In–out asymmetry of low-Z impurity deposition on the JT-60U divertor tiles

Low-Z impurity (7Be) on the JT-60U divertor tiles was analyzed to study the impurity behavior in the divertor region. The amount of the 7Be increased approximately one hundred times after B4C-tile installation in the outer divertor. The 7Be was probably produced by 10B(p,α)7Be nuclear reaction on the divertor tiles in the hydrogen experiment with ion cyclotron range of frequency heating. The 7Be was distributed asymmetrically in the poloidal and the toroidal direction. The highest 7Be concentration was found at the inner divertor whose boron content (B/(B+C) ∼ 20%) was lower than the B4C tiles (B/(B+C) ∼ 80%) of the outer divertor. This result may imply impurity transport from the outer divertor to the inner divertor.