Analysis of Stress Induced by Plasma Disruption on Vacuum Vessel through Multi-physics Modeling.

The analysis of the stresses induced on the vacuum vessel (VV) of a Tokamak and its internal components by the plasma instabilities, such as plasma disruptions, also following a Vertical Displacement Event (VDE) is one of the major concern in the Tokamak design. So the availability of a fast simulation tool for evaluating different design options, also able to perform parametric analysis, is highly attractive to define the project requirements and to verify the conceptual design. To respond to this wish, a methodology based on the multi-physics modeling capability offered by the Comsol® software platform was developed. It consists in coupled simulations based on the data sharing between two 2D axisymmetric model, everyone coupled with a corresponding 3D model, shifted each other of 10 degrees. In the 2D axisymmetric model of every couple, the magnetic and electric fields generated by the plasma VDE and disruption, are calculated imposing the plasma time evolution as input. In the corresponding 3D model only the mechanical structures are present and on them the Electric and Magnetic fields are extruded, determining so the induced currents diffusion in the passive conductors. Then the resulting Lorentz's forces are imposed as body loads on the mechanical structures, so a linear stress analysis can be carried out after the constraints assignment. The same procedure is followed with the second couple of 2D/3D models for check purposes, comparing some proper physical quantities, such as the total induced current flowing on the VV. In this paper the methodology is presented by reporting the simulation of a double null plasma VDE, lasting c.a. 100 ms, followed by a full 5.5 MA plasma current quench in about 40 ms.