Analysis of dynamic matching networks for the ICRF system at ASDEX Upgrade

The ICRF (Ion Cyclotron Range of Frequencies) system, used to heat the plasma of ASDEX Upgrade, consists of RF generators, 3 dB hybrids, coaxial transmission lines, matching networks and inductive loop antennas. The maximum power achievable by the generator strongly depends on the amplitude and phase of the reflection coefficient. Hence, matching of the antenna input impedance to the generator output impedance is essential for the ICRF heating system. The coupling between the ICRF antennas and the plasma is subject to relatively fast variations (few ms). The changes are caused by the modification of plasma edge conditions, such as L–H mode transitions, gas puffing or ELMs (Edge Localized Modes). These variations change the impedance of the ICRF antennas. For optimal operation of the ICRF system, a continuous, and fast matching is therefore preferable. A MATLAB® based simulation tool has been developed to analyse matching networks for the ICRF system at ASDEX Upgrade. The program is highly flexible, and can solve the matching calculations for different conditions and configurations of the system. The results are presented in a Smith chart.