Parametric study of one triplet of the ITER ICRH antenna by numerical modeling

Each of the two ITER ICRF antennas consists of a close-packed array of 24 straps arranged in a 6 poloidal by 4 toroidal array. Three poloidally adjacent straps (a "triplet" of straps) are fed together through a 4-port junction from one 20 Ohm feeding line. The complete array has to radiate 20 MW of RF power over a frequency range of 40 MHz to 55 MHz and for different toroidal phasings. The RF optimization of the antenna has been performed numerically on one triplet of straps (1/8th of the antenna) [1,2]. In parallel a number of reduced-scale mock-ups of one triplet of the ITER ICRH antenna were constructed in order to validate the results of the numerical optimization [1,3]. The aim of this work is primarily to benchmark the CST MWS® [4] numerical modeling against numerous measurements done on the mock-up of the 2007 design. Moreover MWS calculates the 3D distribution of the currents and of the fields of the triplet. Hence it gives the possibility to check the fields and current distributions resulting from the optimisation study of the ITER ICRH antenna triplet done by changing geometrical parameters of the straps and antenna box of the mock-up of 2007 design [1-3]. The considered parameters are: strap width, antenna box depth and vertical septum recess with respect to the front of the current strap. The impact of the presence of the Faraday screen is also evaluated. Excellent agreement between modeled and measured S parameters is obtained. Analysis of the fields and currents distributions on the straps is reported. Excellent current balance is confirmed.