Experimental Group LHD

K. Ida

S. Kado

Y. Liang

National Institute for Fusion Science (NIFS-Repository)

§11. Measurement of Two Dimensional Electron Temperature Profiles with Hard X-ray CCD Camera on LHD Liang, Y., Ida, K., Kado, S. (Tokyo Univ.), LHD Experimental Group Two-dimensional profiles (38x18 spatial channels) of energy spectra of x-ray emission are measured with the photon counting hard X-ray CCD camera by optimizing the intensity of x-ray with attenuation by Be and AI filters in Large Helical Device (LHD). The hard x-ray CCD camera used in this diagnostic is Princeton Instruments LCX-TEJCCD-1242-ERH/1 with EEV 1242xl152_3ph frame transfer back ilhnnination CCD detector [1-5]. Since half of the pixel is devoted to storage area, the imaging area has 1242x576 pixels. An amount of charge in each pixel of CCD created by the individual x -ray photon is proportional to the energy of x-ray. Therefore, the x-ray energy spectra can be obtained by counting the nwnber of x-ray photons at given intensity (photon counting mode) by choosing appropriate combinations of size of pinholes and thickness of Be and Al filters. The hard x-ray CCD detector is sensitive to the energy range of lOke V to 30ke V. The x-ray energy calibration of the CCD camera was done using various x-ray radio-isotope (RI) sources, such as Mn (5.96keV), Np (13.95keV), Ag (22.1keV) K-a and Ag K-~ (24.95ke V) and L-a (2.9ke V) lines. The slope of the calibration line is 31.6eV/electron (121.5eV/AOC-<:ount). The Fe K-a line is fitted by Gaussian plus linear, and the full width of half maximwn (FWHM) is 72geV at 5.96keV. Although the energy resolution of the hard x-ray CCD camera is too poor to measure impurity lines, it is good enough to derive the electron temperature from the slope of the x-ray energy spectra. The time resolution is determined by the mechanical shutter and it is -lOOms. The spatial resolution of the x-ray CCD camera is determined by the nwnber of wnes divided in the image area (l242x576 pixels). The imaging area of the CCD detector is divided to 684 wnes (38x18), and one wne corresponds to one spatial channel. One energy spectrum is derived by counting the nwnber of photons in one wne (32x32 pixels). Figure 1 shows the two-dimensional profiles of plasma electron temperature derived from energy spectra measured using the hard x-ray CCD camera with 850J.U11 Be and 200J.U11 Al filters for the ECH heated plasma in LHD. The vacuwn magnetic axis is 3.5m and the magnetic field is 2.864T. Twenty reproouced shots are integrated to increase the nwnber of photons and improve the statistics of x-ray photons. The x-ray emission of the plasma with different temperature is integrated along the line of sight This integration effect is larger especially while inner side of the plasma at R<3.5m because the line 154 of sight passes the whole plasma, even at the chord corresponding to the edge. However, the integration effect is relatively small in the outer side of the plasma at 10 3.5m. The electron temperature profiles derived from 2D x-ray energy spectra measured with the tangential hard x-ray CCD camera agree with that measured with Y AG Thomson scattering (TS) for the plasma heated with ECH and NBI, respectively, as shown in Fig. 2. This fact suggests that the energy distribution of electrons is close to the Maxwellian in the energy range of the Y AG and the x-ray CCD measurements. 0 .2 -.. 50 N -0.2 3.2 3 .6 R(m) 4 .0 Fig. 1 Two-dimensional electron temperature profiles measured with the hard x-ray CCD camera in case of the LHD low density ECH heated plasma. 8 r-r-,.-,-....,..,...,.....,~=:T""T7T""':'I--r-t r-r-,.-,-....,..,...,.....,r-r-T"""r""T"""T""""-"-'--' (b) noITB • SX-CCD 3.6 3.8 4.0 4.2 R(m) Fig. 2 Electron temperature radial profiles measured with the hard x-ray CCD camera and the YAG TS in cases of the LHD plasmas heated by (a) ECH and (b) NBI, respectively. References [1] Liang, Y., Ida, K., et aI., : Rev. Sci. Instrum 71, (2000) 3711. [2] Liang, Y., Ida, K., et ai., : Rev. Sci. Instrum 72, (2001) 717. [3] Liang, Y., Ida, K., et al., : IEEE Transactions on Plasma Science Vol. 30,No. 1, (2002) 84. [4] Liang, Y., Ida, K., et al. : Plasma Phys. Control. Fusion 44, (2002) 1383. [5] Liang, Y., Ida, K., et al. : Phys. Plasmas (To be published). 

Measurement of Two Dimensional Electron Temperature Profiles with Hard X-ray CCD Camera on LHD

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