Speaker
Mr
Young-Gi Kim
(Seoul National University)
Description
A Nd:YAG laser Thomson scattering (TS) system has been developed on Versatile Experiment Spherical Torus (VEST) for measurement of the electron temperature and density of the core plasmas. To overcome the limitations of relatively low laser energy of 0.6 J/pulse for measuring low electron density of $\sim10^{18}$ m$^{-3}$, the system is delicately designed to improve a signal-to-noise ratio by using high transmission optical components. For effective collection of the scattered photons, the collecting lens have been designed for matching to detectors and the optical fiber of large etendue. Additional components for reducing the stray light and filtering H-alpha emission have been installed since the large background signal comparable to TS signals influence on reliable measurement. In addition, a synchronous circuit has been developed to reset the oscillation timing of the laser to synchronize the 10 Hz repetition rate with the VEST plasma whose pulse duration is $\sim 20$ms. An absolute calibration for the system was performed by Rayleigh scattering in various pressures of nitrogen. The electron temperature and the electron density are deduced from the TS signals using Bayesian statistics with assumption that the random noise follows the Gaussian distribution. The tendency of the measured electron properties are compared with the properties measured by triple Langmuir probes.
Primary author
Mr
Young-Gi Kim
(Seoul National University)
Co-authors
Mr
Doyeon Kim
(Seoul National University)
Mr
HyunYeong Lee
(Seoul National University)
Dr
Jong Ha Lee
(National Fusion Research Institute)
Mr
Min-Gu Yoo
(Seoul National University)
Prof.
Yong Hwang
(Seok)
Prof.
Yong-Su Na
(Seoul National University)
