J. Plasma Fusion Res. SERIES, Vol.5 (2002) 342-345

Behavior of Intrinsic and Injected lmpurities in Heliotron J
ECH Plasmas
KAWAZOME Hayato, MAENO Shogo, KONDO Katsumi, IRIGUCHI Masao, TAKEDA Masafumi,
MIZUUCHI Tohrur, OKADA Hiroyukir, NAGASAKI Kazunobur, SANO Fumimichir, BESSHoU Sakae,
MANABE Yoshito, SHIDARA Hiroyuki, ANG Wan Leng, TAKAMIYA Tasho, TSURU Hiroki,
TOMIYAMA Keishi, OHNO Yoshinori, KUBO Hiroyasu, NISHIOKA Yusuke,YUKIMOTO Hidetoshi and OBIKI Tokuhiror
Graduate School of Energy Science, Kyoto University, Gokasho, Uji 611-0011, Japan
I Institute of Advanced Energy, Kyoto [Jniversity, Gokasho, {Jji 6Il-0011, Japan(Received: 1l December 2OOl / Accepted: 15 July 2OO2)

Abstract
The behavior of impurities is studied for Heliotron J ECH plasmas using VUV and visible
spectrometers. Plasmas are produced by 70 GHz ECH. In VUV spectra, oxygen (O III, O ry, O VI),
carbon (C III, C IV), titanium (Ti XI, Ti XID, iron (Fe XV, Fe XVI) and chromium (Cr XIII, Cr XIV) areidentified as typical impurities. For impurity injection experiments, movable gas puff system is installedin Heliotron J. Preliminary spectroscopic results of helium gas injection into the plasma are presented.

Keywords:
Heliotron J, impurity behavior, VUV spectra, impurity injection

1. Introduction
In a study of magnetically confined plasma,system with focused incident beam is installed.

In this paper, the behavior of intrinsic and injected
impurities are investigated for Heliotron J ECH plasmas
using VUV and visible monochromators. Thespectrometers are viewing the center of plasma and used
to identify impurities and temporally resolved spectral
intensity emitting from VUV and visible wavelength
region. The identified typical impurities in Heliotron J
ECH plasmas will be described in Sec. 2. Section 3
describes the preliminary spectroscopic results of helium
injection into the plasma by the movable gas puff

generating high temperature plasma is one of the main
issues. Impurities in a fusion plasma play a crucial role

through radiation losses and the dilution of fuel. It is
important to understand the intrinsic impurity species
and their behavior. Also it is important to study impurity

transport and impurity control with injection
experiments.

Heliotron J is a medium sized helical-axis heliotron

device with Z = L and M = 4 [1,2]. The various
magnetic configurations can be formed for the study ofparticle and impurity control, i.e. helical divertor andisland divertor configuration [3]. In previous study,hydrogen plasmas are produced by 53 GHz ECH with
the injected power of 4OO kW in the magnetic fieldstrength from 0.85 T < B < 1.35 T and two effective

system. The last section gives summaries.

2. Behavior of Intrinsic lmpurities in aHeliotron J ECH Plasma
Behavior of intrinsic impurity species in Heliotron
J ECH plasmas is studied. VUV spectra are measured

heating regions are observed [4]. Recently 70 GHz ECH@20O2 by The Japan Society of Plasma

Corresponding author's e-mnil: kawazome @ center.iae.lcyoto-u.ac.jp
342

Science and Nuclear Fusion Research

Kawazome H. et al., Behavior of Intrinsic and Iniected Impurities in Heliotron J ECH Plasmas
Shot No. 05302

400il"(a)

Te800

1.2 Fli zoo^t3 700

0.6 ,6160 180O).j.. ........ i ...

E ooo

itil

E

gs0'E 0.04

900-9 500

0.0.n'

280 300

200ilitt lr.

-_r" r-- _ l--_F 400- 300[oV(278.1 nm)

Ill200A100

Y o.ozwavelength(m)0.00

160 180.2 s.o200

220240(c)260280Fig. 2 VUV spectra at t = 215 ms in shot No. 5302. ldenti-300

fied spectra are indicated by their species andwavelength in nm.

IIa

€ 2.o
E 1.0---r-Fe XVI (33.54 nm)--+- Cr XIV (38.98 nm)

oE 0.0160---+-O m (34.53 Dm)

180 200 220 240 260 280 300-5- CW(31.24nm)

Time (ms)1 300

Fig. 1 The temporal evolution of the discharge in standard configuration (B= 1.28Tl,. The plasma is produced by the 70 GHz ECH: (a) the line average
electron density and the electron temperature, (b)line intensity of O V (278.1 nm), (c) line intensity

h'E
200
aof Ho.
100

with using a time-resolving grazing incident
spectrometer with a multichannel detector [5].

60Wavelengths o1'observed spectra are ranged from 15 nm
to 40 nm, the nrinimum time resolution is 10 ms and thewavelength resolution is approximately 0.1 nm.
Plasmas ale produced by the 70 GHz ECH with thepower of 400 kW and the pulse width is 80 ms. Figure I
shows a temporal evolution of the discharge in standard
configuration (B = 1.28 T). The line average electronTime (ms)Fig. 3 Time-resolved line intensity in shot No. 5302.

XVI and Cr XIV, increase of the charge state population
causes increase in the intensities. After 230 ms, all line

density and the electron temperature are evaluated fromintensities decrease with density decrease. In this phase,the electron temperature is almost constant. So it isexpected that the electron density decreases withkeeping its profile. As the typical intrinsic impurity,oxygen (O III, O IV, O V, O VI), carbon (C III, C IV),titanium (Ti XI, Ti XII), iron (Fe XV, Fe XVI) andchromium (Cr XIII, Cr XIV) are identified. Table I
shows the identified spectra in Heliotron J ECH

a microwave interferometer and a soft x-ray filter
absorption melhod, respectively. The electron density
and the electron temperature are almost constant from210 ms to 240 ms. Figure 2 shows VUV spectra at t =215 ms. Figure 3 shows time-resolved plot of Fe XVI(33.54 nm), Cr XIV (38.98 nm), O nI (34.53 nm) and C
lY (31.24 nm) line intensities in the same discharge.
The spectromeler has not been absolutely calibrated andFig. 3 shows only time evolution of the individual line

plasmas.

intensity. These intensities are peak values bysubtracting the background. In Fig. 3, O III and C IV

3. Helium Gas Iniection
In this section we present some preliminarylines are obsen'ed at 185 ms and the intensities increase
because of ionization phase. For metallic impurities, Fe

spectroscopic results ofhelium injection experiment. To

investigate the effect of the edge plasma on the impurity
343

Kawazome H. et aI., Behavior of Intrinsic and Injected Impurities in Heliotron J ECH Plasmas

Table 1 ldentified typical intrinsic spectra in the Heliotron J ECH plasmas.
Wavelength (nm)Transition

Species17.22

OV

2s2 1 So2s3p Pi

18.39

ovl

2p'Pi,,

3s'5,,,

19.30

2s2p3Pi2s2p3Pi2s3d3D"2s3s 3S,

22.04OV
OV
OV

23.86

2s3d 1D,
2s23d2Dv

21.52

1olv

2s2p 1Pi
2s22p2Pi,,

28.42

Fe XV

3s"So

3s3p1 Pi

29.99

2s2p2 2P*

31.24

olv
clv

2s25,,,

2s2p(3P'l3d 2P&,
3p"P&,

32.83

Cr Xlll3s"So

3s3p1Pi

33.54

Fe XVI

3s25,,,3p'Pi,,

34.53

o lll

2s22f 1So

2s'?2p3d 1Pi

36.06
36.08

cill

2s2p3Pi
3s'S,,,

2p3p3PoFe XVI

36.72

otv

2s2p2 2Po,2s2p(3P"l3s2P&2

37.40

o lll

2s2p23P,

2s22p3s3Pi

38.41

ctv

2p'P3,,

3d'4,,38.61

Ti XI

3s"So

3s3p1Pi

38.62

cill

2s2 1So2s3p1 Pi

38.98

Cr XIV

3s2Sr,,3p"P&,

3p'Pi,,

3 x l0r7 m-3, respectively. Injection of helium gas causes
increase in the electron density from 1.4 1gt8 *-3 1openetration into the core region and the influence of thepenetrated impurity on plasma performance, a movablegas puff system is installed in Heliotron J. The distance
between the top of nozzle and the last closed magnetic
flux ICMD can be varied. The nozzle is set toward themagnetic axis.
Plasmas are produced by the 70 GHz ECH in thestandard configuration (B = 1.26 T). The pulse widtht

2.7 x l}ts m-3 and decrease in the electron temperaturefrom 0.75 keV to 0.45 keV.
Figure 5 shows time-resolved line intensity of Fe
XVI (33.54 nm), Fe Xy (28.42 nm) and O III (34.53nm). After helium gas was injected, intensities increase

with increasing the electron density. The electron
density and Fe XVI, Fe XV and O III intensities
increase 1.9 times, 2.2 times,6 times and 1.6 times,respectively. O III ions present in the cooler edge region

and the injected power are 100 ms and 400 kW,respectively. To observe the influence of injected
impurity, a low density plasma is produced. The nozzle
is located at 60 mm outside the LCMF. Figure 4 showsa temporal evolution of the line average electrondensity, the electron temperature, and He I and He II
intensities in the helium gas injected discharge. The
helium gas is injected at 233 ms and twned off at 244
ms. He I and He II line intensities are measured by two
monochromators viewing top of nozzle and located at
45 degrees in the toroidal direction from the port ofhelium injection, respectively. He I and He II line
intensities quickly peak in l0 ms after helium is injected
and then decays exponentially as a result of further
ionization and particle loss. The estimated ionization
time from He I to He II in this case is 0.42 ms. The
electron temperature and density of the edge region,
which are measured with movable probe, are 30 eV andand decrease of electron temperature dose not affect its

ionization balance. On the other hand, with decreasing

the electron temperature, the recombination andionization rates of Fe XVI ions, which are present in thecore region, increases and decreases, respectively.
According to the ionization balance, Fe XVII exists

before helium gas injection. It is not confirmed
experimentally because of the wavelength of Fe XVII
resonance line is shorter than the available wavelength

region of the spectrometer. When the electrontemperature decreases, Fe XVII and Fe XVI recombineand Fe XV becomes the most abundant ion. In thisdischarge, decay time of the He II line intensity is aboutl3 ms.
To investigate the relation between the behavior of344

Kawazome H. et al., Behavior of Intrinsic and Iniected Impurities in Heliotron J ECH plasmas
ShotNo. 05868["^8-oa(a)600l;4000160
1200oE 2oo^{, 800
fl 4000160 180 200 220 240 260 280 300

OLTime (ms)160

1.2-Fig. 5 Time-resolved line intensity with helium gas injecHe I (587.60.8nm)

iltion (#05868).

t.,>' o.4e0.0 ul160
34. Summary
200He II (468.6240280nm) lt

The study of impurity behavior in Heliotron J ECH
plasmas has been started with spectroscopic methods.

320

For ECH plasmas, typical impurity species identified byVUV spectra are oxygen, carbon, iron, chromium and(d)titanium. It is considered that these impurities arereleased from the vacuum vessel wall by desorption andhsputtering processes.
o0E*
160200240

Time (ms)280

In impurity injection experiments, helium gas isinjected by movable gas puff system. Helium decay time
is obtained as about 13 ms from He II line. In electron
density scan, the particle number of ions penetrated into
core plasma depends on the electron density. It seems
the screening effect due to electron collisional ionization
at the edge region.

320

Fig. 4 The temporal evolution of the discharge with helium gas injection: (a) the line average electron
density, (b) the electron temperature, (c) line intensity of He | (587.6 nm), (d) line intensity of He ll(468.6 nm).

References

tll M. Wakatani et a/., Nucl. Fusion 40, 560 (2000).
injected impurity and plasma conditions, we perfonned
electron densit.y scan (0.17 x l0re m-3 < n. < 2.2 x l}\em-3; in standard configuration. The dependence of decay
time of He I rnd He II line intensity is not observed12) T. Obiki er a/., Plasma Phys. Control. Fusion 4,clearly. On the other hand He II line intensity[4] T. Obiki et a/., Nucl. Fusion 41, 883 (2001).
t5l K. Kondo et al., Jpn. J. Appl. Phys.27,2368

l15l (2000).

[3] T. Mizuuchi et al., J. Nucl. Mater.290-293,678682 (2001).

normalized by the electron density, which indicates the(l988).

particle numbcr of helium ions penetrated into the coreplasma region, increases with decreasing the electrondensity. We guess this result arises from the screening
effect due to electron collisional ionization at the edee
region.

345