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 ³He 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 ³He 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 ³He ICRF heating scenario the impurity content and the plasma energy loss through radiation was higher than for the fundamental hydrogen heating scenario.