An important contribution to the mechanical stresses present in the ITER ICH antenna is related to the non-uniform heating of its front section due to RF losses, plasma and charge exchange, and the effects of neutron radiation. As a consequence, intensive convective cooling is necessary to maintain temperature and the related thermally induced stresses below their permissible levels.
Design effort had been focused on thermal design development of the ITER ICH antenna straps with the main objective to maximise cooling performance of their internal water channels. In the initial stage, a set of strap design variations was analysed using a representative 2D strap section to quantify thermal resistances associated with strap design elements, improve conductive heat transfer between load surfaces and coolant flow, enhance convective cooling, reduce mechanical stress in the straps, and to propose a strap design solution for a 3D thermo-structural analysis. As a result, the number of cooling channels was increased, and their diameter reduced. Although, reducing the strap thickness may also improve its thermal performance, disruption induced mechanical loading prohibits such a design solution. Different material combinations were evaluated to provide an acceptable compromise between the strap thermal performance, stiffness and allowable stress limits. Copper was removed from the design to reduce the electro-magnetic forces induced during disruptions and stainless steel 316L(N) was replaced with Inconel 625 to raise the allowable stress limits especially at elevated temperatures.