Validations of calibration-free measurements of electron temperature using double-pass Thomson scattering diagnostics from theoretical and experimental aspects

H Tojo; I Yamada; R Yasuhara; A Ejiri; J Hiratsuka; H Togashi; E Yatsuka; T Hatae; H Funaba; H Hayashi; Y Takase; K Itami

doi:10.1063/1.4961476

Validations of calibration-free measurements of electron temperature using double-pass Thomson scattering diagnostics from theoretical and experimental aspects

Rev Sci Instrum. 2016 Sep;87(9):093502. doi: 10.1063/1.4961476.

Authors

H Tojo¹, I Yamada², R Yasuhara², A Ejiri³, J Hiratsuka¹, H Togashi³, E Yatsuka¹, T Hatae¹, H Funaba², H Hayashi², Y Takase³, K Itami¹

Affiliations

¹ National Institutes for Quantum and Radiological Science and Technology, 801-1 Mukoyama, Naka 311-0193, Japan.
² National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan.
³ Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan.

PMID: 27782603
DOI: 10.1063/1.4961476

Abstract

This paper evaluates the accuracy of electron temperature measurements and relative transmissivities of double-pass Thomson scattering diagnostics. The electron temperature (T_e) is obtained from the ratio of signals from a double-pass scattering system, then relative transmissivities are calculated from the measured T_e and intensity of the signals. How accurate the values are depends on the electron temperature (T_e) and scattering angle (θ), and therefore the accuracy of the values was evaluated experimentally using the Large Helical Device (LHD) and the Tokyo spherical tokamak-2 (TST-2). Analyzing the data from the TST-2 indicates that a high T_e and a large scattering angle (θ) yield accurate values. Indeed, the errors for scattering angle θ = 135° are approximately half of those for θ = 115°. The method of determining the T_e in a wide T_e range spanning over two orders of magnitude (0.01-1.5 keV) was validated using the experimental results of the LHD and TST-2. A simple method to provide relative transmissivities, which include inputs from collection optics, vacuum window, optical fibers, and polychromators, is also presented. The relative errors were less than approximately 10%. Numerical simulations also indicate that the T_e measurements are valid under harsh radiation conditions. This method to obtain T_e can be considered for the design of Thomson scattering systems where there is high-performance plasma that generates harsh radiation environments.