High heat fluxes and high electromagnetic loads make for a challenging combination in the design of the ITER divertor cassette and plasma facing component (PFC) attachments. The cassette body must be able to handle high bending moments imposed by the electromagnetic (EM) forces in areas with cross sections that are reduced due to coolant channel, vacuum port, gas box, shoe and PFC cut-outs. The ITER divertor cassette design incorporates removable, high heat flux components (PFCs) whose lives are shorter than the cassette body due to the more severe loading conditions. The PFC attachments must be designed to withstand the high EM and thermal loads and have limited constraint in order to minimize thermal stresses.

The electromagnetic loads on the divertor cassette result in typical forces on the PFC's in the order of 1 MN and bending moments on the body of 1 MN-m. The forces used in the structural design correspond to general halo currents as well as a Vertical Displacement Event (VDE) followed by a 100 ms current quench. In addition thermal loads must also be considered in the design. Surface heat fluxes range from a nominal of 5 MW/m² to a peak of 20 MW/m² and are incident on the PFC surfaces. Volumetric heating also occurs, peaking at 10 W/cm³ in the PFCs and 0.5 W/cm³ in the body. These surface heat fluxes and volumetric heating result in differential thermal growth between the PFC's and cassette body which must be accommodated. The attachment concepts must themselves be maintained within allowable temperatures, which limits their size and requires a certain proximity to the coolant. Volumetric heat removal requires a complex matrix of coolant channels to control local temperature. These must be placed so that the structural integrity of the cassette is not compromised.

The cassette body and PFC attachments must be designed to withstand these environments. General body configurations and local cross sections, including cooling channel details, have been examined for the above loading conditions. A variety of attachment concepts have also been examined for the different PFC locations and conditions. Dumbbell, keyhole, L-shaped, T-shaped, and mushroom-shaped attachments have been considered as well as lugs with a mandrel-deformed hollow pin.

* Work supported by US DOE under Contract AC-3013 with Sandia National Laboratories.