Monostatic density profile reflectometry measurements on DIII-D and relevance to ITER low-field-side reflectometer*

Typically, density profile reflectometry systems employ bi-static antenna configurations to avoid the deleterious effects caused by spurious reflections. However, there are potential advantages, particularly on ITER, if a monostatic antenna configuration could be employed. Such a configuration would allow either a reduction in the number of waveguides necessary to satisfy measurement requirements or an expansion in capability assuming a fixed number of antennas. To address the feasibility of this configuration, a monostatic reflectometer operating from 33 to 75~GHz in both O-and X-mode has been designed, fabricated, installed and tested on DIII-D. Preliminary results appear positive with measured profiles in good agreement with Thomson scattering. More extensive tests are underway, including investigation of the ability to accommodate plasma height variations using a fixed antenna. System design and preliminary results will be presented.