1 - Nuclear Sciences and Applications - IAEA

E6950(Bi=4.0T)
E6956(Bt = 2.7T)
°46 5.0 5.5 6.0 6.5 7.0 7.5
TIME(S)
IAEA-CN-50/A-V-1 267
h-> IMPROVED
4.5 5.0 5.5 6.0 65 70 75
TIME(S)
FIG. 1. Comparison ofl MA discharge waveforms with and without improved confinement. The thick
lines stand for traces of an enhanced shot (E6950; B, = 4T, q^f "3.7) and thin ones for a low-q shot
(E6956; B, = 2.7T, qtff » 2.4).
There is, however, a threshold for the heating power (—15 MW) to achieve the
improvement.
The IDC regime is easily obtained at high B,, whereas clear H-phases are
observed only in low B, discharges. Figure 2 shows the points where IDC regime,
L/H transitions and ELMs appear in the domain of line averaged electron density and
absorbed power. L/H transitions were observed in low density discharges for Bt
around 3 T. The IDC regime sets in afterwards at higher electron densities. When
Bt is higher, the IDC regime starts at lower electron densities. The threshold i^
increases with power in both cases. Since the connection length of the magnetic field
lines from the plasma edge to the divertor plates increases with Bt, these findings
suggest that the IDC regime is related to the formation of dense and cold divertor
plasmas [9, 10]. The time evolution of the divertor plate temperature is measured
with an infrared camera. An example for these measurements is shown in Fig. 3. It
should be noted that the rate of temperature increase drops when the IDC regime sets
in around 5.7 s. The heat flux onto the divertor plates which is evaluated with a 1-D
heat inverse conduction code decreases during the IDC regime. The total power load
at 6.7 s is estimated to be about 4 MW, on the assumption that the heat flux profile
is similar to the temperature profile. The values of the radiation power from main
and divertor plasmas are about 4 MW and 9 MW, respectively. Thus, the total