J. Plasma Fusion Res. SERIES, Vol. 3 (2000) 402406

lmpurity lon Diagnostics in the GAMMA 10 Tandem Mirror
YOSHIKAWA Masayuki*, OKAMOTO Yuuji, KAWAMORI Eiichiro, ITO Takahiro, WATABE Chikara,
WATANABE YoshihiKo. IKEDA Katsunoril. YAMAGUCHI Naohiro2,
TAMANO Teruo and YATSU Kiyoshi
Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577, JapantNational InstituteFusion Science, Toki, Gifu 509-5952, Japanfor2Toyota Technological Institute, Tempaku, Nagoya 468-8511, Japan(Received: 18 January 2000 / Accepted: 18 April 2000)

Abstract
We constructed some spectroscopic measurement systems that cover the wavelength range from soft

X-ray (SX) to visible lights. We have observed the absolute impurity line intensities, Doppler line
broadenings, Doppler shifts by ultraviolet and visible spectrograph and time dependent radial profiles of

the impurity lines by the vacuum ultraviolet (VUV) and the SX spectrographs. We determined theradiation loss in the wavelength range from visible to VUV and carbon ion density. These spectroscopicsystems could be powerful tools to diagnose the GAMMA 10 plasma in a long pulse operation.

Keywords:
spectroscopy, UV/V spectrograph, VUV spectrograph, SX spectrograph, GAMMA l0 tandem mirror

1. Introduction

wavelength range from SX to visible lights. In order toobtain impurity ion temperatures, we used the UV/V
spectrograph and measure Doppler broadenings of theImpurity lines and continuum radiation in thewavelength range from visible light to soft X-ray (SX)

are emitted from fusion plasmas. These emissions
provide us information about radiation power losses, ion

impurity spectral lines. Radial electrostatic potential

density profiles which directly relate to the impurity

transport in magnetically confined plasmas andof variously charged impurity ions. In order to measuretime dependent impurity ion profiles in the radialphenomena related to potential formation in the radial

direction, the VUV and the SX spectrographs were used.

direction. We prepared two 2-dimensional ultraviolet
and visible (UV/V) spectrograph systems (2000-5000
A) tt-:l, time- and space-resolving vacuum ultraviolet(vUV) (ls0-1050 b V-tj and SX (20-3s0 A)

Impurity ion densities have been estimated by using acollisional radiative model (CR-model) calculation code
which is provided by T. Kato [0]. We obtained
radiation loss in the wavelength range from visible tospectrographs [7-9] for impurity diagnostics. TheseVUV and the carbon ion density by using these

spectroscopic measurement systems can provide

spectroscopic measurements.

profiles have been obtained by measuring Doppler shifts

simultaneous spectral, temporal and spatial resolution of
the plasma radiation. Spectroscopic data taken by these

2. Spectroscopic Diagnostic Systems
The two space-resolving UV/V spectrographdiagnostic systems would be important for long pulse
operation of the fusion plasma research.
We have measured the absolute intensities ofsystems view the plasma colurnn vertically. Figure I
shows the schematic of the UV/V spectrograph. The

emitted spectral lines of radial distribution in theCorresponding author's e-mail: yosikawa@ prc.tsukuba.ac.jp402@2000 by The Japan Society of Plasma
Science and Nuclear Fusion ResearchYoshikawa M. et al., lmpuity Ion Diagnostics in the GAMMA 10 Tandem Mirror

20 rlcml

ILenses,f0 ch Optical Fiber
STU400E-S x 40

Aberration corrected concave grating

f=350mmx2

Plasma ii

950 mmto CCD camera?,0GAMMATO

X

Plasman Czerny-Tumer Spectrometer01m0\ilavelength I A ]Fig. 1 Schematic of UV/r' spectrograph system.

Fig. 2 Schematic of VUV spectrograph.

UV/V light from the plasma is collected by a quartz lens
Aberration corrected concavdgrating

and then transferred to a spectrometer through an 8-mlong and 40 channels ofbundled optical fiber anay. The
spectrograph covers the plasma radially from x = -20
cm to x = 20 cm. The observable wavelength of thespectrograph is in the range of 2000 A to 5000 A. ttre
image of the exit plane of the spectrograph is focused
onto an image intensifier tube (Hamamatsu V4435U)
coupled with the CCD camera (Sony TK-66 for central

cell system and XC-75 for anchor cell system). The
frame rate of the CCD camera is 30 frame/s and theGAMMAlO

shutter speed is 10 ms. The two UV/V spectrographsystems are absolutely calibrated by using a tungsten
ribbon filament standard lump.
The VUV spectrograph (Fig. 2) can provide spatialand spectral distributions of plasma radiation in thewavelength range 150-1050 A. It consists of an entrance
slit of limited height (100 pm x 6 mm), an aberrationcorrected concave grating with varied spacing grooves(Hitachi P/N001-0464), and an image-intensified two-Plasma

50

3s0

Wavelength I A ]Fig. 3 Schematic of SX spectrograph.

size,256 x 256 pixels, can be varied from 4 to 106
frame/s. Absolute calibration experiments for thesespectrographs have been performed on the overallsensitivities for the covered wavelength by using

dimensional detector system. One can observe the upper
half of the plasma with a field of view of about 25-cm
diameter. The SX spectrograph system (Fig. 3) is thesame as the VUV spectrograph in the optical system ofspatial imaging. The grating (Hitachi PA{ 001-0266) isdesigned to cover the 20-350 A wavelength range. This
spectrograph also settled on the GAMMA l0 so as toobserve the upper half of a plasma about 20 cm in radial
direction. The detector systems of both the VUV and theSX spectrograph consist of microchannel-plates (MCP)
intensified image detector assemblies (Hamamatsu

synchrotron radiation at the Photon Factory in the HighEnergy Accelerator Research Organization [6,9].

3. Spectroscopic Measurements in theGAMMA 10
The GAMMA l0 is a 27m long tandem mirror
consisting of a 5.6 m long axisymmetric central cell,
two anchor cells for suppressing MHD instability andaxisymmetric end mirrors for forming plug/barrier
potentials. Plasmas in the central cell are produced andheated by ICRH with hydrogen gas puffing and the plugpotentials are produced by ECRH. The typical plasma

F2814-23P,50 x 50 mm2) and image recording cameras(Reticon MC9256) with fast scanning controllers (CCDRS9l00). The frame rate of the cameras with full image
403

Yoshikawa M. et al., Impurity Ion Diagnostics in the GAMMA l0 Tandem Mirror

parameters in the central cell are as follows; the electron

similar plasma. Therefore these measurements aredensity is 2 x l0r2 cm-3, the electron temperature is 80
eV and the ion temperature is 5 keV. The maximum
plasma duration is 0.5 sec and the maximum duration ofpotential formation is reached to 0.15 sec. The two UV/
V spectrographs are settled on the central cell and theanchor cell. The VUV and the SX spectrographs are seton the central cell and the barrier cell, respectively.
Some examples of measured spectra by using these
spectrographs are shown in Fig. 4. Figures 4 (a) and (b)show the spectra of OV (278-279 nm) lines measured
by the UV/V spectrographs in the central cell and theanchor cell, respectively. Figures 4 (c) and (d) show theVUV spectrum in the central cell and the SX spectrum
in the barrier cell, respectively.

consistent each other.

We compared the CII line (904 A; intensity
measured by the VUV spectrograph to that from CR-(c)(a)

ela 4lt

J*
6es

I l!? nQ tt tol2

rlInE
7770

5@

tr

to9t (b)00lo-a 4x l0t(d)P,IIn the GAMMA 10 central cell region the absolute

2770

21aO

27q ^]

4m
4mo50tets2m503@39

Wavelength I A ]emission intensities were measured along radial
direction by the UV/V and VUV spectrographs. The
total emission intensity of various ions line spectrumS;
6O{lWavelengh [A]Fig.4 (a) and (b) show the spectrum of OV lines
measured by UV/V spectrograph in the central celland the anchor cell. respectively. (c) shows VUVspectrum in the central cell and (d) shows the SX
spectrum in the barrier cell.

and continuum spectrum throughout the UV/V andVUV regions were integrated over plasma cross section
and plasma volume. The total power of emitted
spectrum obtained from the above procedure wasdetermined to be less than I kW, which can be thoughtas the radiation loss in the central cell. This power
corresponds tobe 0.5Vo of the total heating power of theGAMMA 10. Therefore the radiation loss is not a severe
problem in the GAMMA 10.

oo-El<ESThe Doppler broadening measurements by using
the UV/V spectrographs showed that the OV ion
temperature was about 0.4 keV in the central cell and 7keV in the anchor cell (Fig. 4 (a) and (b)). Thissignificant difference in the OV ion temperature isEAtE ns

thought to come from the following reason. The
cyclotron frequency of Oa* ion in the anchor cell isOtr!,t0o.e5

equal to a"i/4, where al"1 corresponds to the fundamental.)

cyclotron frequency ofhydrogen ions. The frequency offundamental ICRH waves is equal to oci in the anchorcell. The Oa'ions could be heated due to cyclotron
higher harmonic heating [].

Radial profiles of the electrostatic potential also
obtained by using the UV/V spectrograph [2,3]. Figure 5€ 5oo!lshows the typical results of electrostatic potentials
obtained by using plasma rotation measurements in theE x B rotation dominant plasma, Fig. 5 (a) shows theelectron density, Fig. 5 (b) and (c) show the impurity

0-o.2 -0.1

00.1

0.2

Radius I m ]density and the electrostatic potential profiles,respectively. The potential difference between the centerand the edge is 0.9 kV. The beam probe measurement

Fig.5 (a) shows the electron density, (b) and (c) show
the impurity density and the electrostatic potential
profiles, respectively.

provided the l-1.2 kV of potential difference in the404

Yoshikawa M. er al., Impurity Ion Diagnostics in the GAMMA 10 Tandem Mirror
3.5 10I

3 l0-8o<;.x=U

2.5 t0{2 lo'E
1.5 l04I lo{
5 l0'e010'I

l0100

1000

A tevlFig.6 CRM calculation results about Cll line (904 A)
intensity.

model calculation in order to obtain the total C+ iondensity. Figure 6 shows the calculated emissivity of CIIline (904 A). fne CII line absolute emissivity was
obtained by a procedure described before [6]. Theplasma density and the electron temperature were(d) 149-169 mswith ECRIIomeasured by microwave interferometer and SX510

measurement, respectively. Then we can calculate theC+ ion density using CR-model calculation. The C+ ion
density of the plasma center is about 2 x 107 cm-3. It is
comparable to the result obtained by the same procedureof calculation of CII line (4267 L) measured by the UV/

t6(e) 209-229 msaV spectrograph.

Radius I mm ]Time dependent C ion radial profiles in the 0.2-seclong plasma measured by the VUV spectrograph are
shown in Fig. 7. From the results of this C ion behavior,
we could make a scenario of impurity transport in theGAMMA l0 tandem mirror. First, the impurities are

Fig. 7 Time dependent C ion radial profiles in the 0.2-sec
long plasma measured by VUV spectrograph.

impurity line intensities, Doppler line broadenings,
Doppler shifts by UV/V spectrograph and timedependent radial profiles of the impurity lines by theVUV and the SX spectrographs in the GAMMA 10. We
obtained radiation loss in the wavelength range fromvisible to VUV in the GAMMA l0 central cell.

sputtered from the vacuum vessel wall by the electron
impact and the charge exchange neutral particle impact
and enter into the plasma during the plasma production
and buildup phases. Next, the impurities are ionized by
the electron impact and the ion impact. As the plasma

grows, the charged states of impurity ions areprogressing, and the peak position of impurity ions ofMoreover we obtained Ct ion density in the central cell.
These spectroscopic systems could be powerful tools todiagnose the GAMMA l0 plasma in a long pulse

each ionized state moves towards the outer region.
When the ECRH power is injected into the plug/barrier
region, the plug potential is maintained. Then, the ions,hydrogen ions and impurity ions, are axially confined by
the plug potential. After ECRH ceases, the impurity ion
peaks appear in the same region as that before ECRH isoperation.

Acknowledgments
We would like to thank the GAMMA l0 group for
their operational and diagnostic support and for useful
discussions. This work was supported by a grant-in-aidfor Scientific Research from the Ministry of Education,
Science, Sports and Culture, Japan. Part of this work
was performed under the approval of the Photon Factory
Advisory Committee.

on.

4. Gonclusion
We constructed the absolutely calibrated
spectroscopic measurement systems in the wavelength

range from SX to visible lights. We observed the405

Yoshikawa M. er c/., Impurity Ion Diagnostics in the GAMMA l0 Tandem Mirror[7] M. Yoshikawa et al., J. Synchrotron Rad. 5, 762

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