ICRF scenarios for ITER's half-field phase

The non-active operation phase of ITER will be done in H and ⁴He plasmas at half the nominal magnetic field, B ₀=2.65T. At this field and for the given frequency range of the ICRF system (f=40-55MHz), three ICRF heating scenarios are available a priori: (i) Fundamental ICRH of majority H plasmas at f≈40MHz, (ii) second harmonic (N=2) ³He ICRH in H plasmas at f≈53MHz and (iii) fundamental minority H heating in ⁴He plasmas at f≈40MHz. While the latter is expected to perform well for not too large H concentrations, the heating scenarios available for the Hydrogen plasmas are less robust. Recent JET experiments performed in similar conditions to those expected in ITER's half-field phase confirmed the low performance of these two scenarios and numerical simulations have shown that the situation is not much improved in ITER, mainly because of the rather modest plasma temperature and density expected in its initial operation phase. A summary of the main experimental results obtained at JET followed by numerical predictions for ITER's half-field ICRF heating scenarios will be presented.