Structure, morphology and deuterium retention and release properties of pure and mixed Be and W layers

Abstract

Deuterium retention and release behavior were investigated in this study, for thin layers of beryllium, tungsten and mixed beryllium/tungsten layers which are of concern for next-generation thermonuclear fusion devices like International Thermonuclear Experimental Reactor. The layers were resulted from deposition with Thermionic Vacuum Arc technology by using two different ion acceleration voltages 0 V and -700 V respectively and were subsequently implanted by exposure to a steady-state deuterium plasma with ion energies of 240 eV/D for D3 and 360 eV/D for D2 at a specific fluency of 2.85×1020 m-2 *s. Morphology studies indicate that it is strongly influenced by layer composition and by the ion acceleration voltage applied in-situ during layer deposition. Structural analysis shows the presence of a polycrystalline W metallic phase and also highlights a dependence between tungsten crystallite size and Be/W atomic ratio. Thermal desorption spectra show that the nature of deuterium trapping states in layers are significantly affected by the beryllium/tungsten ratio and deposition conditions. On the other hand, the amount of deuterium in mixed layers is lower than in pure beryllium layers indicating that W is mitigating D binding states. Also, layers deposited with -700 V show a decreased retention compared to their counterparts deposited at 0 V, indicating that retention in ITER will be influenced by re-deposited layers properties such as microstructure and compactness.