Analysis of the ASDEX Upgrade 3-strap antenna with TOPICA code: Curved vs. flat 3D geometry

Before the 2015/2016 experimental campaign, the ASDEX Upgrade (AUG) 2-strap ICRF antennas with tungsten-coated limiters were replaced by 3-strap antennas. The main goal of the 3-strap launcher was to reduce the release of tungsten (W) in order to improve the ICRF operation, which appeared to be troublesome after the all-W wall installation [1]. In this paper, we analyse the behaviour of the 3-strap antenna with the help of TOPICA code [2], a numerical tool able to take into account a realistic antenna geometry and an accurate plasma description. By loading an experimental plasma profile from the AUG campaign, we characterize the antenna both in terms of input parameters and of radiated fields. In particular, we compare TOPICA results obtained with a simplified 3D flat model adopted during the design phase with the exact 3D curved geometry installed on the AUG experiment. In particular, the curved model predicts a lower coupling to plasma and higher RF electric fields with slightly different distribution in front of the launcher. The capability to include a fully 3D curved model is of great importance to correctly account for all geometrical effects on the antenna performances. The advantages and disadvantages of both geometrical representations are eventually outlined, trying to estimate how the curvature of the antenna can affect code predictions. Comparisons between measured experimental results and simulated ones are presented in [8].