The National Spherical Torus Experiment-Upgrade poloidal high-k scattering system pitch angle design modifications.

A 693 GHz, eight-channel, poloidal high-k (k refers to wavenumber) collective scattering system is under development for the National Spherical Torus Experiment-Upgrade device. It will replace the previous 280 GHz, five-channel, tangential scattering system to study high-k electron density fluctuations, thereby providing a measurement of the kθ-spectrum of both electron temperature gradient and ion temperature gradient modes. A tool is under development to calculate the wavenumber that exists in the presence of strong magnetic pitch angles. We use this tool to motivate a new receiver optical design for significantly improved performance, details of which are presented herein.