1 - Nuclear Sciences and Applications - IAEA

1.0
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Minor Radius ( cm )
IAEA-CN-50/A-V-3-1 289
g.
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i i i i
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Minor Radius ( cm )
FIG. 2. (a) Normalized electron density and (b) normalized ion temperature profiles of ohmically
heated plasmas with ne = 2.5 x ldf 9 m' 3 (solid line) andne = 5.2 x JO 19 m' 3 (dashed line).
(b) correspond to the directions of the electron diamagnetic drift and the ion diamagnetic
drift, respectively, and vice versa in Figs l(c) and (d). In the low density
regime, the main part of the density fluctuations propagates in the direction of the
electron diamagnetic drift (Figs l(a) and (c)), having a linear dispersion relation for
various wavenumbers. In the high density regime, the ion mode propagating in the
ion diamagnetic drift direction is observed (Figs l(b) and (d)). This ion mode is considered
to be the drift instability driven by ion temperature gradient, which may cause
anomalous ion thermal transport in high density OH and auxiliary heated plasmas.
To study the drift wave turbulence, it is important to examine the spatial profiles of
the density and the temperature. Figure 2 shows the normalized electron density and
ion temperature profiles for the OH plasmas in the low and high density regimes. The
value of ij; = (d In T/d In n;) in the high density case is about 1.0-1.2 at
r/a * 0.5, and in this plasma the ion mode is clearly observed. This value is comparable
to the threshold value (—0.95) estimated theoretically for the instability with
kxPi - 1 [6].
Figure 3 shows the temporal behaviour of the plasma parameters in the ICRF
heated discharge (PRF » 800 kW). During the OH phase, the stored energy
increases with increasing line averaged electron density up to 4 X 10 13 cm" 3 , and
saturates in the high density region of 5, S 4 X 10 13 cm" 3 . The electron mode
component fte(e) increases with the electron density. On the other hand, the ion
mode component fi^i) keeps a constant level in the low density region
(% £ 4 x 10 13 cm" 3 ) and starts rising clearly when % increases above
4 x 10 13 cm" 3 . Injection of ICRF power at t = 255 ms remarkably enhances both
components of the density fluctuations. The injection of an ice pellet in the course
of the ICRF pulse also drastically increases the amplitude of both components just
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