D. Pacella et al., DIRECT MEASUREMENT OF THE IMPURITY RADIAL FLUX IN THE FTU PLASMA CORE, Plasma physics and controlled fusion, 39(10), 1997, pp. 1501-1508
A direct measurement of the impurity radial flux in the FTU plasma cor
e has been obtained by observation of soft x-ray spectra from highly i
onized charge states of intrinsic molybdenum. This measurement has bee
n performed using the equation of continuity for Mo31+ and the radial
density profiles of Mo32+, Mo31+ and Mo30+. The profiles of these ions
have been obtained by inversion of the measured signal along six diff
erent lines of sight in a series of reproducible discharges. Other ion
s. such as Fe and Ni, which emit in the VUV range, are also monitored
at different chords and confirm the picture given by the soft x-ray me
asurements. A collisional-radiative model developed at LLNL and JHU al
lowed the reconstruction, from the spectra, of the radial profiles for
the three molybdenum ions. The resulting flux Gamma(31+) shows that t
he transport is negligible (within the experimental errors) in the cen
tral region r < 10 cm, but is very rapid in the intermediate region 10
< r < 20 cm, and is more than one order of magnitude greater than the
neoclassical prediction. Defining an effective 'radial drift velocity
' V-r = Gamma(31+)/N31+, it is found that V-r has its maximum at half
radius and there its value is about 0.4% of the thermal velocity.