Simulation of electromechanical and thermomechanical loads on first wall mock-ups

During the operation of a tokamak, the first wall elements suffer very high heat fluxes. Heat is removed by internal cooling by means of water, helium or fluid metal. The resulting inhomogeneous temperature field cause internal stresses which, due to the pulsed operation are of cyclic nature. Additional mechanical stresses in the first wall may be caused by disruptions or vertical plasma movements. During theses events high currents are induced in the metallic part of the first wall which by their interaction with the magnetic field of the tokamak lead to mechanical forces. These electromechanical stresses may lie beyond the yield stress of the structural material. From the interaction of thermal and mechanical forces, a complex stress state is achieved which under certain circumstances may lead to premature failure and/or to progressive plastic deformations (ratcheting). In order to study the boundary conditions for the occurrence of ratcheting, a testing rig has been erected at KFA. In this rig small scale mock-ups of first wall elements of 65 mm x 38 mm cross section and 800 mm length have been tested under mechanical conditions similar to those expected during disruptions. These mock-ups were made of stainless steel AISI 316