MD Simulation of High Energy Cascades and Damage Accumulation in β-SiC in Inertial Fusion Conditions

An extreme condition in Inertial Fusion Energy (IFE) reactors will be the very high neutron dose rate from each burst of high gain targets. The effect of pulsed damage on the structural materials of the reactor chamber needs to be examined and its actual importance carefully assessed.

A first calculation of neutron spectra and intensities in one burst of directly driven target (pR ≈ 4 g.cm⁻², 3 Hz) yields, for a ≈ 500 MJ shot of neutrons, a rate of ≈ 7 × 10²⁰ n.s⁻¹, the total time of deposition on the chamber walls being of ≈ 1 μs. This corresponds to a collisional parameter of 0.1 dpa/burst (in Fe), which gives an average damage rate of ≈ 3.8 dpa/year. The evolution in time of collisional damage is also presented.

Our work focuses on cubic silicon carbide (β-SiC) as a base for the next generation of low-activation materials. The Molecular Dynamics (MD) code MDCASK allows the description of the interaction of high energy recoils with the SiC lattice, by using a modification of the many-body semi-empirical inter-atomic Tersoff potential, merged with a repulsive binary potential obtained from ab initio calculations. A new assessment of previous works is presented. Preliminary values of threshold displacement energies are given and the observation of recombination barriers is reported. As a first step for a future intra- and inter-pulse damage study, by means of Kinetic Monte-Carlo (KMC) diffusion calculations, 3 and 5 keV Si-recoil-induced cascade simulations are analysed, discussing excitation and defects' characteristics in both sub-lattices: differences with respect to earlier works are found. Finally, the simulations of accumulations of up to 25 recoils of 500 eV and 1 keV are examined, in order to get a deeper insight into the damage state produced inside the material by intensive and prolonged irradiation in the absence of self-annealing.