1 - Nuclear Sciences and Applications - IAEA

234 KAUFMANN et al.
E
1.2
Z 0.8-
? 0.4-
•l\
• \
V
Y \V\
\
VCQIC. Dnn=.8O m 2 /s
\
\
»=0.05\
\
i
—o——"*—"—- *• ' 0 "tt—Vi
0 0.1 0.2 0.3" " "r[m) 0.4
FIG. 5. Soft-X-ray intensity versus radius for t = 1.4 s.
In addition to the bolometer profiles the accumulation of Cu is also obvious from the
pronounced peaking of soft-X-ray profiles. These emission profiles are particularly suited
for a comparison with neoclassical transport simulations because of the suppressed
boundary radiation. In fig. 5 we show such a comparison for t=1.4 s when the shape of
ncu-profile has become stationary. The calculations are performed by adding neoclassical
fluxes [4]and anomalous diffusive fluxes Yan = —Dandnz/dr. Accumulation is
initiated by reducing Dan from typical values of 0.8 m 2 fs (t < 1.2 s at all radii) in the
inital phase to values of 0.05 m 2 /s in the inner region r/a < 0.75 for t > 1.2 s during
accumulation. This way the good agreement with the measured SX-profiles as plotted
in fig. 5 is obtained. The sensivity of this comparison with respect to the reduction of
Dan is indicated in fig. 5 by the curves for unchanged transport [Dan = 0.8m 2 fs =
const) and fully neoclassical transport Dan —* 0.
4. Global Energy Confinement
For standard values of Ip and Bt, the global energy confinement time TE was investigated
as a function of nc, heating power Ptot and isotope type [see fig. 6]. An additional
variation of confinement time with fuelling method can be well described as a further
dependence of TE on the density peaking parameter. Whereas, under purely Ohmic
heating, density scans for the usual gas puff-fuelled discharges with flat density profiles
(ne(0)/{ne) < 1.5) show a saturation of TE at 60 and 85 ms for H + and D + ,
respectively, and a subsequent decline with ne, pellet fuelling allows access to a regime
with peaked nt{j) and monotonically increasing r£;(ne) reaching values of 110 ms for
H + and 160 ma for JD + . However, also in this case, confinement deteriorates with
heating power, and the gain in TE of these peaked density profile discharges compared
to conventional, gas fuelled L regime cases decreases from a factor of nearly 2 at Ohmic
power levels (« 0.5 MW) to 1.3 at Ptot = 2;7 MW for H° =• D+ injection (fig. 6). At
the same time the maximum peaking factor of density achieved with pellet injection
diminishes from 2.6 to 1.6.
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