Very high electron temperature diagnostics using combined Ruby and YAG laser Thomson scattering systems in JT-60U

In recent strong electron heating experiments in JT-60U, it seems that central Te rises above ∼15 keV which is measured by Ruby laser and YAG laser Thomson scattering systems. However, error bars are relatively large (∼100% of Te) and it is difficult to measure the very high Te beyond ∼15 keV with high accuracy because the electron temperature region exceeds that of the original design. To improve the measurement performance in very high Te, we have tried the combination of existing Ruby laser system and YAG laser system. From simulations, it was found that changing the form of the spectrum with the other laser is an effective way for very high Te measurement, furthermore the combined system in YAG laser scattering is well optimized at Te ∼20 keV and relative error is reduced significantly compared with original system. (author)