Spectroscopic studies of impurities in the LHD plasmas

Transcription

1 Spectroscopic studies of impurities in the LHD plasmas Visitor: Zhenwei Wu (the institute of plasma physics, CAS -ASIPP) Host: Shigeru Morita (the national institute for fusion science -NIFS)

2 Content 1. VUV spectroscopy cm VUV spectrometer setting-up 1.2 Wavelength calibration and spectral resolution optimization of 20 cm VUV spectrometer 1.3 Typical spectra of 20 cm VUV spectrometer 1.4 Impurity monitor station 1.5 Space-resolved 3 m VUV spectrometer 2. Compact crystal spectrometer 3. Impurity pellet injection 4. Ion heating experiments in the LHD 5. Summary

3 1. VUV spectroscopy cm VUV spectrometer setting-up General information of 20 cm VUV spectrometer: 20 cm normal incidence spectrometer, F/# = 4.5, With a 600 or 1200 grooves/mm concave holographic diffraction grating CCD detector: ANDOR model DO420-BN, Image area: mm2 Active pixels: ch, Pixel size: 26 um/pixel, Read out time: 5 ms.

4 Carbonization of inner wall and inner elements using high pressure carbon liquor before setting-up

5 The feed-through for changing of wavelength, grating and CCD detector

6 Panorama of the 20cm VUV spectrometer

7 1.2 Wavelength calibration and spectral resolution optimization A mercury lamp is used for making this wavelength calibration and spectral resolution optimum as shown in below figure. Because of the concave grating and a planar detector array such as CCD detector we used, The Saggital Focus was applied in detecting system. It can be used to detect effectively the spectra region of the concave grating. So it is very important for the chosen of the incident slit width and the distance of grating to CCD.

8 Mercury lamp for CCD adjustment and λ calibration

9 Line width of spectral line V.S. distance of exit slit to CCD 20 dl0_0a dl0_1849a #101-R 10 0A 1849A #101-R 15 8 Δλ 0 (A) 10 Δλ 1/2 (A) D(mm) D(mm)

10 Line width of spectral line V.S. incident slit width 12 dl0_0a dl0_1849a #110-L 6 dl1/2_0a dl1/2_1849a #110-L 10 5 Δλ 0 (A) 8 6 Δλ 1/2 (A) Incident slit width Δx(μm) Incident slit width Δx(μm)

11 Optimum results After these experiments the optimum results are that the incident slit width is chosen at 60 μm and the distance of 0 Å position to CCD is 1.5 mm for the short wavelength (VUV) region. The performance of spectrometer is mentioned as below. Detectable wavelength region of this spectrometer is from 300 Å to 4000 Å. For short wavelength region (towards 300 Å), the detectable wavelength region is about 700 Å with 0.68 Å/ch averagely for one exposure. For long wavelength region (towards 4000 Å), the detectable wavelength region is about 850 Å with 0.83 Å/ch averagely for one exposure. But for the longer wavelength running, the distance of 0 Å position to CCD needs to be changed in order to focus the image well. The spectral resolution of spectrometer is about 4 Å at wavelength of 1849 Å. Now it is very suitable for measurement of the VUV spectra.

12 The spectrometer installed on LHD

13 The monitor for remote control in the spectroscopic laboratory

14 1.3 Typical spectra of 20 cm VUV spectrometer (i)

15 Typical spectra of 20 cm VUV spectrometer (ii)

16 1.4 Impurity monitor station Five 20cm normal incidence monochromators( å). The 5 VUV monochromators routinely monitors HI (1215 Å), HeI (584 Å), BII (1362 Å), CIII (977 Å), CIV (1550 Å), OV (630 Å), OVI (1032 Å) lines A grazing incidence monochromator (2.2m) Three multichannel 20cm normal incidence spectrometers ( Å) A total radiation monitor A soft-x-ray monitor (< 30 Å) Two multichannel flat field grazing incidence spectrometers (10-500Å).

17 layout and photo of the impurity monitor station

18 1.5 Space-resolved 3 m VUV spectrometer Fig. layout of the 3 m VUV space-resolved spectrometer on LHD

19 Photo of 3 m VUV spectrometer and viewing-angle adjustable mirrors

20 Typical full vertical profiles of impurities (NeVIII 700 Å, ArVIII 770 Å) no vertical asymmetry

21 Emissivity of CV and OV on HT-7 tokamak Vertical asymmetry

22 2. Compact crystal spectrometer Layout and Photo of the crystal spectrometer on LHD

23 Johann-type crystal on the rotary stage and Andor CCD -- model DO420-BN

24 Experimental result of Fe Kα lines and simulation result using a simulation code - Collisional Ionization Equilibrium (CIE) model

25 3. Impurity pellet injection layout and photo of impurity pellet injection on LHD

26 The pellets and Fe Kα lines before and after impurity pellet injection C, Al, Ti and Fe coated C etc. L=0.4-2mm, V= m/s pellet

27 4. Ion heating experiments in the LHD

28 The peaked density profile (ne(0)/<ne> ~ 2.5)

29 Profiles of ion temperature and toroidal rotated velocity from CXRS

30 5. Summary A set of VUV spectrometer with 20 cm focal length has been built-up and installed on LHD apparatus during my stay at NIFS. The VUV spectrum of impurity radiation from LHD plasma was measured successfully from this spectrometer. By using of impurity monitor station, many kinds of impurity line emissions can be observed simultaneously such as HI (1215 Å), HeI (584 Å), BII (1362 Å), CIII (977 Å), CIV (1550 Å), OV (630 Å), OVI (1032 Å) lines. And using a space-resolved 3 m vacuum ultraviolet spectrometer, the vertical profile of impurity line emissions was measured. The results have clearly shown that the vertical profiles have a symmetric feature at upper and lower sides. It is different from the tokamak plasma, in which a vertical asymmetry exists because of the B-curvature drift of impurity ions as seen in HT-7 tokamak. With application of impurity pellet injection and compact crystal spectrometer for the measurement of X-ray spectra from plasma core, the impurity transport of core plasma was studied. A result using a simulation code in collisional ionization equilibrium (CIE) model has been made primarily in the experiment of Fe-coated carbon pellet injection. The ion heating experiment is also carried out in the neon-seeded NBI discharge with carbon pellet injection on LHD. Improvement of the ion transport in the plasma core is expected with the support of a new scenario for confinement improvement in the LHD.

31 Acknowledgment The author would like to thank Prof. Shigeru Morita and all of their colleagues in LHD for their experimental support and very helpful discussions during visit at NIFS.