A. Matsubara

E. Ishiguro

K. Sato

Yin Win Kyawt

Yiyuan Gong

National Institute for Fusion Science (NIFS-Repository)

§ 24. Diagnostic of LHD Using a Space andTime Resolving Soft X-ray PolychromatorThe previous method for the optical alignment of thepolychromator was based on the idea that the positions ofthe entrance slit and the grating were precisely given onmanufacture. Instead of this, a new method for alignmentE E,--...c c....... 00C('i') C\J00 00::J 0 0..c 15 N.tf« ¥..........,«.......enc 10Q.).......C5was developed. The incident direction of the light wasdetermined by using two pinholes, and then the grating wasplaced so as to be tangential to the incident direction.As a result, a high resolving power of 1000 was achieved atAl-k a line, and the difference of the focusing distancefrom the Rowland circle was within 10 mm. Figure 1 showsthe high resolution spectrum of Al-k a line.The electron temperature at the center of LHD plasmamay be over 4 keV. Then Fe and Ti atoms, the main metalimpurities in LHD, can be highly ionized as He-like orH-like. By identification of 2s-3p transitions, the He-like andH-like ions of the metal impurities can be qualitativelymeasured with the soft X-ray polychromator which covers aspectral range of 0.7-3 nm. For Fe impurity, 21-31' transitionsin F-like and Li-like ions may be also detected. Our researchis expected to provide basic data on transport mechanism byimpurities at the plasma core.Optical alignment of the soft X-ray polychromator hadbeen performed using a characteristic X-ray from Aluminumatom(AI-K a, 0.834nm) as a light source up to 2001. Theresolving power obtained for a 10 fJ m slit width wasapproximately 520 which was a third of the theoretical value1500. In addition, the focusing distance from the grating was100 mm larger than the theoretical one. This meant that thebest focusing position of the image was always out of theRowland circle.Ishiguro, E., Gong Yiyuan, Kyawt Yin Win (Univ. ofthe Ryukyus)Matsubara, A., Sato, K.The result above suggested that it was necessary tocheck the radius of curvature of the spherical grating used inthe polychromator. A Foucault's test for the grating wasdone by using an optical bench 12m long in 2002. Themeasured value for the radius of curvature of the grating was10096.9±9.2 mm, while the value given by a maker was10331 mm. A difference 234mm for the radius of curvatureFig. 1 Observed Al -K a line.was found but could not explain the low resolving powerand the discrepancy of the detector position from theRowland circle.173

Diagnostic of LHD Using a Space and Time Resolving Soft X-ray Polychromator

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)