Design of a Thomson scattering diagnostic for the SMART tokamak

We describe the design of a Thomson scattering (TS) diagnostic to be used on the SMall Aspect Ratio Tokamak (SMART). SMART is a spherical tokamak being commissioned in Spain that aims to explore positive triangularity (PT) and negative triangularity (NT) plasma scenarios at a low aspect ratio. The SMART TS diagnostic is designed to enable a wide range of electron temperature (1 eV to 1 keV) and density (0.5 - 10 $\times 10^{19} ~\rm{m^{ - 3}}$) measurements. A 2Joule laser operating at 1064 nm will be used to probe the electron temperature and density of the plasma. The laser is capable of operating in the burst mode at 1kHz, 2kHz, and 4kHz to investigate fast phenomena or at $30$ Hz to study 1 sec (or more) long discharges. The scattered light will be collected over an angular range of 60-120 degrees at 28 spatial points in the midplane covering the core region and edge plasma on both the low-field side (LFS) and the high-field side (HFS). Simulation data is used to determine the optimum location of Thomson scattering measurement points to effectively resolve the edge pedestal in the LFS and HFS regions under different triangularity conditions. Each scattering signal will be spectrally resolved on five wavelength channels of a polychromator to obtain the electron temperature measurement. We will also present a method to monitor in-situ laser alignment in the core during calibrations and plasma operations.