1 - Nuclear Sciences and Applications - IAEA

372 TARONI et al.
3.2 3.4 3.6
Radius (m)
FIG. 3. (a) Experimental profiles ofTe, 7) and ne for a pellet shot (17279). Superscript I refers to the
phase of enhanced confinement (t, = 44.6), superscript 2 to the following 'normal' phase (t2 = 45).
TJ is fr om ECE, n[ from Abel inversion of interferometer data; T 2 t and n\ are from Lidar (not
available for phase J); TJ and if from charge exchange spectroscopy. (b) 'Experimental' thermal
conductivity x = X, + ("jV T/n^V Tjxi and values of rje and TJ, at R = 3.4, t = t, and t2. Similar
values of-r\e and ij, are obtained from Lidar data during phase 1 of other discharges. The neoclassical
(Chang-Hinton) value ofxt at t, is given for comparison.
the enhanced confinement phase; the correlation, observed so far,
with the evolution of the current density profile [4].
Comparison of "Experimental" and Theoretical Heat Fluxes
A number of models for local energy transport available in the
literature (see [7,12] and the references quoted in [13]) has been
compared with experimentally determined heat fluxes, in a series of
ohmic, sawtoothing L-mode and "monster" discharges.
Local agreement within a factor of 2 between modelled and
measured heat flux is accepted as fairly good, keeping in mind the
uncertainties in "experimental" fluxes and the strong non-linearity
(e.g. local dependence of xe on VTe) of most theoretical models.
Our results indicate that in the region outside q^ = 1, where
meaningful comparisons are possible, the resistive mhd model (PT
model) [12] and the Rebut-Lallia (RL) model [7] predict energy
fluxes in fair agreement with the observed ones. For the RL model,
the discrepancy increases when VTe approaches the local critical
gradient VCT (typically, near the plasma edge), suggesting that the
transition to low transport below VCT might have to be smooth
rather than sudden. In the same region, pure drift wave models
fail to reproduce radial dependence and magnitude of the measured
fluxes [13,14], The microinstability-profile consistency model of
Tang [13,15], rescaled by a factor 2 is in agreement with JET
data.