A lower hybrid current drive system for ITER

Lower Hybrid Current Drive (LHCD) is one of the four well proven H and CD systems on tokamaks. It is a key element of the present devices addressing the long pulse and steady-state issues, exhibiting a large current drive efficiency, and is fundamental for their inductive flux saving needs. All existing and new superconducting tokamaks (Tore Supra, HT-7, EAST, KSTAR, SST1, JT60-SA, ...) have or plan significant LHCD capability. Since the emergence of the close link between the current profile and the turbulent transport properties, a strong renewed interest was found for LHCD in Advanced Tokamak (AT) researches. JET, Tore Supra, HT-7, FTU, C-Mod make an extensive use of LHCD for AT research towards steady-state operation of fusion devices, as well as for the intermediate so-called Hybrid mode of operation, in which the plasma profile is slightly adjusted to mitigate the main limitations of the ELMy H-mode regime. LHCD will be crucial for the preparation of advanced modes of operation in ITER as the current ramp-up rates are expected to be slow, possibly preventing the establishment of AT scenarios. Finally, LHCD may help ITER increase the safety margins for long pulse operation of its superconducting poloidal coil system, as well as for the initial ramp-up phase of the low-q operation. Avoidance of high-li vertical stability limits is an additional contribution of LHCD under consideration. Though not part of currently planned construction phase, the ITER LHCD system, initially planned for AT and Steady-state studies during its second phase of operation, is now under consideration for an earlier delivery. This paper summarizes an appropriate work plan developed along this line, following recommendations by ITER STAC, after the ITER Design Review process. (author)