Structural analysis of the ITER upper port mounted bolometer camera

Abstract

The ITER bolometer diagnostic provides the absolutely calibrated radiation emitted by the plasma, which is a part of the total energy balance. The development of its components is especially challenging because of the extreme environmental conditions within the vacuum vessel during plasma operation. Reliable measurements have to be assured while being subjected to high neutron fluxes as well as plasma radiation resulting in temperatures of the components exceeding 200°C. In addition to the thermal loads, the bolometer camera housing is exposed to mechanical loads caused by electromagnetic forces (EM) during transient events of the plasma operation, called disruptions.Bolometer cameras are positioned all over the plasma vacuum vessel. This paper describes the structural analysis of a camera located in the upper port plug. To examine all important structural responses of the camera body, an elastic nonlinear finite element model has been employed, considering the loads from the assembly and the operation. The design assessment follows the ITER criteria and the RCC-MR code.The analysis validates the camera design and addresses the critical loads, then optimization plans are proposed. Two important design changes are introduced in this paper, one is the mounting connection of the camera, which has to sustain EM forces in the range of 100kN. A wedge-type shear key design is applied, to reduce the problematic shear force on the mounting bolts due to the EM loads. Pre-stressing the shear keys allows accommodating the thermal expansion difference between the camera housing and the port plug structure. The other design improvement is the camera housing optimization, in order to reduce the bending deformation under the EM force and to reduce stress concentrations. All the design improvements have been confirmed by analyses and further design evolutions are ongoing.