Comparison of tritium retention and carbon deposition in JET and JT-60U

Profiles of T retention in the Mark IIA divertor of JET and H/D and T retention in the W-shaped divertor of JT-60U are compared. Hydrogen (H, D and T) is retained in carbon deposited layers with nearly constant concentration throughout the layers, except high energy triton directly impinging into more than 1 μm in depth. However, carbon deposition profiles and hydrogen retention are strongly influenced by geometrical structure of the divertor and tile alignment as well as by magnetic field lines. Carbon deposition on the divertor base tile in JET shows stripes parallel to magnetic filed lines, suggesting a direct plasma deposition process. In JT-60U, the temperature of the co-deposited layers during operation plays critically important role on the hydrogen retention. It seems possible to reduce tritium inventory significantly by increasing the surface temperature of the plasma facing components.