Development of a Thomson Scattering System in the TST-2 Spherical Tokamak

The Thomson scattering system in the TST-2 has been upgraded to improve the reliability and accuracy of measurements. The signal intensity increased because of a new high-energy (1.6 J) laser. A large-numerical-aperture (N.A.) fiber was tested, and it was found that a 6-m-long fiber can be used without significant transmission loss. With the upgraded system, the typical central electron temperature and the electron density for ohmic discharges (with a plasma current of 60 kA) are 150 eV and 1.5 × 1019 m−3, respectively. The temperature profile has a maximum near the center of the plasma.