Engineering aspects and present status of the Spanish stellarator TJ-II

TJ-II is a medium-size stellarator, (R₀ = 1.5 m; < a_p>=0.2 m; B_t=1 T) under construction at CIEMAT. It will allow the exploration of helical magnetic axis plasmas in a wide range af´ configurations (rotational transform ranges from 0.8 to 2.5, magnetic well up to 6%, and shear up to 10%) in discharges of 0.2 to 1 s, generated and heated by ECH (electron cyclotron heating) (400 kW at 53.2 GHz). <β> limits of the configuration, theoretically predicted to be as high as 6%, will be explored by the addition of 4 MW of NBI. The design criteria for this device and the solutions adopted for the different components are presented. Modular structure for the vacuum vessel, splittable toroidal field coils, and an independent support structure for each element, together with a detailed assembly procedure, allow independent and parallel construction of the different components. Strict requirements on tolerances, shapes, and current densities have been carefully addressed and solved in the design of the two most complicated components, the vacuum vessel and the central coils