The International Thermonuclear Experimental Reactor (ITER) tokamak superconducting magnet system is designed to confine and control a 21 MA plasma during the various phases of pulsed operation. The central solenoid (CS) and poloidal coils are independently powered with currents that cycle during the pulse. The reference magnet system design includes a layer-wound 12 meter long CS that only allows one current density distribution. In an alternative design, which shows advantages for plasma shape control, the CS consists of three independently powered modules. The central module is a layer-wound coil, as in the reference design, but shorter (9.5 m). The neighboring modules are pancake-wound free standing coils and are located above and below the central module. In both configurations the toroidal field (TF) and CS coils are linked since the centering forces of the TF coils are reacted onto the central portion of the CS. For both configurations, the CS requires vertical precompression to suppress the tensile vertical stress at the joint area due to the CS bending, arising from the variation of TF pressure over the height of the CS. The segmented configuration requires a higher CS preload at room temperature to suppress vertical tension in the joint area.

In this paper the configurations are compared from the structural point of view. To investigate the global behavior of the magnet system with different CS configurations 2D and 3D finite element (FE) global models have been developed. Preloading of the CS at room temperature, cooldown, TF on and electro-magnetic loads during a poloidal field pulse are included in the loading history.

A set of 2D FE models of the joint areas have been built as well to define the required vertical preload of the CS. Results concerning both the global stress variation in the magnet system with time and local stress distribution at the joints area are presented. The electro-magnetic load limits have been calculated to be within the allowable hoop stress for the free standing coils in the CS segmented configuration. Analysis shows the reference design to be preferable from the point of view of the stress levels. Due to the increased TF coil out-of-plane bending, the design with the CS segmented configuration shows an insulation bonding shear requirement about 25% above the reference design and an increased TF bending stress which gives a predicted lifetime of the TF coil case of about 60% of the reference configuration.