Gas Exhaust Study by RGA in JET after Disruptions and Impurity Seeding
ITER will start with a full tungsten divertor and will operate with type I ELMy H-mode. W erosion by impurities will determine the divertor target tiles lifetime. This erosion will be caused during semi-detached divertor operation, mainly by ELMs carrying both intrinsic impurities such as Be, O, and C; and seeded impurities applied to reduce divertor heat loads and induce inter-ELM detachment. Ar or Ne will also be injected during Massive Gas Injection (MGI) for disruption mitigation. JET with its ITER-Like-Wall (ILW) offers a unique insight into the gas impurity concentration in the ITER material mix: Be and W in the absence of C. The temporal evolution of the impurity concentration can be followed during a single discharge or a full day of operation, up to 35 discharges. The experience from JET can be used to extrapolate the impact of impurities on ITER plasma operation. Gas impurity concentration is studied utilizing the magnetically-shielded Residual Gas Analyzer (RGA) of JET sub-divertor. The temporal behavior of impurities released after MGI-mitigated and unmitigated disruptions during seeded and non-seeded discharges will be analyzed. MGI-induced disruptions will also be accessed as a method to control impurity levels. This study will be focused on nitrogen, most probable seeding gas, which has the drawback to be retained in tungsten, produce tritiated ammonia, etc.