Study of Potential Structural Reformation with multi-channel measurements using heavy ion beam

点击翻译按钮获取中文摘要

In the first two fiscal years from 2000 to 2001, we had constructed a new heavy ion beam probe (HIBP) system on CHS in addition to the old HIBP system. The new HIBP is located at the position away from the old one by 90 degree in toroidal direction. During this period of the construction, we had also made experimental efforts to obtain further understanding of bifurcation characteristics. In these experiments, we have obtained new findings about patterns of bifurcation and existence of hysteresis for realization of the status with improved confinement. These results have been published in Nuclear Fusion. Furthermore, the integrated paper including the results obtained in the phase when CHS is in the Higashiyama site has been also published in the book entitled 'Bifurcation phenomena in plasmas'. In the fiscal year 2001, the construction of the new HIBP has been finished, and the first experiments using two HIBP systems have been done on the ECR-heated CHS plasma with a low electron density of 0.5x10^<13> cm^<-3>. The simultaneous measurements at two different radial positions with these two HIBPs give us information of spatio-temporal evolution of potential structure during electric pulsation (self-organized oscillation). The result has been presented as a post dead line paper in 19^<th> IAEA conference on fusion energy. The outline of the results is following, i) During the pulsation, the potential drop propagates from the center to the outside, and the propagation is quite high. If we express the propagation as diffusion process, the coefficient is D-100m^2/s. ii) It is found that the edge density is strongly correlated with central potential behavior. The observation shows non-local nature of this phenomenon, iii) In the same series of discharges, coherent fluctuation has been observed in potential. The fluctuation is considered to relate with Alfven modes and the corresponding displacement of magnetic surface has been deduced.