1 - Nuclear Sciences and Applications - IAEA

554 MOTOJIMA et al.
(a)
0.6SneS0.9x10 1J cm" J
0.S 1.0
TglO) (keV)
0.5 1.0
Te(0) (keV)
FIG. 3. (a) Observed poloidal rotation velocity versus Tc; (b) calculated result for Er obtained by onedimensional
simulation code.
An attempt to reduce ripple transport was made by shifting the magnetic axis
inward. By using an additional vertical field Bv, the magnetic axis could be shifted
inward or outward, depending on the direction of Bv. When the magnetic axis was
shifted inward (A < 0), the helical ripple became localized on the inboard side of
the torus. An improvement of transport was expected [7]. In the opposite direction
(A > 0), transport was expected to be enhanced. Figure 4 shows the dependences
of the Te, Tj, at and the decay time rd of Te after RF turnoff on the axis shift, A.
The line density was kept constant around 7 x 10 14 cm" 2 , with constant gas puffing
rate. When A = -2 cm (A/a,, - 0.1), Te and Ts increased by -15%. At further
inward shift, A = -4 cm, Te and Tj started to decrease. In the case of an outward
shift, they decreased monotonically. To indicate the improvement of the confinement
in the central region, TA within r/a < 0.2 was also plotted. It was the longest at
A = -2 cm, being improved by ~ 20% over the case of A = 0 cm. Thus, aplasma
with higher temperature and longer confinement time was obtained by shifting the
magnetic axis inward. This improvement factor was larger than the expected value
(~ 10%), if rE scaled as a£. Considering the deviation of the magnetic axis from the
unshifted mod-B structure, both inward and outward shifts were expected to cause
almost the same change in the absorption profile. Therefore, even if the confinement
was related to the absorption profile, the fact of an improvement for A = -2 cm and
a degradation by A = +2 cm could not be explained by this profile effect. The fact
of higher Te and longer rd suggested a reduction of the transport coefficient.