J. Plasma Fusion Res. SERIES, Vol.7 (2006) 40-44

Study of Radiated Spectral Intensities in the HANBIT Plasmafor Plasma Diagnostics
YOSHIKAWA Masayuki, NA Hoon-Kyun1 , SEO Dong-Cheol1 , IWAMAE Atsushi2 , SAWADA Keiji3 ,KOBAYASHI Takayuki, KUBOTA Yuusuke, SAITO Masashi and CHO Teruji
Plasma research center, University of Tsukuba, Tsukuba 305-8577, Japan
1 Korea Basic Science Institute, Yusung, Daejeon 305-806, Korea
2 Faculty of Engineering, Kyoto University, Kyoto 606-8501, Japan
3 Faculty of Engineering, Shinshu University, Nagano 380-8553, Japan（Received: 4 October 2004 / Accepted: 24 May 2005）

Abstract
Intensities of radiation from impurity ions have been studied in the HANBIT plasma for plasma spectroscopic diagnosis using a collisional-radiative model (CR-model). Absolute sensitivity of a vacuum ultraviolet (VUV) spectrometer is obtained using the CR-model for hydrogen. The hydrogen line intensities aremeasured by using the VUV spectrometer and an absolutely calibrated ultraviolet and visible spectrometer.
Therefore, we can study the absolute intensities of the radiation spectra in the wavelength range from vacuum
ultraviolet to visible in the HANBIT plasma. We obtain the neutral hydrogen and carbon ion densities in theHANBIT plasma. Moreover, we measure the electron temperature using the intensity ratio method for plasma
diagnostics.
Keywords:
collisional-radiative model, VUV spectroscopy, UV/V spectroscopy, HANBIT
1．Introduction
In these days, a collisional-radiative model (CRmodel) is an important model for the plasma spectroscopy. The CR-models for hydrogen, carbon andoxygen have been developed [1-7]. The CR-model forhydrogen is normally used for neutral density measurements in many fusion plasma devices [7-8]. However,the comparison between the calculated results using theCR-model for impurity ions and the experimental results must be carried out in many types of plasmas
to construct the model for plasma diagnostics [5-13].
Then, we have studied impurity ion spectral intensities
in the HANBIT plasma at Korea Basic Science Institute, Korea, in order to compare the spectroscopic results with the calculated results using the CR-model for
plasma diagnostics. HANBIT is a suitable plasma device for lower charged ions of CR-model calculations.
We carry out the absolute calibration experiments of avacuum ultraviolet (VUV) spectrometer using the CRmodel for hydrogen. The absolute hydrogen line intensities are measured by using the VUV spectrometer anda 5-channel ultraviolet and visible (UV/V) spectrometer. We study neutral hydrogen and carbon ion intensities for plasma diagnostics using the CR-models in theHANBIT plasma.

2．CR-model calculation
In the CR-model of neutral hydrogen, the population
density of an excited level of principle quantum numberi is given by⎧⎫⎪⎪⎪⎪⎪dn(i) ⎪⎨⎬=⎪Cnn(j)+An(j)⎪jieji⎪⎪⎪⎪dt⎩ ji⎭j>i⎫⎧⎪⎪⎪⎪⎪⎪⎬⎨Cnn(i)+An(i)+S(i)n(i)n−⎪⎪
ijeije⎪⎪⎪⎪⎭⎩ jij<i+ {α1 (i)ne + β1 (i)} ne n1 + γ1 (i)ne nH2 ,(1)where ne and n1 are the electron density and the protondensities, respectively, A ji is the spontaneous transition
probability from level j to level i, C i j is the excitation
or deexcitation rate coeﬃcient by electron impacts fromlevel i to level j, S (i) and α1 (i) are the ionization rate
coeﬃcient by electron impacts and the three-body recombination rate coeﬃcient, respectively, and β (i) andγ (i) are the radiative recombination rate and the dissociative excitation coeﬃcients from molecular hydrogen.
[1-9].
In the CR-model calculation for impurity ions, thepopulation density nz (i) is shown in eq. (2).
C 2006 by The Japan Society of Plasma

Corresponding author’s e-mail: yosikawa@prc.tsukuba.ac.jp

Science and Nuclear Fusion Research40

Study of Radiated Spectral Intensities in the HANBIT Plasma for Plasma Diagnostics⎧⎫⎪⎪⎪⎪⎪dnz (i) ⎪⎨⎬=⎪Cnn(j)+An(j)⎪ji e zji z⎪
⎪
⎪
⎪dt
⎩ ji
⎭
j>i
⎧
⎫
⎪
⎪
⎪
⎪

⎪
⎪
⎨⎬
−⎪
Ci j ne nz (i) +Ai j nz (i)⎪⎪
⎪
⎪
⎪
⎩ ji
⎭
j<i⎫
⎧
⎪
⎪

⎪
⎪⎬
⎨
αz (i, l) +S z (i, k)⎪n (i)n−⎪⎪⎪⎭ z e⎩lk+αz+1 (i, l)nz+1 (l)ne +S z−1 (k, i)nz−1 (k)nel+

Fig. 2 Calculated radiation intensities of carbon ions,CII (a) and CIII (b) when ne = 3 × 1012 cm–3 andTe = 40 eV.

kαz+1CX(l, i)nz+1 (l)ne(2)

lobtained from refs. [4,9]. We compare the line intensity Ii j and the measured spectral intensity in order toobtain the plasma parameters, such as neutral hydrogenor carbon ion densities and the electron temperature.
Figure 1 shows the intensity ratios of hydrogen Balmer and Lyman series lines, Hβ (4d2 D→2p2 P0 , 4861Å)/Hα (3d2 D→ 2p2 P0 , 6563 Å), (a), Hγ(5d2 D→ 2p2 P0 , 4340 Å)/Hα , (b), Lγ (4p2 P0 →1s2 S,972 Å)/Lβ (3p2 P0 →1s2 S, 1025 Å), (c), and Lδ
(5p2 P0 →1s2 S, 949 Å)/Lβ , (d), obtained by CR-model
calculation. Figure 2 shows calculated radiation intensities of carbon ions, C II (a) and C III (b) in ne = 3 × 1012
cm−3 and T e = 40 eV.

Here, nz (i) is the population density of level i of an ionz, ne is electron density, S z (i, k) is ionization rate coeﬃcient from level i of ion z to level k of ion z + 1, αz (i, l)
is electron impact recombination rate coeﬃcient fromlevel i of ion z to level l of ion z − 1, and αz+1CX (l, i)
is charge exchange recombination rate coeﬃcient. The
eﬀective emission rate coeﬃcients εei jf f is shown asεei jf f ≡nz (i)Ai j.
nz (i)ne(3)iThen, the line intensity Ii j from plasma with electrontemperature T e and electron density ne can be given interms of εei jf f asIi j = εei jf f (T e , ne )nz (i)ne .

3．Experimental apparatus
HANBIT device consists of a simple mirror at thecenter with a baseball coil based minimum-B mirror
and a short axisymmetric mirror on each end of thecentral cell. Detailed machine descriptions are givenin refs. [14,15]. The HANBIT device is normally operated with ion cyclotron resonance heating (ICRH) for
plasma production and heating. In these experiments,ICRH power was 60 kW. The typical electron temperature and electron density measured by Langmuir probe
are 40 eV and 2 × 1012 cm−3 , respectively. Figure 3
shows the radial profiles of ne and T e .
A 5-channel UV/V spectrometer consists of collection lenses, a 5-channel 10-m long quarts optical fiber,
and a focal length of 1.33 m Czerny-Turner spectrometer [16]. The detector consists of a 1024 × 256
pixel array (pixel size 26 µm) with a micro-channel
plate (MCP) gated intensifier. The reciprocal linear
dispersion is 0.0085 nm/pixel and the time resolution
is 31 ms/frame. Five optical chords are installed on
the HANBIT central cell for the multi-chord spectroscopy. Total observing range is about 24 cm inthe upper half of the plasma. The UV/V spectrometer is absolutely calibrated by a standard irradiancelamp. Then, we can obtain the absolute intensities of(4)iTransition probabilities, excitation data, ionization, andrecombination rate coeﬃcients in the calculations areFig. 1 Intensity ratios of hydrogen Balmer and Lyman series lines, H¬ /H« , (a), H­ /H« , (b), L­ /L¬ , (c), andL­ /L¬ , (d), calculated using the CR-model.

41

Study of Radiated Spectral Intensities in the HANBIT Plasma for Plasma Diagnostics

Fig. 3 The radial profiles of ne and Te .
Fig. 5 The absolute sensitivity of the VUV spectrometer.

line spectra in the UV/V wavelength range from theHANBIT plasma. A Seya-Namioka type VUV spectrometer is used with an MCP, a phosphor plate and aphotoionization detector. The VUV spectrometer observes the center chord of the plasma. Its reciprocal linear dispersion is 0.058 nm/pixel and the time resolution
is 35 ms/frame.

Lδ /Lβ . Moreover, the absolute intensities of Hα , Hβand Hγ show the population densities n(3), n(4), andn(5) of neutral hydrogen atoms. From the CR-model
calculation, we obtain the relative population densities,n(i)/n(1). Then, we can calculate the population densities of n(1) and n(2). The absolute emissions of Lα , Lβ ,Lγ and Lδ are calculated. We compare the measured intensities of the VUV spectrometer of Lyman lines withthe calculated intensities, in order to obtain the absolutesensitivity of the VUV spectrometer. Figure 5 shows
the absolute sensitivity of the VUV spectrometer. It isalmost constant with the wavelength range from 1000 to1250 Å. However, in the wavelength range from 900 to1000 Å, the sensitivity is changed extremely. The reason of this sensitivity change is not clear. In any case,

4．Spectroscopy in HANBITFirst we measure hydrogen Balmer series line emissions (Hα , Hβ and Hγ ) using the 5-channel UV/V
spectrograph and Lyman series line emissions (Lα (2p2 0P → 1s2 S, 1215 Å), Lβ , Lγ and Lδ ) using theVUV spectrometer, simultaneously. Figure 4 shows thetypical VUV spectrum. By comparing the CR-modelcalculation results of intensity ratios of Hβ /Hα andHγ /Hα , we can calculate intensity ratios of Lγ /Lβ andFig. 6 Radial profile of neutral hydrogen density is obtained using the CR-model calculation.

Fig. 4 Typical VUV spectrum in the HANBIT plasma.

42

Study of Radiated Spectral Intensities in the HANBIT Plasma for Plasma Diagnostics

Fig. 8 Radial density profiles of carbon ions C+ and C2+
are shown in squares and circles, respectively.

3.2 µW cm−2 and about 457 µW cm−2 , respectively.
These are almost comparable to the CR-model calculation results within 30 % of error. This shows that ourcalibration method for VUV spectrometer is useful.
Next, we adopt the intensity ratio method with theCR-model to the plasma diagnostics in order to measure the electron temperature. Intensity ratio method forelectron temperature measurement was used with intensity ratio between C II (2p3 4 S → 2s2p2 4 P, 1010Å) andC II (904 Å) [9]. The intensity ratio is about 7, then theelectron temperature is about 40 eV in the error of 30%. It is compared with the results of the electron temperature measured by the Langmuir probe.

Fig. 7 The UV/V spectra of CII (4267 Å) and CIII (4650 Å)are shown in (a) and (b), respectively.

5．Conclusion
We carry out the absolute calibration experimentsof the VUV spectrometer using the CR-model for hydrogen. The absolute hydrogen line intensities areobserved by using the VUV spectrometer and the 5channel UV/V spectrometer. Then, we prepared thespectroscopic system with the wavelength range fromVUV to visible in HANBIT. The neutral hydrogen andcarbon ion intensities are absolutely observed in orderto obtain the plasma particle densities and electron temperatures using the CR-model. We successfully obtain
the electron temperature using intensity ratio methodwith CR-model.

we can observe the absolute spectral intensities in UV/Vand VUV spectral range in the HANBIT plasma.
By using the CR-model calculation, radial profileof neutral hydrogen density is shown in Fig. 6. Figures 7 (a) and (b) show the UV/V spectra of C II
(2s2 4f2 F→2s2 3d2 D, 4267 Å) and C III (3p 3 P0 → 3s2 S,4647.4 − 4651.5Å), respectively. Figure 8 shows theradial density profiles of carbon ions of C+ and C2+ .
In the HANBIT plasma, the neutral hydrogen density
at the center of the plasma is about 1.2 × 109 cm−3 . C+and C2+ ion densities are about 2 × 107 cm−3 and 5 × 108
cm−3 , respectively. We compare the C II and C III line
intensities in the UV/V spectral range with those in theVUV spectral range. Intensities of C II (4267 Å) and CII (2s2p2 2 P → 2s2 2p 2 P, 904Å) are about 1.0 µW cm−2and about 35 µW cm−2 , respectively. Intensities of C III(4650 Å) and C III (2s2p 1 P → 2s2 1 S, 977Å) are about

Acknowledgements
The authors would like to thank members ofHANBIT group of the Korea Basic Science Institute. This work was supported by JSPS-KOSEF Core-43

Study of Radiated Spectral Intensities in the HANBIT Plasma for Plasma Diagnostics

University Program on Energy Science and Engineering. This work is performed with the support and under the auspices of the NIFS Collaborative Research
Program. This research was partially supported by theMinistry of Education, Science, Sports and Culture,
Grant-in-Aid for Scientific Research on Priority Areas,16082203, 2004.

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