ITER low-field-side density profile reflectometer: design challenges and optimization*

Ensuring the availability, reliability and accuracy of profile, MHD and turbulence measurements in ITER represents a significant challenge. In contrast to optically-based diagnostics, millimeter-wave systems are well-suited to the harsh burning plasma environment. However, a number of design issues remain including cutoff layer modifications due to relativistic effects at high temperatures, diagnostic availability/accessibility for a range of operating conditions/plasma positions, and minimization of phase errors introduced through antenna coupling/mode conversion in overmoded corrugated waveguide. Design issues such as this have been addressed through analysis coupled with laboratory measurements. An optimized conceptual design of the front-end antenna configuration has been generated together with an assessment of the expected accuracy of the density profile measurement.