinates is presented for maximizing the plasma energy content, based on reducing the most unfavorable, 1/nu, neoclassical transport. This tool is especially useful for existing stellarator devices which are not fully optimized with respect to neoclassical transport. Preliminary results for the "heliac-type" stellarator TJ-II are presented showing a configuration with almost twice the stored energy of the standard TJ-II configuration. (c) 2008 Elsevier Inc. All rights reserved.