Research and development for the ITER edge Thomson scattering system

Yatsuka, Eiichi; Hatae, Takaki; Itami, Kiyoshi

We proposed a new type beam dump called "chevron beam dump". The key ideas of the chevron beam dump are to reduce the absorbed laser beam energy per unit area and to absorb the beam energy gradually. The laser beam irradiation experiments were carried out to show the validity of this idea. It was confirmed that the absorbed energy density is the correct figure of merit for the laser-induced damage of the beam dump surface. It is expected from the experimental results that the chevron beam dump would have more than times longer life time than conventional beam dumps. We also proposed a new laser beam combiner which combines two separate beams into one collinear and vertically polarized beam. The spinning-half-wave-plate synchronized with laser operation is employed as the laser beam combiner. This type of beam combiner provides robust beam alignment from the laser device to the beam dump.