Recent Progress of the LHD Thomson Scattering System

The Large Helical Device (LHD) Thomson scattering system measures electron temperature and density profiles of LHD plasmas along the LHD major radius at a horizontally elongated section. The LHD Thomson scattering system has an oblique backward-scattering configuration. The number of observation points and typical spatial resolution are 144 and 17 mm, respectively. The temporal sampling frequency is 10 to 100 Hz. Measurable temperature and density ranges are T_e = 5 eV to 20 keV and n_e 10¹⁸ m^-3 , respectively. The LHD Thomson scattering system consists of several subsystems: laser system, light collection optics, polychromators, and data acquisition system. In the past decade, we have continued our efforts to improve the performance and reliability of the LHD Thomson scattering system through extension of measurable temperature and density ranges, Raman and Rayleigh calibrations for absolute density measurements, new laser beam positioning system, and plasma light monitor system for increasing data reliability. In this paper, we describe the recent progress of the LHD Thomson scattering system in detail.