Engineering Design of a Flexible Heliac Device: The TJ-II Experiment

The flexible heliac TJ-II, is a medium size stellarator (R = 1.5 m; a =0.2 m), wiyh relatively low field (1T), a strongly helical magnetic axis and a high degree of flexibility that will allow to explore a wide range of magnetic configurations of the heliac type (rotational transform ranges from 0.9 to 2.5). It has obtained EURATOM preferential support and is now in construction. In this paper the main characteristics of the engineering design are discussed. The engineering has succeeded in maintaining all the physics objectives with very small sacrifices. It features a fully welded vacuum chamber that leaves all coils in the outside. High geometrical precision required in the chamber and ease of assembly are granted through modular construction in octants, which are the building blocks to be assembled together on site. All coils are made of directly cooled copper conductors. TF coils are made splittable in order to ease assembly of the machine. Accessibility to plasma is quite good through eighty eight ports of ample dimensions.