Thomson scattering diagnostics at the Globus M2 tokamak

The paper is devoted to the Thomson scattering (TS) diagnostics recently developed for the Globus-M2 spherical tokamak and prototyping the ITER divertor TS diagnostics. The distinctive features of the system are the use of spectrometers, acquisition system and lasers that meet the base requirements for ITER TS diagnostics. The paper describes the diagnostic system that allows precise measurements of TS signals, as well as the results of the first measurements of electron temperature and density in both central region of the plasma column and scrape-off layer. The system provides measurements of electron temperature $T_{e}$ in the range of 5 eV to 5 keV and density $n_{e}$ in the range of $5{\cdot}10^{17}{\div}3.25{\cdot}10^{20} m^{-3}$. The use of two ITER-grade probing lasers of different wavelengths (Nd:YAG 1064.5 nm and Nd:YLF 1047.3 nm) allows reliable measurement of $T_{e}$ in multi-colour mode, i.e., assuming that spectral calibration is unknown

Dense plasma source development and jet injection in Globus-M*

Progress in the development of a plasma jet source and its utilization for injection of hydrogen plasma and neutral gas jets into the Globus-M spherical tokamak are presented. The latest version of the high kinetic energy gas and plasma jet source with titanium hydride grains is described. Reproducibility of the gas jet generation was increased due to automatic loading of fresh grains into the source before every shot. It allows producing stable gas release for many discharges. Impurity radiation intensity from the plasma jet was decreased by more than 100 times by preliminary processing titanium hydrate grains and developing a new filter. The result of special experiments on two colliding jets is discussed. It was confirmed that the plasma jet recombines into a gas jet after it escapes the source edge and has a kinetic energy higher than the hydrogen ionization potential. Hydrogen plasma jet with low impurity content has a density up to 2 × 1022 m-3, a total number of accelerated particles (1-5) × 1019 and a flow velocity of ~ 200 km/s. It was used as an instrument for density control in Globus-M. Jet injection into deuterium plasma core during current plateau phase led to fast density increase in all spatial points of the plasma column including the plasma central region. Such injection allowed density doubling in the tokamak plasma. The model predictions are consistent with the experimental observations of the density raise recorded by the interferometer and Thomson scattering