Plan of vibration tests for estimation of seismic performance of ITER tokamak

The ITER tokamak is composed of major components such as superconducting magnet and vacuum vessel whose operation temperatures are changed from room temperature to 4 K and room temperature to 200 degC, respectively. The gravity support structure of the tokamak is flexible in order to accept the thermal deformation caused by temperature change. It is expected that this structural feature causes the complex behaviors of the tokamak during seismic events. The seismic design of the tokamak has to therefore be considered to ensure the integrity. For this, the numerical analysis model for estimation has to be verified by the experiments because there is few report on the dynamic analysis of this kind of flexible structure in the past. In particular, the gravity support is a complicated structure composed of flexible plates and connection bolts. Therefore, the effect on the mechanical characteristics of the flexible support structure has to be investigated in detail during vibration. The present report describes the global plan of the series of vibration tests to estimate the seismic performance of the ITER tokamak. Although it is ideal that the vibration tests are carried out using a full-scale model, scale models are planned due to the limitation of the test facilities. The test results can be estimated by a scaling law. When the scaling law cannot be applied to some performances such as damping, the test is performed using a full-scale model. In addition, the other complimentary tests using a scale model such as vacuum vessel and small-scale models of support structure are also planned. Details of the global plan on vibration tests are shown in this report as follows. (1) Tests for which the scaling law is applicable: Scale model test of the whole tokamak: investigation of horizontal vibration mode affecting on displacement and validation of analysis model. Scale model test of vacuum vessel: investigation of deformation modes of the vacuum vessel structure, the effect on vibration characteristics of whole tokamak and validation of analysis model. Small-scale model test of support structure: investigation of detailed vibration characteristics of the support structure. (2) Tests for which the scaling law is not applicable: Full-scale test of support structure: investigation of some characteristics such as damping, whose scaling is not applied. Furthermore, an effect of the support structure on horizontal vibration mode is estimated with the numerical analysis. As a result, it is found that the support structure and the internal deformation of components combinedly affect on the vibration characteristics of the whole structure. (author)