Assessing material migration through 13C injection experiments

To mimic a localized impurity source for materials migration studies, 13CH4 has been injected into AUG, DIII-D, JET, JT-60U and TEXTOR at a single location into repeat, well-characterized plasmas, making for much more interpretable data than campaign-integrated erosion and deposition. Such studies have shown convincingly that for single null configurations, material is likely to migrate from the wall to the inner divertor creating tritiated co-deposits there. It has also indicated that for an unbalanced double-null configuration similar to ITER's the sputtered wall material is likely to create co-deposits on the blanket wall rather than the divertor; this has implications for ITER tritium retention in Be co-deposits since the wall can only be baked to 240 °C. The location and magnitude of tritium co-deposition in the 1997 JET DTE was not as expected from the 1991 PTE. It is recommended that 13C or other tracer experiments be performed in ITER as early as possible.