Capabilities of the ITER Upper Launcher for ELMy-H mode plasmas at low magnetic fields

Abstract

The capabilities of the ITER ECRH upper port launcher to drive a well localized current (co-ECCD) either at the q = 1.5 or at the q = 2 surface by injecting EC waves as first harmonic O-mode at the nominal frequency f = 170 GHz have been already explored for a number of ITER scenarios relevant for neoclassical tearing modes (NTM) stabilization. The analysis, made by including the hybrid scenario 3 and a low q scenario (scenario 5) as well as equilibrium and poloidal beta variations in addition to the Q = 10 reference scenario 2, explored a wide range of relevant surfaces with different kinetic data for each scenario. "Optimal" toroidal and poloidal injection angles for application of co-ECCD on the relevant flux surfaces have been identified for the two rows of mirrors, and performance evaluations by taking into account several beam parameters have been carried out. However, the analysis so far has been done only for one specific value of the vacuum toroidal magnetic field (B0 ∼5.3 T at R0 = 6.2 m). In this work the capabilities to drive efficient and well localized co-current for a range of relevant surfaces in ELMy-H mode ITER plasmas at lower magnetic fields are explored by an updated version of the Milano beam tracing code. On the beam trajectories fully relativistic EC absorption and CD are calculated at both first and second harmonic. The changes of the "optimal" launch angles as a consequence of the shift of the resonance to lower values of major radius are shown. The range of magnetic fields for which power deposition and current drive at relevant surfaces becomes impossible for EC waves injected from upper launcher as first harmonic O-mode is pointed out. Further, the effectiveness of the upper launcher for stabilization of (3,2) and (2,1) NTM is investigated in the range of magnetic fields where EC waves at f = 170 GHz should be injected as second harmonic X-mode.