Speaker
Young-Gi Kim
(Department of Nuclear Engineering)
Description
A Thomson scattering(TS) system is developed and commissioned for measuring and analyzing spatial profiles of electron temperature(Te) and density(Ne) of Versatile Experiment Spherical Torus(VEST). Since the estimated Ne of VEST plasma is ~5x101818m-3-3 which is lower than typical Ne in other tokamaks, each part of the system is carefully designed to maximize the number of collected photons. The system consists of 3 parts such as a novel multi-pass laser injection system, collecting optics, and a polychromator. The multi-pass scheme of a laser injection system including a Faraday rotator and a half-wave plate rotates 90 degrees of the plane of polarization in two roundtrips of a laser beam. The main purpose of this scheme is to achieve a high signal to noise ratio by rejecting the stray light signal or background noise using one laser pulse. The collecting optics comprising a vacuum window and two aspheric lenses is designed for measuring TS signals at the 5 different spatial points with R=0.4m as the center of the VEST device and for maximizing the collecting efficiency by matching the acceptance solid angle of collecting lenses with the numerical aperture of optical fiber. A shutter is installed to protect the collecting window from being coated during the glow discharge cleaning which can cause decreasing window transmittance. The polychromator used for VEST is the same type of KSTAR and is equipped with new set of bandpass filters for measuring Te in VEST. The number of polychroamtors will be prepared up to 5 for simultaneous multi-point measurement. As the first stage of development of the TS system, the TS and Rayleigh scattering signals at the single point(R=0.4m) are measured. We will discuss the result of our measurement and the novel multi-pass optical arrangement scheme.
Co-authors
H.Y. Lee
(Department of Nuclear Engineering, Seoul National University, Seoul, South Korea)
J. Lee
(Department of Nuclear Engineering, Seoul National University, Seoul, South Korea)
J. Wang
(Department of Nuclear Engineering, Seoul National University, Seoul, South Korea)
J.H. Lee
(National Fusion Research Institute, Daejeon, South Korea)
K. Cho
(Department of Physics, Sogang University, Seoul, South Korea)
W.-K. Ahn
(Department of Physics, Sogang University, Seoul, South Korea)
Y. Hwang
(Department of Nuclear Engineering, Seoul National University, Seoul, South Korea)
Y.S. Na
(Department of Nuclear Engineering, Seoul National University, Seoul, South Korea)
Young-Gi Kim
(Department of Nuclear Engineering, Seoul National University, Seoul, South Korea)
