Helium beam diagnostics for the estimation electron temperature and density in SST-1

Supersonic helium beam Diagnostics is used to estimate edge electron density and temperature in tokamaks. Ratio of line emission intensities from neutral helium is used to estimate electron temperature and density. Temperature is estimated from the ratio of intensities (728.1 nm /706.3 nm) whereas density is estimated from ratio (668.1 nm/728.1 nm). We have designed and tested a supersonic helium beam injector for edge plasma temperature and density for SST-1 tokamak. The system consists of a supersonic injector and an imaging system. The emission is collected by the imaging system and optical fibers and an EMMCD coupled spectrograph is used to record the spectra from various spatial locations. The spatial resolution is around 5 mm. In a recent campaign in SST-1, we tried to estimate these parameters using the residual helium after the helium GDC. The spectrometer and detection system was calibrated and signal was optimized. The spectra were good enough to use these helium lines to estimate electron temperature and density with an integration time of 10 ms. The observed line ratios are compared with the line ratios obtained from CR model/Atomic Data and Analysis Structure (ADAS) to get an estimate of electron temperature and density. The estimated electron density is in the range of 5 x 10¹¹ - 2 x 10¹² cm^-3 and electron temperature 30-55 eV. The obtained parameters provide reasonable estimates when compared with other diagnostics considering the diffusion and ionization of neutral helium inside the tokamak. (author)