Progress in the analysis of the cavity resonances in the ITER ICRF antenna port plug

The ITER ICRF antenna plug [1, 2] can exhibit resonances at specific frequencies, some of them in the relevant range of frequencies for IC heating. These resonances have been identified as eigenmodes of the coaxial cavity, where the array plays the role of inner conductor [3], that can substantially increase the level of electric fields within the cavity as well as the level of RF losses. As no grounding solution is considered, RF probes should be installed to monitor the RF fields in the port plug cavity and additional simulations of a realistic magnetized plasma are required to properly assess the integration (position, orientation) and their effectiveness. Several numerical tools are available and have been extensively used to simulate the ITER ICRF antenna, such as TOPICA [5] or CST Microwave Studio (MWS [6]), but none of these codes allow to combine realistic geometries, realistic magnetized plasma profiles, and lossy materials. In this paper we pursue the effort started in [8] where a method based on a modal analysis in the cavity was introduced to decouple solving the computationally intensive plasma facing front of the launcher from the cavity. The method reproduces the TOPICA electric fields (with gyrotropic plasma effects) obtained in a given vertical reference plane, in a MWS cavity (including lossy materials) using the multimodal scattering matrix of the cavity obtained with MWS. This method is here applied to several realistic ITER plasma profiles. The recently extracted magnetic fields [9] from the TOPICA modeling results, provide an alternate way to compute the excitation spectrum of the cavity and therefore allow to confirm our results. Accurate levels of RF losses can then be obtained from various plasma profiles and excitation of the antenna straps.