Beryllium has applications in various environments which will (or already do) expose it to radiation which will result in the accumulation of helium gas and cause the displacement of atoms from their crystal lattice sites. Beryllium will be the material facing the plasma in the ITER magnetic-confinement nuclear fusion reactor currently under construction in France and titanium beryllide is being developed for use in the "pebble bed" design concept for the tritium-breeding blanket of the DEMO power plant which will follow ITER. In high-energy accelerator research, beryllium is being considered for components in proton-driven particle sources where it will experience even higher rates of helium accumulation than in nuclear fusion environments. This project will explore the effects of gas accumulation and displacement damage in beryllium and titanium beryllide using transmission electron microscopy with in-situ ion irradiation to simultaneously observe the microstructure whilst bombarding with an ion beam. By varying the temperature, ratio of gas implantation to atomic displacement rates and the irradiation dose, this project will build up a three-dimensional matrix of experimental data. Changes in the microstructure of a material determine how the performance of components change under the extreme environments described above. Therefore, these results will allow the ways in which the microstructure evolves under these conditions to be better understood and thus support the development of these important technologies.