Investigating energy transport and equilibration under non-equilibrium conditions

Fusion power holds the key to a plentiful supply of clean, cheap energy, but there are formidable technical problems to be overcome before such dreams become a reality. One such problem is the selection of materials able to withstand the intense flux of energy and neutrons from the fusion reaction. The plasma-facing materials are subjected extremely high energy fluxes, therefore it is essential that heat is rapidly transported away from the surface material to prevent surface temperature rising above the melting temperature. Heat energy is transported in solids by lattice vibrations and the movement of electrons. In metals, under normal conditions, most of the heat is transported by the electrons as they can move easily through the lattice. However only part of the energy deposited in the first wall of fusion power plants goes to the electrons, the rest is deposited in the lattice. The system is a long way from equilibrium, with the lattice having a different temperature from the electrons and the energy is transported both by electrons and by lattice vibrations. Interactions between the atoms and the electrons gradually drive the system to equilibrium, with the electrons and the lattice having the same temperature.We propose to investigate energy transport under such highly non-equilibrium conditions, such as those found at the first walls of fusion power-plants, using simulation techniques. The common technique of Molecular Dynamics will be extended to include the effects of energy transport by the excited electrons and the coupling between the lattice and the electrons. This will help us to estimate the conditions under which we can expect surface melting at the first walls of fusion power plants and to suggest methods that will prevent surface melting occurring.