Joint Study on Confinement Improvement in Helical Systems

目前的合作项目已成功地进行了1994年和1995年两年。我们取得了丰硕的成果，主要包括四个方面：（1）MHD稳定性;（2）轨道-核经典输运-加热;（3）磁表面岛的形成和破裂;（4）反常输运和约束改进的新模型.全三维稳定性程序CAS 3D与二维稳定性程序RESORM的比较和基准测试基于仿星器展开和平均法的等离子体稳定性计算结果在两者之间有很好的一致性。高n气球模的三维分析表明，该模式可以是不稳定的正磁剪切的heliotron螺旋系统的模式是稳定的托卡马克。发现低n气球模在螺旋系统中的行为与托卡马克中的不同，并将新经典理论推广到一般的环系统中。结果发现，在螺旋系统中存在与径向电场成正比的自举电流，这在托卡马克中是不存在的。因此，可以减小自举电流。如果它在方向上流动，以减少旋转变换，可以稳定的交换模式，导致改善约束.岛的形成和相关的磁表面的破碎，用平衡程序“HINT”进行了研究.发现了导致约束改善的“自愈”现象，提出了螺旋系统和托卡马克中反常输运的新模型，解释了一些未解决的实验事实。

The present collaboration project has been done successfully for two years of 1994 and 1995. We have obtained fruitful results which consist of main four categories ; (1) MHD stability, (2) Orbit-neclassical transport-heating, (3) Island formation and breaking of magnetic surfaces, and (4) New model for anomalous transport and confinement improvement.The comparison and the benchmark test of the full three dimensional stability code "CAS3D" and the two dimensional stability code "RESORM" based on the stellarator expansion or the average method have yielded a good agreement between the two for the stability of the LHD plasma. Three dimensional analysis of the high-n balloning mode revealed that the mode can be unstable for positive magnetic shear in the heliotron helical system for which the mode is stable in the tokamak. The low-n balloning mode has been found to behave differently in the helical system from in the tokamak.The neoclassical theory has been developed to the general toroidal system. As a result, it has been found that the bootstrap current proportional to the radial electric field, which does not exist in the tokamak, exists in the helical system. Thus it is possible to reduce the bootstrap current. If it flows in the dirrection to reduce the rotational transform, the interchange mode can be stabilized, resulting in improvement of the confinement.Island formation and related breaking of magnetic surfaces have been studied by using the equilibrium code "HINT". The "Self-Healing" phenomenon has been discovered which leads to the confinement improvement.A New model for the anomalous transports in helical systems as well as tokamaks has been proposed and explained some unresolved experimental facts.