A Multiphysics Ray Optics Model for the Propagation of Electromagnetic Waves in Plasmas and the Design of Laser-Based Diagnostics in Nuclear Fusion Reactors

Laser-based methods are widely used techniques for thermonuclear plasma diagnostics, since they can probe the internal of the plasma, being contactless and non-invasive. The interferometer, the polarimeter and Thomson scattering are the most widespread techniques, providing line-integral information of the electron density and the magnetic field (interferometer–polarimeter) and local information of the electron density and temperature (Thomson scattering). The design of the diagnostics is a fundamental step, which usually requires an iterative process to maximise the performances of the diagnostics and their durability. In the future reactors, such as ITER and DEMO, the working environment will be much challenging, due to the various electro-mechanical, thermal and nuclear loads which may affect the life of the components and degrade the performances of the diagnostics. This work aims to present the modelling of plasma interferometry, polarimetry and Thomson scattering applied to a ray optics code. The model, developed on the COMSOL Multiphysics software, can be easily interfaced with multiphysics problems, allowing the possibility to test the performances of the diagnostics in several conditions.