Overview of High-k Scattering Diagnostics on NSTX and NSTX-U

Electron-gyro scale turbulence, e.g. driven by the Electron Temperature Gradient (ETG), has been proposed as a potential candidate for driving anomalous electron thermal transport, a major problem for magnetic confinement fusion. NSTX and NSTX-U provide a unique laboratory for studying electron-scale turbulence and its relation to electron thermal transport due to their low toroidal field, high plasma beta, low aspect ratio and large ExB flow shear. Electron-gyro scale turbulence has been successfully measured in NSTX using a unique high-k$_r$ microwave scattering system, providing the first direct evidence of ETG turbulence in STs and detailed studies of parametric dependence of electron-scale turbulence. However, the high-k$_r$ microwave scattering system could not capture the predicted ETG spectral peak. Thus a new high-k$_\theta$ FIR scattering system is being implemented for NSTX-U. We will present an overview of the scattering systems on NSTX and NSTX-U, including physics designs, capabilities and recent physics results. We will also discuss methods to achieve radially localized scattering measurements.