Performance of the ITER ICRF antenna plug as expected from TOPICA matrices

The performances of the present ICRF antenna plug design is evaluated by means of the TOPICA 24×24 matrix for plasma loading supplemented by 4-port junction (4PJ) matrices. For their interpretation these results are compared with a cruder modeling by the semi-analytical code ANTITER II. From this analysis we conclude: (1) The broadbanding effect of the service stub on the response of the 4PJ made for one triplet is maintained for the complete array for all the heating and current drive phasings. (2) For a given maximum voltage of the 8 feeding lines the radiated power capability is roughly constant in the entire frequency band. (3) The power capability of the array is significantly dependent on the distance of the antenna to the Last Closed Flux Surface, the density profile in the scrape-off layer (SOL) and on the toroidal and poloidal phasings. The dependence on phasing is stronger for wider SOL (4) For a not too optimistic plasma density profile (Sc2 shortl7) a power capability exceeding 20 MW is only obtained for the 00 ππ heating toroidal phasing and for the co-current drive phasing in the upper part of the frequency band for a maximum voltage in the complete system of 45 kV. (5), On account of the plasma gyrotropy the quadrature poloidal phasing introduced by hybrid feeding must excite waves propagating upwards in the ITER configuration to obtain the best coupling, (6) The large power capability difference between opposite current drive phasings is attributed to the coupling between the toroidal and poloidal phasings induced by the poloidal steady magnetic field.