1 - Nuclear Sciences and Applications - IAEA

2.0
. P« (MW)
\PNBI
800 1000 1200 1400 1600 1800
TIME (msec)
IAEA-CN-50/E-I-2
61393 61393
535
800 1000 1200 1400 1600 1800
TIME (msec)
FIG. 5. Traces for a discharge (61393) with 1.25 MW of neutral deuterium injection and 0.9 MW of
ECH. Plasma current is 0.6 MA and toroidal field is 2.1 T. W is determined from MHD analysis, Da
emission is measured in the divertor region, and Te(0) is determined from ECE.
plasma edge. The improvement in re, from values near the Kaye-Goldston
level to the ohmic value, is shown in Fig. 3. The correction to re due to
dWfdt is necessary because after the transition to H-mode the density begins
rising and continues to rise until the ECH cutoff density is exceeded,
at which time a reverse transition to L-mode takes place. For this reason,
no steady state in fie or W was obtained during the H-mode. Using outside
launch 0-mode fundamental heating at 2.1 T, the H-mode regime of
improved confinement was not attained at the ECH power levels available
(1.1 MW).
Transport analysis of the H-mode discharges generated by second
harmonic ECH shows a decrease in electron thermal diffusivity Xc by a
factor of 2 to 4 compared to that during the L-mode [9]. The ECH data
has been analyzed with the l|D transport code ONETWO [13], with
the power deposition calculated by TORAY. Electron temperature and
density profiles are found from Thomson scattering and ion temperature
profiles are obtained from charge exchange recombination emission. The
values of Xe and %i are determined for the region 0.25 < r/a < 0.75, and
the largest decrease in Xe occurs for r/a < 0.5. The xi * s found to be
roughly a factor 6 larger than neoclassical, and it is not much affected by
the H-mode transition. This behavior is shown in Fig. 4. These results
show that the increase m energy following the H-mode transition is due
to an improvement in electron thermal diffusivity as well as in particle
confinement.
In order to determine the scaling of the power threshold for H-mode
with Bt, experiments were performed with combined neutral injection
and ECH using the fundamental 0-mode. Figure 5 shows data from a
discharge which entered the H-mode promptly when 1.0 MW of ECH was