Current status and plan of development of Nd:YAG laser Thomson scattering system in Heliotron J

Abstract

An Nd:YAG Thomson Scattering system has been developed in Heliotron J. The Thomson scattering system is used for an investigation of an improved confinement physics such as the edge transport barrier (H-mode) or the internal transport barrier of the helical plasma. The system has 25 spatial points with ∼10 mm resolution. Two high repetition Nd:YAG lasers (> 500mJ@50 Hz) realize the measurement of the time evolution of the plasma profile with 10 ms time intervals. The scattered light is collected with a large concave mirror (D=800 mm) with a solid angle of ∼80–100 mstr. The laser beam is injected from obliquely downward to upward, and obliquely backscattered light is detected. A multi-path Thomson scattering system is under development to measure anisotropic electron velocity distribution and to increase the accuracy of the density and temperature profiles. First, we have applied a double-path Thomson scattering system using a Faraday rotator to the Heliotron J. The clear backward and forward scattered lights are successfully detected. Now the system is upgraded to a multi-path system using a pockels cell. The final goal of the development is the system that has two pockels cells to separate the backward and forward scattered lights.