Plasma Isotopic Change Over Experiments in JET Under Carbon and ITER-Like Wall Conditions
Starting with a wall loaded by H2, change over experiments from H2 to D2 have been carried out in JET-ILW. A series of 13 repetitive pulses (cumulating 215s in divertor configuration) have been performed under conditions of: Ip = 2.0MA, BT = 2.4T, <ne> = 4.5¥1019m­3 with a constant gas injection of 3.0¥1021Ds­1 and 0.5MW of auxiliary heating by ICRH in L-mode. Gas balance analysis shows that the total amount of H removed from the wall is in the range of 3¥1022D compared to 2x1023D for JET-C. This is consistent with the faster decay of the H plasma concentration and the drop of the retention also by a similar factor when removing all the carbon components. Isotopic plasma wall changeover is also demonstrated to allow for removal of some D/T from the device. However, since plasma change over also contributes to long-term retention by codeposition, in ITER, change over in between each discharge might not be effective to reduce the fuel retention on the long-term.