Fusion tritons and plasma-facing components in a fusion reactor

We would like to discuss the role that 1 MeV tritons produced in deuterium-deuterium fusion reactions might play in a long-pulse or steady-state fusion reactor. Albeit a small minority in quantity compared to the fuel tritium, the fusion tritons have significantly longer penetration length in materials and can have detrimental consequences for the integrity of the components. Because deeply deposited atoms are not easily removed from the plasma-facing components, the fusion tritium inventory in a steady-state device is expected to be limited only by decay. Furthermore, unlike fuel tritium, it is not evenly distributed on the plasma-facing components. We conclude that, of the materials considered here, tungsten appears better than carbon or beryllium in this respect. Nonetheless, 1 MeV tritons from deuterium fusion should not be neglected when making material choices for ITER and, especially, for future fusion reactors. In particular, studies on the bulk effects of deeply penetrated tritium in tungsten are urgently needed if metal-wall reactors are considered for the future. This is an interdisciplinary problem needing the attention of material scientists and plasma physicists. (authors)