Comparison of Fuel Retention in JET between Carbon and the ITER-Like Wall
Long term fuel retention experiments have been performed in JET with the ITER- Like Wall (JET-ILW) and compared with references in carbon in ohmic, L and H-mode conditions. The long term retention is evaluated through global gas balance for series of repetitive pulses (10 to 25) carried out over a full day of experiments. For ohmic plasma, a retention rate of 3-5¥1019Ds-1 is obtained which has to be compared to 1-2¥1020Ds-1 in carbon. For L mode, the retention exhibits also a drop from 1¥1021Ds-1 to 4-8¥1019Ds-1. Finally for Type III and type I ELMy H-mode, the retention decreases from 1.4¥1021Ds-1 to 7.7¥1019Ds-11 and from 1.7¥1021Ds-1 to 2.7¥1020Ds-1 respectively. Retention rates with the JET-ILW exhibits a decrease by a factor 10 compared to carbon attributed to a reduction of carbon impurities and less fuel content in Be codeposition. Compared to carbon, extrapolation to ITER exhibits an increase of a factor of 10 of the predicted number of full performance 400s discharge before reaching the safety limit of 700g of T retention.