Double-pass Thomson scattering diagnosis on the TST-2 spherical tokamak device TST-2球状トカマクにおけるダブルパストムソン散乱計測

A double-pass Thomson scattering system, in which a laser pulse makes a round trip through the plasma, has been constructed. Using a fast detection unit, backward and forward scattering pulses in the signal can be resolved. Since these scatterings reflect electron temperature along different directions, electron temperature anisotropy can be estimated by the system. As a result, electron temperature anisotropy can be measured within the error bar of 10%. In order to search off-axis temperature anisotropy, new collection optics have been implemented. Using four polychromator units, electron temperature at four points in plasma can be measured simultaneously. In this conference, preliminary results by the double-pass multi-point system will be presented.