A tritium permeation ‘short cut’ for plasma-facing components of fusion reactors

Abstract

In ITER and other fusion reactors, plasma-facing components (PFCs) will be subjected to intense plasma/neutral fluxes and tritium (T) permeation issue will be raised. In the present work, first-of-a-kind experiments on hydrogen isotope (D) transport through ITER-like PFC mock-ups have been demonstrated in a linear plasma facility. 8 mm thick W tiles with 0.5 mm gaps are installed on structural materials and exposed to D plasmas. The angle between the gaps and the magnetic field line is set to be 5° to ensure the structural materials behind W are not exposed to charged D ions from plasma. When plasma is started up, the sample mock-ups are found to be penetrated by D within tens of seconds, suggesting that D can penetrate through heat sink of PFCs without passing through the thick W armor, i.e. the gaps act as a hydrogen isotope leakage ‘short cut’. To make a straightforward comparison of permeation flux for these materials, direct D plasma-driven permeation (PDP) experiments through W and structural materials are performed as well. The measured permeated D fluxes through structural materials are found to be orders of magnitude higher than that of W, indicating T transport from the gaps of PFCs may contribute a remarkable fraction of total leakage in reactors. In the latter part of this paper, a solution to address the permeation issue is proposed.