Improvement of electron temperature and density accuracy in Thomson scattering diagnostics by an accumulation of 100 laser pulses within 5 milliseconds

In order to measure the electron temperature and density in high-electron-temperature and low-density plasmas, improvement of the signal-to-noise ratio of the Thomson scattering measurement signal in the Large Helical Device has been tried. One hundred laser pulses of about 1 J in 5 ms were injected at 50 mu s intervals into plasmas in an almost steady state. By averaging the scattered signals obtained from the same plasma and the same location, the noise in the signals and the error in the background level were also reduced. When the number of signals to be averaged was large, the scattering of the electron temperature profile was small and the magnitude of the error also became small.