Study of the coupling of distributed ICRH antenna & of its optimization for heating of large machines as DEMO

Traveling Wave Antennas (TWA) sections constituted by toroidal arrays of inductively coupled straps are considered for the ICRF heating of DEMO. They are mounted in resonant ring(s) configuration to obtain the appropriate feeding, matching and load resilience conditions [1]. On top of the minimization of the distance plasma-wave cutoff their coupling conditions can be optimized by (i) the increase of the total strap number, (ii) the choice of a radiated power spectrum centered on an as low as possible |k| allowing still single pass absorption and avoiding coaxial modes excitation, (iii) the largest possible effective strap length l_str with uniform current amplitude. It is shown that a significant power capability increase with respect to the ITER antenna can be obtained for the same radiating surface and plasma profile mainly due to the absence of vertical septa between the straps.