Characterization of a microwave reflectometer for edge density profile measurements at the ICRH antenna on Wendelstein 7-X

A microwave reflectometer has been integrated into the ion cyclotron resonance heating (ICRH) antenna system of the Wendelstein 7–X (W7-X) stellarator to measure electron density profiles in the edge region of the plasma. The diagnostic operates in X-mode and is specifically designed to probe the plasma directly in front of the ICRH antenna, where local density conditions critically influence radio-frequency power coupling. Dedicated calibration procedures were developed to improve the data collection and analysis. Electron density profiles, reconstructed from the corrected beat frequencies, show good agreement with measurements from Thomson scattering and Alkali beam emission spectroscopy, validating the reflectometry measurement. The edge density profiles can be measured when ICRH power is injected and exhibit the expected response to global density ramp-up experiments. These results demonstrate the capability of the microwave reflectometer to provide reliable edge density measurements and establish a basis for future studies of ICRH plasmas in W7-X.