J. Plasma Fusion Res. SERIES, Vol.7 (2006) 1-4Radiation Loss by Impurities Measured from the Large Helical Device
KATO Takako, MURAKAMI Izumi, GOTO Motoshi, MORITA Shigeru,
IDA Katsumi, PETERSON Byron, FUNABA Hisamichi and NAKANO Tomohide1
National Institute for Fusion Science, Toki 509-5292, Japan
1 Japan Atomic Energy Research Institute, Naka 311-0193 Japan（Received: 4 October 2004 / Accepted: 18 August 2005）

Abstract
We have analyzed impurity VUV emission lines quantitatively. Electron temperature is derived from theintensity ratio of C III lines. Radiation loss sources are identified using the spectroscopy and bolometer datain the case of radiation collapse caused by neon gas puﬃng. Time dependent radiation losses by impurity
ions are derived.
Keywords:
VUV spectrum, impurity, radiation loss, Ne VII, C III, O VI
phases; the intensity ratio It (2s2p 3 P − 2p23 P)/Ir(2s2 1 S − 2s2p 1 P) is smaller than unity in an ionizing
plasma and greater than unity in a recombining plasma
as shown in Fig. 1. We compare the calculational results to the spectra measured in LHD for cases wherethe spectra may be classified as ionizing or recombining.
Observed spectra were taken for a plasma heated by
ECH (#15080) and heated by Neutral Beam Injection(NBI) (#28967). In the case of #15080 C III spectra indicate a recombining plasma after ECH power oﬀ. For#28967 case, the carbon spectra always indicate an ionizing plasma despite rapid cooling caused by radiation
collapse. Since NBI is still on after the radiation collapse, low temperature plasma is supposed to be made.
The temperatures are derived from the intensity ratios
as follows; T e 〜40 eV (t = 0.2 − 0.8 sec), T e 〜40 eV→ 20 eV (t = 0.8 − 1.1 sec) T e 〜3 eV (max radiation,t = 1.3 sec), and then T e drops to 2 eV (t = 1.4 − 1.7sec). The waveform of the shot is shown in Fig. 2. Near
the time of radiation collapse (Fig. 2), impurity lineemission increases by more than a factor 4 as shown inFig. 3.

1．Introduction
In low temperature plasmas such as divertor or process plasmas, line emission from impurities is important for plasma diagnostics and plasma modeling. Mostof the radiation losses are caused by VUV emissions
from impurities. Therefore it is important to study VUVspectra quantitatively. Time dependent VUV spectra
were measured in the LHD and are analysed with collisional radiative models for impurities. The Large Helical Device (LHD) is a high temperature laboratory
plasma for fusion research in the National Institute for
Fusion Science.
Time dependent C III, O VI, H Lyα , Ne VII, Ne VI,
Ne V lines were observed in the wavelength ranges ofλ = 90 − 130 nm. We have analysed these spectra using
the collisional radiative models. The radiation loss fromC III, O V, Ne VII and Ne VI ions are obtained fromthe VUV spectra. The time dependent radiation loss
from neon L-shell ions are compared with bolometricmeasurements.
2．C III line intensity ratio
We construct a collisional radiative model (CRM)
for C2+ ions including levels up to n = 5. Our CRM
includes dielectronic recombination to excited states[1,2]. We derived the eﬀective rate coeﬃcients for theintensities of C III lines, Ir (2s2 1 S − 2s2p 1 P, 977 Å)
and It (2s2p3 P − 2p2 3 P, 1175 Å) as functions of electron temperature and density. We study the temperatureand density dependences of the line intensities using ourCRM.
The C III line intensity ratios are substantiallydiﬀerent for the ionizing or recombining plasma

3．Neon ion spectra and radiation loss by impurities at 1 sec
We have analysed the VUV spectra for a NBI
heated (#28967) experiment with neon gas puﬃng
which showed the radiation collapse. We derive theradiation loss rate by impurity ions and comparedthem with the bolometric measurement. The observed
C 2006 by The Japan Society of Plasma

Science and Nuclear Fusion Research

Corresponding author’s e-mail: kato.takako@nifs.ac.jp

1Radiation Loss by Impurities Measured from the Large Helical Device

Fig. 1 Calculated intensity ratio of C2+ lines in ionizing (a) and in recombining plasma (b).

tra and calculations. We find the ion densities of Ne 6+
are about equal to that of Ne5+ .
The absolute neon ion density is derived from charge
exchange spectroscopy (CXS) at t = 1.0 sec. The5249Å line (n = 11 − 10) of Ne9+ is produced by thefollowing charge transfer process with the hydrogen in
the neutral hydrogen heating beam.
Ne10+ + H → Ne9+ (n = 11) + H+ → Ne9+ (n = 10) + hνThe neutral hydrogen heating beam has 140 keV energy. The emission rate coeﬃcient to produce Ne X
5249Å line by charge exchange is calculated by theADAS code [3] as σCX v = 1.0 × 10−8 cm3 s−1 . State- selective charge transfer cross sections to high nlstates are used to calculate the emission rate coeﬃcients. The absolute density of Ne10+ ions is derived
to be N(Ne10+ ) = 2.5 × 1011 cm−3 at the plasma center. We derive the absolute time dependent impurity
radiation loss from the VUV spectra by using the absolute value of the neon ion density. Based on thedensity of Ne10+ , other neon ion densities are calculated for radial distributions by the MIST code [4] ;N(Ne9+ ) = 6.3 × 1010 cm−3 , N(Ne8+ ) = 1.3 × 1011 cm−3 ,N(Ne7+ ) = 3.1 × 1010 cm−3 , N(Ne6+ ) = 3.1 × 1010 cm−3 ,N(Ne5+ ) = 2.5 × 1010 cm−3 at the respective peak positions. The radiation loss rate coeﬃcients of neon
ions by ADAS code are R(Ne9+ ) = 10−26 W cm3 at
1 keV, R(Ne8+ ) = 10−26 W cm3 at 1 keV, R(Ne7+ ) =5 × 10−26 W cm3 at 100 eV, R(Ne6+ ) = 10−25 W cm3 at
100 eV, R(Ne5+ ) = 10−25 W cm3 at 100 eV. Assuming
ne = 1013 cm−3 the radiation loss from the neon Kshell ions is 17 kW m−3 at 1 keV and the neon L-shellions give 72 kW m−3 at 100 eV. This value can be compared with the bolometric measurement 65 kW m−3 at

Fig. 2 The time history of plasma parameters for shot
#28967.

VUV spectra at 1.0, 1.2 and 1.3 sec are shown inFig. 3. We identify the 2s − 2p fine structure transition lines from the neon L-shell ions as second order spectra as shown in Fig. 4 (a); Ne VII (2s2p3PJ − 2p2 3 PJ , 6 lines), Ne VI (2s2 2p 2 PJ − 2s2p2 2 PJ ,3 lines) Ne V (2s2 2p2 3 PJ − 2s2p3 3 DJ , 6 lines), NeIV(2s2 2p3 4 SJ − 2s2 2p4 4 PJ , 3 lines). We calculate theintensities of the Ne VII and VI lines by our collisionalradiative model as shown in Fig. 4 (b). Ion density ratios are derived from comparison of the measured spec-2

Radiation Loss by Impurities Measured from the Large Helical Device

Fig. 3 Observed time dependent VUV spectra.

(a)

(b)

Fig. 4 Observed (a) and theoretical (b) spectra of NeVII and NeVI ions.

ρ = 0.9 for 1 sec in Fig. 5. Here, ρ is the distance fromthe plasma center normalized by the radius of the lastclosed magnetic surface.

4．Time dependent radiation loss by impurities
Since we obtained reasonable values for radiation
loss of neon ions at 1 sec, we try to study the time
variation of radiation loss by impurities using the time3

Radiation Loss by Impurities Measured from the Large Helical Device

Fig. 5 Radial emission profile measured by bolometer.
Fig. 6 Time dependent radiation loss from impurity ions.

dependent spectra. From the observed intensity of Ne
VII 2s2p 3 P − 2p2 3 P at around 500 Å, the absolute intensities of other ions are estimated. With N(Ne6+ ) =3 × 1010 cm−3 , ne = 1013 cm−3 and eﬀective excitation rate coeﬃcients, C e f f (561 Å) = 2 × 10−9 andCe f f (564 Å) = 7×10−10 cm3 s−1 , absolute observed volume emissivities are obtained to be I(561 Å) = 6 × 1014
−1photons cm−3 s and I(564 Å) = 2 × 1014 photons
cm−3 s−1 . The observed photon counts for Ne VII 561 Åand for Ne VII 564 Å at t = 1 sec are 2260 and 633
counts, respectively. From the C III 977.0 Å(2s2 1 S−2s2p 1 P) observed photon counts 1395 at t = 1 sec, theabsolute volume emissivity I(C III977 Å) = 4.6 × 1014
photons cm−3 s−1 is derived using the intensity of neonemission lines. With C e f f (977 Å) = 6 × 10−8 cm3 s−1
and ne = 1013 cm−3 , density of C2+ ions N(C2+ ) =7.6 × 108 cm−3 is obtained assuming the radial widthof C2+ is the same as Ne6+ . From our collisional radiative model, the radiation loss from C2+ is obtained
to be 0.8 kW m−3 and radiation loss of carbon L shellions is 2.3 kW m−3 . Based on the radiation loss att = 1 sec, the time dependent radiation loss for C2+ isderived from time variation of the VUV line intensity.
From the O VI 1031 Å(2s 2 S − 2p 2 P) observed intensity at t = 1.0 sec, absolute volume emissivity I (O VI1031 Å) = 6.6 × 1014 photons cm−3 s−1 is derived. With
Ce f f (1031 Å) = 1.3 × 10−8 cm3 s−1 and ne = 1013 cm−3
the density of O5+ ions, N(O5+ ) = 7.7 × 109 cm−3 is obtained. Radiation loss of 8 kW m−3 from O5+ is derived.
Radiation loss from the L-shell ions is estimated to be
16 kW m−3 . Based on the absolute values at 1 sec, weestimate the time dependent radiation loss of diﬀerent
ions using the time dependent line intensities as shownin Fig. 6. The radiation loss by Ne VII and Ne VI lines
is 250 kW m−3 at 1.3 sec and this compares well withthe bolometric measurement 320 kW m−3 within 30 %.

5．Summary
We analyzed the impurity spectral emission quantitatively. Electron temperature is derived from the intensity ratio of the C III line intensities. Radiation loss
sources are identified using spectroscopy and bolometry in the case of radiation collapse caused by neon gas
puﬃng. Time dependent radiation loss of impurity ionsare derived from line intensities of impurities. Due tothe large radiation loss by neon L-shell ions, temperature falls starting from the periphery leading eventuallyto the radiation collapse. After the radiation collapse,
low charged carbon ions are the dominant source of radiation. We need more precise measurements for the radial distribution of electron densities and temperatures
as well as line intensities, especially in the periphery
region where the radiation loss is dominant. It is notedthat reliable and comprehensive atomic data are important for such plasma diagnostics.

[1]

[2]

[3]
[4]

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