Effect of poloidal magnetic field and cross-coupling on a set of traveling wave antenna sections for the ICRH of fusion reactor plasmas

A set of Traveling Wave antenna (TWA) sections has been proposed for the ICRF heating of the reactor in view to decrease the antenna power density. The reduction of the antenna voltage and associate electric field and current is compensated by the number of radiating straps. An upgraded version of the fast semi-analytical code ANTITER-II is used to model a set of TWA sections of any arbitrary number of radiating straps facing a low coupling plasma profile with their feeding system. Now it incorporates the effect of the non-alignment of the antenna to the total steady magnetic field (toroidal + poloidal) in front of it. The model incorporates the feeding of each section by a resonant ring circuit that recirculates its output power. The cases of straps grounded at one of their ends (L grounding) or in their center (T grounding) are also compared. The model is applied to the proposed TWA section layout for the ICRF heating of DEMO. It is shown that the antenna tilting affects mostly the poloidal radiating spectrum seen by the plasma. This effect increases with the absolute value of the k_// selected by the antenna system. The coupling reduction and the effect on the strap current and voltage distribution due to the tilting is compared with the ones resulting from the mutual coupling between the sections. The effects of the tilting for the expected q_edge value of the reactor and of mutual coupling between toroidally spaced sections remain weak. The effect of coupling between poloidally superposed sections can become large.