1 - Nuclear Sciences and Applications - IAEA

186 ZARNSTORFF et al.
X-ray spectroscopic measurements of metallic concentrations. The radiated
power profile is measured by three bolometer arrays. Edge hydrogenicneutral
influx is inferred [7] from the measurements of an array of absolutely
calibrated Ha detectors. The beam-ion slowing down distribution is simulated
as a separate species not subject to anomalous transport, consistent
with experimental observations [8,9]. The beam ions are treated as joining
the background thermal ion species when their energy falls to |Ti. Electronion
energy exchange is assumed to be classical.
The total stored energy and neutron emission rate calculated by this simulation
are typically in good agreement with the experimental measurements
(maximum deviations of < 10% for stored energy, < 25% for neutron flux -
roughly the present measurement uncertainty). For the supershot shown in
Fig. 1 the analysis indicates that nb/ne — 0.14 on axis, and that the beam
stored energy is 41% of the total. While the global energy confinement time
is 0.18 sec, the calculated energy confinement time of the thermal component
is 0.12 sec.
The calculated neutral beam power and particle source profiles are very
peaked on axis. The central power density of 4 MW m~ 3 and beam fueling
is the dominant particle source for r < |a. The central energy transport
(both for ions and electrons) is dominated by convection for r < a/3. In this
region, it is found that Qi/TiTi is bounded from below by ~ | and Qe/TeTe
by 2 - 2.5, where Qi (Qe) is the total ion (electron) heat flux and I\ (re) is
the ion (electron) particle flux [10]. Thus, use of the usual convective heat
flux of |r\7; would require an unphysical negative Xi m the central region.
For the present paper the electron and ion thermal difFusivities Xe an d Xi are
defined by Qe = neXeVTe + \Y£Te and Qi = n^Ti + fl^T;, where n; is the
total thermal ion density, unless otherwise noted.
The ion thermal diffusivity with neutral beam heating, see Fig. 2, is found
to be much larger [11] than predicted by neoclassical theory[12], as previously
found on Doublet III [13]. In all plasmas analyzed, the measured T± profile is
narrower than predicted by neoclassical transport, with the prediction being
well outside the error-bars of the measurements. The central ion temperature
is not in strong disagreement with the neoclassical prediction due to the
dominance of the convective heat flux in the central ion power balance. The
outer region of the predicted Ti profile is determined by the assumed classical
ion-electron energy exchange, which dominates the predicted neoclassical
transport. The inferred Xi IS U P to 40 times larger than the neoclassical
prediction in the outer region of the plasma, emphasizing the importance
of Ti profile measurements to the understanding of thermal transport. The
analysis indicates that in the outer region x% an d Xe have similar magnitudes
and profile shapes. The error-bars on Xe and Xi m the figure (and subsequent