Assessment of the ITER electron cyclotron upper launcher capabilities in view of an optimized design

The 24 MW ITER electron cyclotron (EC) heating and current drive (H and CD) system, operating at 170 GHz, consists of one equatorial and four upper launchers (UL). The main task of the UL will be the control of magneto-hydrodynamic activity such as neoclassical tearing modes (NTMs) at the q = 3/2 and q = 2 surfaces and sawteeth at q = 1, but it will also be needed for current profile tailoring in advanced scenarios and to assist plasma break-down and L- to H-mode transition. Moreover, it is required to be effective both when ITER will operate at nominal and reduced magnetic field magnitude. Here the performance of the UL has been assessed through the study of the full temporal evolution of different scenarios, including the reference ITER 15 MA H-mode plasma, a half-field case at 2.65 T and a steady state scenario. The ECCD efficiency has been evaluated for a wide range of injection angles, deriving the optimal angles and the power required for NTMs stabilization with simplified criteria. An injected power ranging from 3 MW to 9 MW should be sufficient to control NTMs in the flat-top phase of the scenarios considered here. The result of the analysis shows that the EC system maintains a good performance level even at intermediate values of the magnetic field, between the nominal and the half-field value. The analysis has also allowed to evaluate the adequateness of the available steering range for reaching the rational surfaces during all the phases of the discharge and to quantify the steering sensitivity to shifts of the target or aiming errors. The result is an assessment of the UL design requirements to achieve the desired functionalities, which will be used to drive the optimization and finalization of the UL design.