1 - Nuclear Sciences and Applications - IAEA

45
2 30
a.
" 15
0
7 e s
9 2.5 :
ic o
~ 10
"f o
-10
IAEA-CN-50/E-III-2
80 120
t(s)
= 0B3m
160 200
FIG. 2. Oscillograms of longest duration discharge. The injected RF power was less than 20 kW.
was kept at about 2.4 X 10 12 cm" 3 . If the working gas is fed constantly without control,
the Ha line intensity increases gradually with time by the recycling process as
shown by the dashed line. Although the resulting density increases up to about 4 x
10 n cm" 3 , the plasma current decreases gradually with increasing density and
finally even fades out. By this gas feed control, we obtained reproducible, long duration
discharges and performed stable operations of more than three minutes. The
duration was limited by the time permissible for continuous operation of the power
supply for the vertical field coil.
Figure 2 shows the discharge waveforms with a maximum duration of 192 s.
The plasma current and density are kept constant during the whole duration. The
horizontal plasma displacement, AH, is well controlled within 3 mm.
Since the capability of the TRIAM-1M data acquisition system is not sufficient
to process all data of the more than three minutes of the discharge, we mainly studied
the discharge characteristics of a period of 60 s. We shall discuss these results. The
ion and electron temperatures were measured by charge exchanged neutral and soft
X-ray energy spectra, respectively.
Figure 3 shows typical results for the 60 s discharge. The time variation in
Fig. 3(a) indicates that the electron temperature of Te .= 1.0-1.2 keV and the ion
temperature of T, = 0.5-0.7 keV are maintained almost constant during the whole
duration. The ion temperature profile is close to the parabolic one, as shown in
Fig. 3(b); it is kept almost unchanged during the whole duration.
By assuming that the electron density and temperature as well as the ion temperature
have steady state profiles and that the RF power corresponding to the accessible
part of the N| spectra of the injected RF waves is absorbed by the electrons [2], we
have calculated the energy confinement time of the bulk plasma to be TE = 3 ms.
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