1 - Nuclear Sciences and Applications - IAEA

2 /s)
I.OH
O.I-
10-
Im 2 /sl
10-
0.1
IAEA-CN-50/A-m-l 153
soc
#17 529 co-NI(L)
# 23 349 -57
1.8-2.1 s
#21621
t = 1.715 s
ctr .
05 r/a 10 0 0.5 r/a
FIG. 6. Radial profiles of electron and ion heat diffusivities \e and Xifrom transport code calculations
for regimes of degraded confinement (SOC, co-NI) and of improved confinement (IOC, ctr-NI).
L-periods. After a transition, ne rises throughout the H-phase; j3p, however, rises
only transiently and decreases thereafter. These observations suggest that the advantage
of peaked n^r) profiles cannot be maintained after the H-transition as the
H-mode broadens n,.(r).
Transport studies. In a comparison study the transport in the IOC and SOC
regimes and with co- and ctr-NI, respectively, has been analysed using the TRANSP
code [6]. The radial variation of xe is determined such that agreement with the
measured plasma parameters and profiles is obtained. The ion heat conductivity
coefficient XJ is taken from theory and put into the model.
The Xi models used are either the neoclassical XCH as given in Ref. [7], or the
sum of XCH an d X^i a s given in Ref. [8]. These assumptions were based on
experience in analysing previous SOC and L-mode co-NI cases on one hand, and
pellet refuelled plasmas with peaked density profiles on the other [9]. Radial profiles
of the heat diffusivities are shown in Fig. 6 for the degraded and improved confinement
regimes. The low confinement cases with broad density profiles can consistently
be described with an anomalous ion heat diffusivity due to ion temperature
gradient (ITG) driven turbulence. For the cases of peaked density profiles the
parameter r;, = d In T/d In r^ is strongly reduced to values near or even below 1,
over most of the plasma cross-section. Under this condition ITG modes should be
stabilized. In fact, in TRANSP calculations these cases can be described with
neoclassical ion heat transport only. Additionally, the electron transport seems to be
IOC