K. Sato

M. Goto

T. Kobuchi

National Institute for Fusion Science (NIFS-Repository)

§60. Observation of C VI Charge-Exchange Spectra in LHD Kobuchi, T., (The Graduate University for Advanced Studies), Sato, K., Goto, M. Charge-exchange (CX) process in low energy collisions of C6+ ion with thermal hydrogen atom has been studied during a neutral beam injection (NBI) experiment in LHD plasma. Since the high energy neutral beam for heating doesn't cross the field of view of the spectrometer, the energy of neutral hydrogen which is connected with a CX process is expected to be relatively low (- 10 eV). We present the spectrum intluenced by CX process and discuss on the reacting region of this process. In CX diagnostics, SOXMOS, which is a 2m grazing incidence spectrometer equipped with two multichannel detectors was used. The spectrometer views a horizontally elongated plasma with spatial resolution. Short wavelength side of the detector of this spectrometer was set at wavelength range which covers all the principal I ines of the H- and He-I ike ions of carbon and oxygen. Figure I presents the spectra observed under NBI heating experiment. Most intense spectrum in this region is C VI Ly (( 3.373 nm (I s-2pl. and also the resonance and intercombination spectra. as 0 VII lines at 21.60 and 21.80A, C V lines at 40.26 and 40.73A and 0 VIII line at 18.96A. C VI Ly /1 (ls-3p) line at 28.46A and Ly y (ls-4p) line at 26.99 A are observed. A distinctive feature in the spectral intensity distribution is the same level of the intensities in C VI Ly (3 and Ly y lines. This characteristic mark disappears in the case of very high-density plasma operations. The ratio R1=I(Ly y )/I(Ly (3) calculated by a collisional radiative model of COLRAD on Te=400 keV and lIe= I 013 cm'] is about 0.3. The calculated ratio Ro=I(Ly,9 )/I(Ly a ) is about 0.1. The observed ratio Ro is close to the calculated one. The observed ratio RI is two-three times as great as the calculated one. Obviously, some process to enhance the population of n=4 level of C'i+ is expected. In the case of charge-exchange on fully ionized C ion with thermal atomic hydrogen. electron is mainly captured to quantum number n=4. So. we can conclude that the distincti ve feature in the ratio of C VI Ly y I ine to C VI Ly /3 line is cause'd by the charge-exchange process. In order to investigate the reacting region of 64 charge transfer process between C6+ and H, the spatially resolved measurement for the spectral emission has been tried. Those results are shown in fig 2. The measurements has been achieved for the plasma parameter (stored energy of 400 kJ, averaged electron density of 2-3x 1 019 m-3 and radiation power of 0.5 MW). C VI Ly a radiates as shell structure near the last closed flux surface. At p =0.8, C VI Ly y becomes more intense than Ly (3 . ~ ~ '" co '" <l: l!i l!l 6E3 :> u ;! 6E3 ..; r-M .., :i '> r-'" !! 4E3 0 ; >- r- cri CD,", ~ '" Nr-c;; ~ .. gg Z :lE3 N ~ ~ 5 > ~ » > u 0 uu 0 0 I I 2£3 1E3 zoo 400 600 800 1000 PIXEl NUMBER Figure I: the spectra observed in 1.8-4.2 nm under NBI with H2 pellet injection plasma (# 13402). 40 r-;::J i 30._ >-. ....... (/) ~ 204~ C ...... 10 o I = o 100 200 300 400 500 600 high [lnm] Figure 2: the spatially resolved measurement for the spectral emission. 

Observation of C VI Charge-Exchange Spectra in LHD

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