Design of the Photon Recycling Probe Laser for the Divertor Thomson Scattering System in GAMMA 10

A novel configuration of a photon recycling probe laser system for Thomson scattering (TS) system is proposed to measure electron temperature and density of the divertor region in GAMMA10 by using a polarization control multi-pass technique. This configuration can use for simultaneous measurements of the multi-pass TS measurement of the central plasma and the 1 pass measurement of the divertor plasma. To confirm the feasibility of the new method, we have installed double pass TS system in the GAMMA 10 central plasma. As the result, the scattering light intensity at the second pass has maintained more than 95% of first pass signal. By using a same solid angle and a scattering volume of the GAMMA10 central TS system, electron density of 2×10¹⁸ m^-3 will be measured at the divertor region.