1 - Nuclear Sciences and Applications - IAEA

142 HUO et al.
O.O7
0.04
0.19
0.06
0.13
0.07
0.17
0.08
0.18
0.08
0.07
0.04
-0.82
•0.85
5.0 7.0 9.0 11.0
ms
13.0 15.0 17.0
FIG. 4. From top to bottom: line emission signals of O(III) (at 1.5 and 8.7 cm), C(III) (at 1.5 and
8.7 cm) and Ha (at 1.5 and 8.7 cm), and RHF current (inverted).
In Fig. 4, Ha radiation behaved differently from impurities. It rose in the first
2 ms and immediately decayed to its original value, without significant change when
the RHF was turned off. This showed that there was no greatly intensified hydrogen
influx during that period.
The above results showed that the weak RHF magnetic perturbation would
change the MHD instabilities and the sawtooth behaviour, as well as the plasma confinement.
On the other hand, the effectiveness of the RHF depended on the discharge
conditions. The RHF was not effective in high Zeff discharges. The RHF configuration
(£ = 2 or 3) had to be chosen for discharges with different q values and profiles.
The optimal RHF current was related to plasma density. This meant that the mechanism
of the RHF could not be simply considered as a direct magnetic interaction with
MHD mode.
4. SUMMARY
The main experimental results can be summarized as follows:
(1) The RHF could reduce energy and particle losses and improve plasma confinement.
RHF discharges have higher density and broader temperature profile.
(2) The RHF produced large sawteeth characterized by their amplitudes, periods
and slopes and the range over which the sawteeth spread. The large amplitude
sawteeth with strong collapses decreased the mean value of the temperature at
the plasma core. It is unclear why the driving force of the collapses was intensified
and what the nature of the driving force is.