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HIGH RESOLUTION SPECTROSCOPY OF DITE TOKAMAK IN THE 10Å REGION
J. Dunn, R. Barnsley, K. Evans, N. Peacock
To cite this version:
J. Dunn, R. Barnsley, K. Evans, N. Peacock. HIGH RESOLUTION SPECTROSCOPY OF DITE TOKAMAK IN THE 10Å REGION. Journal de Physique Colloques, 1988, 49 (C1), pp.C1-91-C1-94.
�10.1051/jphyscol:1988118�. �jpa-00227438�
JOURNAL D E PHYSIQUE
Colloque C1, Suppl6ment au n03, Tome 49, Mars 1988
HIGH RESOLUTION SPECTROSCOPY OF DITE TOKAMAK I N THE IOA REGION
J. DUNN, R. BARNSLEY, K.D. EVANS and N.J. PEACOCK'
Dept. of Physics, Leicester University, GB-Leicester LEI 7 R H , Great-Britain
" ~ u l h a m Laboratory, GB-Abingdon OX14 3DB, Oxon, Great-Britain
Abstract:- An account is iven of the X-Ray emission from the DITE tokamak in the spectral region 4~-10% measured by a J o h m curved crystal photographic spectrometer. This high resolution instrument has been used for detailed line identifications eg. of L-shell transitions in the Fe spectrum at wavelengths -8%r and of the He-like ion spectra of Al, Si and Ar. The fine structure has been resolved for H-like Mg, Al and Si. Departures from the statistical value of 0.5 for 6, the intensity ratio of the LF-a doublet, have been observed.
Experimental values for the fine structure separation are presented for these medium Z metals.
Introduction
The results presented here were obtained with a curved crystal spectrometer which uses Johann geometry I l l . The crystal jig and film holder are mounted on high precision rotation stages at opposite ends of a rigid steel tube, which also forms part of the vacuum vessel. This provides good mechanical stability, and allows the crystal to be focused and aligned on the bench prior to mounting to the main chamber. The optical axis is aligned with the source using a flexible bellows, while the main chamber has a combination of angled ports and can be reconfigured relatively easily to cover a range of Bragg angles from 24O to 66"
.
A second bellows provides for radial scans of the DITE Tokamak, though all results shown here are central chord measurements. The crystal radius of curvature can be varied from 0.5m to 5m but is generally set to about 1.3m, and high spectral resolving power of A/&X=5000 to in principle 50000 is possible depending on the choice of crystal. The absolute wavelength calibration, as derived from the alignment procedure and the crystal calibration is typically 1 part in 2000. If lines of known wavelength are present in the spectrum, a relative calibration of about 1 part in 50000 can be achieved. A relatively large waveband(Am)
of about 9% can be covered in a single exposure, as can be seen in Figure 1 which shows n=2 transitions of H- and He-like Silicon, as well as inner shell satellites of Silicon, recorded using an ADP 101 crystal (2d=10.648A). The Si Lyman-a doublet is resolved to 1 part in 2200, the line width being dominated by thermal Doppler broadening.These transitions have been observed in the solar corona [21, and recently with improved resolution in beam-foil experiments 131.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988118
C1-92 JOURNAL DE PHYSIQUE
Wavelength, A
Fig.1 Silicon spectrum recorded using ADP 101 (2dz10.648A)
Survey Spectra
Figure 2 shows a He-like A1 spectrum at around 7.8A, with a He-like Ar spectrum at 4.0A recorded in second order with an ADP crystal, and integrated over 20 DITE shots. This coincidence of monitoring different Z ions in the same waveband could be useful in future experiments. Both of these elements were injected into the plasma for impurity confinement studies.
Figure 3 shows the emission at around 8 . a from Iron L-shell
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~ig.2 shows spectra of He-like Al and second order Ar using ADP 101.
4
Fig.3 L-shell transitions from FeXXIII and FeXXIV. The most intense line is the Mg Lyman-a doublet.
transitions as well as the Mg Ly-a doublet from an ohmically heated Helium plasm with an electron density of 6.0x1013/cm3. The identified Iron lines 141 are mainly from Fe XXIII and Fe XXIV and form almost a continuum of blends, even with a resolution 8X/X of 1 part in 1700.
,
2-12 Magnesium 2113 Aluminium 2-14 Silicon
I\
13-0.57+0.02
Fig.4 Lyman-a doublet for Mg, Al and Si using ADP 101.
Measurement of the Fine Structure Ln a Helium Plasma
Departure from the statistical value of 0.5 for f3, the intensity ratio of the Ly-a doublet, was first observed for Mg in solar flares where the measured value was 0.6 [5] and 0.64 [6]. The solar data has rather poor statistics, which combined with the fact that measured @ varies considerably with any blending of the doublet, m y introduce large errors into the measured
ratio.
The ratio of the Lyman-a doublet, and the fine structure separation have been measured for Mg, Al and Si as shown in Figure 4. The spectrum of Magnesium had the plasma conditions of electron temperature 700eV and electron density 6. OxlO1 The Aluminium spectrum had plasma conditions of electron temperature 700eV and electron density 7.5~10' 3/cm3, with 1MW neutral beam heating. The third spectrum of Silicon was recorded at a lower electron density 2.5x10H/m3 and the electron temperature was estimated at 800_+100 eV from the ratio of the H-like to He-like resonance lines. Electron cyclotron resonance heating ECRH was applied for part of the shot.
Our results for the intensity ratio f3 and fine structure separation are presented below; the predicted fine structure separation is almost constant at 5.41d [7] for Kg, Al and Si.
Element MS Al Si
~eparation,~X(d) 5.7k0.6 5.4k0.1 5.5+0.1 Intensity Ratio,@ 0.56+0.05 0.60k0.02 0.57k0.02
To take account of the blending, we have modelled the lines with gaussians which gave good agreement with the experimental results. We must point out that the measured values for Mg are open to considerable uncertainty due to the possibility of contamination by unresolved Fe lines. This was not a
CI-94 JOURNAL DE PHYSIQUE
problem with either the Al or Si doublet since the waveband could be observed without injecting the element to be studied. The results here show a significant departure from 0.5, though cannot be compared with theory because of no published data on impact excitation by ~ e + + ions.
The measurement of 6 is being continued with Silicon for different plasma densities and without the ECRH. Also, the He-like Silicon intercombination/forbidden line ratio is being studied at different plasma densities. A photoelectric detector is planned for this spectrometer, to give it the time resolution essential for observing the x-ray emission from tokamak plasmas.
References
these proceedings
[ 4 ] Bromage,G.E., Cowan,R.D., Fawcett,B.C., Ridgeley,A., J.Opt.Soc.Am.,68(1)
( 1978
.--
- - ,[51 Grineva,Yu.I., Karev,V.I., Korneev,V.V., et al, Solar Physics, 29,441-446, (1973)
[6] Phillips,K.J.H., Leibacher,J.W., Wolfson,C.J, et al, Astrophys.J.,256, 774-787 (1982)
[7] mohr,P.J., ~t.~at.~ucl.~ables,29(3),453-466 (1983)
