Description
Thomson scattering systems measure electron temperature under the assumption that the motion of electrons is fully isotropic. However, recently, electron temperature anisotropy has been observed in LHD experiments by spectroscopic diagnostics [1][2]. Thomson scattering diagnostic system is also considered suitable for studying the anisotropy of electron temperature because it directly observes electron motion along a well-defined the scattering vector, which is the difference vector between the incident laser direction and observation direction.
In the original design of LHD Thomson scattering system, it observes backscattered light at a scattering angle of 167 degrees at the LHD plasma center and measures the electron temperature component nearly perpendicular to the magnetic field line [3][4]. In addition, electron temperature component nearly parallel to the magnetic field line can be obtained by using forward scattering configuration. For the double scattering angle measurement, we developed polychromators with nine wavelength channels. The wavelength channels 1-5 and channels 5-9 are optimized for forward scattering and backscattering measurements, respectively. In the 2023 - 2025 LHD campaigns, electron temperature anisotropy has been observed in strong electron cyclotron heating experiments in LHD. We show the experimental setup, calibration and results obtained in the LHD experiments.
This work was supported by NIFS budget (10203010LHD110) and JSPS KAKENHI (JP21H04973 and JP24K07002).
[1] T. Kawate et al., Physica Scripta, Vol.100, 035612 (2025).
[2] T. Kawate et al., Journal of Fusion Energy, Vol.44, 44 (2025).
[3] I. Yamada et al., 40th EPS Conference on Plasma Physics, Proceedings O2.112 (2013).
[4] I. Yamada et al., Journal of Fusion Energy, Vol.44, 54 (2025).