On-axis ECCD by Strongly Focused mm Waves

点击翻译按钮获取中文摘要

The experiments have been carried out by using the WT-3 tokamak and its 89GHz ECH system. During the first year, suppression experiments of sawtooth oscillations by means of on-axis electron cyclotron current drive (ECCD) were done by using linearly polarized mm waves, and also improvement of ECH injection system for elliptically polarized wave injection was carried out. This year, we have done the suppression experiments by using improved ECH injection system and compared the results with the previous results of the linearly polarized wave injection cases. The major results are following :(1) Sawtooth oscillations are suppressed by on-axis counter-ECCD, while both inversion radius and amplitude of sawtooth oscillations are increased by on-axis co-ECCD. The former result may be due to the decrease of the on-axis current density, while the latter results may be due to the increase of the on-axis current density.(2) Elliptically polarized waves in the range of β=-37° 〜+37°(β being the ellipticity) can be obtained by a couple of corrugated mirrors. These results have been confirmed by cold and hot tests. Theoretical calculation shows that this improves absorption rate of injection power by 50% for the oblique injection of X-mode compared with the previous linearly polarized case at the injection angle of 60 degree to the toroidal field.(3) Above prediction is tested experimentally. The results shows that improvement of 20〜30% is obtained by the elliptic polarization, although 50% improvement can not be obtained. This discrepancy from the theoretical prediction may be due to the fact that single pass absorption is not complete in the present case.