Validation of a 3D/1D Simulation Tool for ICRF Antennas

TOPICA is an innovative tool for the simulation of the Ion Cyclotron Radio Frequency (ICRF) antenna systems that incorporates commercial‐grade graphic interfaces into a fully 3D self‐consistent description of the antenna geometry and an accurate description of the plasma; it can be considered as a “Virtual Prototyping Laboratory” to assist the detailed design phase of the antenna system. Recent theoretical and computational advances of the TOPICA code has allowed to incorporate a CAD drawing capability of the antenna geometry, with fully 3D geometrical modeling, and to combine it with a 1D accurate plasma description that takes into account density and temperature profiles, and FLR effects; the profiles are inserted directly from measured data (when available), or specified analytically by the user. The coaxial feeding line is modeled as such; computation and visualization of relevant parameters (input scattering parameters, current and field distributions, etc.) complete the suite. The approach to the problem is based on an integral‐equation formulation for the self‐consistent evaluation of the current distribution on the conductors. The environment has been subdivided in two coupled region: the plasma region and the vacuum region. The two problems are linked self‐consistently by representing the field continuity in terms of equivalent (unknown) sources. In the vacuum region all the calculations are executed in the spatial (configuration) domain, and this allows triangular‐facet description of the arbitrarily shaped conductors and associated currents; in the plasma region a spectral representation of the fields is used, which allows to enter the plasma effect via a surface impedance matrix; for this reason any plasma model can be used, and at present the FELICE code has been adopted; special techniques have been adopted to increase the numerical efficiency. The TOPICA suite has been previously tested against assessed codes and against measurements of mock‐ups and existing antennas. This work is devoted to an extensive set of comparisons between measured and simulated reflection coefficients (magnitude and phase), both in vacuum and with plasma during ALCATOR C‐MOD operation. The comparison demonstrates a very good agreement, leading to a validation of TOPICA as a predictive tool.