Localized density measurements on ASDEX using microwave reflectometry

Reflectometry is based on the propagation and reflection of probing waves in the inhomogeneous fusion plasma. Broadband swept systems have been recently developed for TORE SUPRA, ASDEX and DIII-D, and a multichannel narrowband system for JET. The ASDEX reflectometric system consists of three reflectometers in the frequency bands 18-26.5 (K-band), 26.5-40 (KA-band) and 40-60 GHz (U-band). Electron densities measurements can be performed in the region starting from the plasma radius close to the magnetic separatrix on to the gradient region (from 0.4 to 4.45x1013 cm-3). Broad band experiments were made with simultaneous swept operation of three reflectometers (2ms). Plasma density profiles and density perturbations have been measured for several plasma scenarios. Results are presented and the scope and the limitations of the evaluating techniques are discussed. (author) 7 refs., 5 figs