1 - Nuclear Sciences and Applications - IAEA

0.3
f0.2
1 5" 0.1
IAEA-CN-50/A-IV-l 225
RF Heating /
#i62n k—s^r-
#16227
J
0 0.2 0.4 Radius (m) 1.0
10
r=0
_ 8
r
Ohmic
. r/a-6.5
JE 6
1.4
10
s~* 8
• r/a=0.75
r/a=0.75
0.2 0.4 0.6 0.8
Time (s)
RF Heating
FIG. 8. Particle diffusion coefficient for Ohmic and RF heated cases. Evolution of density profile,
measured (solid curves) and calculated (dashed curves), at four radii in Ohmic and RF heated cases.
becomes more rapid. A similar radial variation in the diffusion coefficient is
sufficient to model this change, when a 20% increase in the edge value is included.
Again the neoclassical pinch is assumed. However, a wide variation in decay rates
is observed when a range of heated pulses is modeled. In some cases this
simplified model cannot reproduce the increased decay rate. A significant
increase in core diffusion is required, suggesting that another mechanism may be
triggered which can further accelerate the central electron density decay.
During the ohmic phase, impurity transport both of nickel (high Z) and carbon
(low Z) within this weakly anomolous central region is found to be consistent with
neoclassical transport[17]. During the heating phase, impurity transport can
remain consistent with neoclassical theory within the plasma core until the
termination of the enhanced period. In this phase, impurity transport may reflect
the appearance of an ion temperature driving term[17].
4. Summary
A transient enhanced performance mode has been obtained in JET limiter
discharges using pellet injection fueling in combination with central RF heating.
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