A detailed comparison of antenna impedance measurements at ASDEX Upgrade with the ICRF antenna code TOPICA

New antenna diagnostics on ASDEX Upgrade, in the form of voltage and current probe pairs on the feeding lines of each ICRF antenna, close to the input ports, has made it possible to study in detail the behavior of the ASDEX Upgrade two-strap antenna under changing loading conditions, and compare these measurements with results of simulations using the TOPICA code. The present work extends previous studies by using the input impedance (more precisely, the complex voltage reflection coefficient Γ) on each antenna port for comparison, instead of the more commonly used loading resistance or coupled power. The electron density profiles used for the simulation were reconstructed from DCN interferometer and Lithium beam emission spectroscopy measurements, ELMsynchronized and averaged over time intervals from 10 to 200 ms depending on the case; 112 cases were compared from seven ASDEX Upgrade discharges with widely different plasma parameters and two operating frequencies (30 and 36.5 MHz). Very good agreement in |Γ| is found with the measurements on antenna 3 (< 3% averaged over a shot), good agreement is found with antennas 1 and 2 (< 10%); the code reproduces the correct trend in loading resistance RL in a significant majority of cases, although the discrepancies in the absolute values can be rather high (up to ∼ 50%) due to high reflection. Sources of discrepancy are discussed. PACS numbers: 52.50.Qt TOPICA study on ASDEX Upgrade 2