Monte Carlo and Molecular Dynamics Simulations of Plasma-Material Interactions

The design of a suitable interface between plasma heated at millions of kelvin and the environment is one of the most critical areas within nuclear fusion research. The surface of interface components should sustain the energy delivered by plasma as electromagnetic radiation and transported through charge carriers such as ions and electrons. The ratio between available plasma energy and heated surface increases with device dimension, so that for ITER and future fusion reactors the energy density striking the tokamak walls will be order of magnitude higher compared to what happens in current facilities. Several plasma material interaction phenomena are relevant for PFCs design. The high energy heavy particles striking the chamber walls produce sputtering. The magnetic confinement suffer from frequent plasma instabilities, which result in a fast release of plasma energy on Plasma Facing Components. The ensuing thermal and mechanical actions produce material damage, erosion, thermal ablation and melting. Components lifetime is strongly limited by such extreme phenomena and require careful design and material selection to avoid unwanted maintenance stops and replacements. The main aim of this research activity is to evaluate the PFMs erosion due to thermal ablation, to understand how material properties are affected by plasma interactions and how correctly select PFMs, without relying simply on empiric correlations with limited validity. The main part of the performed work consist in the development of Molecular Dynamics and Monte Carlo Simulation aimed to evaluate the thermal properties of PFMs and to investigate how high energy electrons produced within the plasma carry energy towards tokamak chamber walls. The analysis of Plasma Material Interactions has been historically carried out by putting together experimental activity and empiric relationships accounting for complex physical effects in an approximate fashion. The current research activity wants to investigate such phenomena starting from the underlying physical basic principles and through a comparison with experimental data with minimum employ of empiric relationship.