Impurity studies for the ITER half-field ICRF heating scenarios in hydrogen plasmas on JET

Two ion cyclotron range of frequencies (ICRF) heating scenarios, proposed for the non-activated half-B-0 phase of ITER in hydrogen plasmas, were investigated on the JET tokamak. This paper we present a detailed study of the impurity content in plasma when the fundamental H and the 2nd harmonic He-3 ICRF heating scenarios are realized. The ICRF conditions for those heating scenarios on ITER - i.e. the frequency of 42 MHz for the fundamental H and 53 MHz for the 2nd harmonic He-3 heating, and the magnetic field B-0 = 2.65 T - were closely reproduced in dedicated experiments on JET. The impurity content of the plasma was determined by means of the spectroscopy in the VUV range. The release of C and Ni impurities during the ICRF heating is presented as a function of the total ICRF heating power supplied in those heating scenarios. The contribution of the Ni impurity to the effective charge of the plasma, Z(eff), and the plasma dilution are estimated. We find that for the He-3 ICRF heating scenario the impurity content and the plasma energy loss through radiation was higher than for the fundamental hydrogen heating scenario.