ICRF antenna impedance measurements with voltage and current probes on EAST

Abstract

A new set of measurement system on the Experimental Advanced Superconducting Tokamak (EAST), based on voltage and current probes, is installed on transmission line between matching system and ion cyclotron range of frequencies antenna to measure the antenna input impedance. The data can be used for impedance-matching points optimizing, as well as coupling coefficient assessment by deducing the antenna coupling resistance from antenna input impedance. The measurement error of amplitude and phase difference show distinct impact on the coupling resistance. Generally, the amplitude measurement error has a small impact on coupling resistance, while the phase measurement error significantly affects the coupling resistance. Instead of using phase detectors, phases can be extract from the power measurements. Thus, the antenna input impedance and coupling resistance can be deduced from the amplitude of voltage probe, amplitude of current probe, as well as the antenna feeding power. on previous experiments, the impedance measurement technique based on voltage probes array is utilized to evaluate coupling resistances. In EAST 2016 campaign, the load coupling resistance calculated by using such two techniques were detected and the results showed agreement.