1 - Nuclear Sciences and Applications - IAEA

0.20
0.15
0.10
Rp= 2.45 m
a = 0.79 m
BT = 4.7-5.0T
IAEA-CN-50/A-I-2 37
0.05
0.5 1.0 1.5
PLASMA CURRENT (MA)
O
L-Mode
Scaling
FIG. 7. Scaling of the energy confinement time with plasma current for discharges with nearly
balanced NBI and well-conditioned limiters. Data for lower current (< 1 MA) supershots from 1986 and
1987 are included. The upper bound of the L-mode region, which encompasses data for all NBIpowers
in the data set, is determined by the lowest power at each current.
comparison for the range of current and power in the data set; the upper
boundary corresponds to discharges at 1.6 MA.
The confinement time is shown in Fig. 7 as a function of plasma current.
This data set includes not only the recent data (Fig. 6) but also data from
1986 and 1987 to include the lower currents (/p < 1 MA). The constraints
which were applied to the data shown in Fig. 6 were applied here. The
local peak in the confinement time at 0.9 MA reflects the situation in 1986
and 1987 when attempts to increase the plasma current resulted in a rapid
degradation of performance. The improvement in conditioning in 1988,
coupled with the higher balanced NBI power, has improved the performance
at 1.4 and 1.6 MA (the currents at which experimental running has been
concentrated) to levels comparable to that achieved in the early supershot
experiments. The upper limit to the band representing L-mode data is
calculated for the minimum power included for each current.
The QDD (= PDD/PNBI) for a subset of discharges satisfying the same
constraints on co/counter-injection balance and target density is shown in
Fig. 8 as a function of NBI power. As expected on the basis of Fig. 2, QDD
increases strongly with power, but again there is no obvious scaling with
current at each power level. There is a small but significant group of shots
with QDD substantially higher than the envelope of the bulk of the data.
These discharges occur at the lowest extremes of the target density range. It
is possible, therefore, that further improvements in conditioning techniques
will allow reliable access to these exceptional conditions.
2.0