Study of Self organization of current hole in high confinement plasma

本研究的目的是阐明在JT-60U大型托卡马克上观察到的电流空穴自组织的机制。主要研究结果如下：1.提出了等离子体中心电流几乎为零的平衡三磁岛模型。得到了ATMI模型稳定存在的条件。2.研究了具有类似电流孔的强空电流分布的等离子体的MHD稳定性。分析表明，在强逆剪切区存在通过调整压力分布和电流分布来获得高β等离子体(β_N&GT；4)的可能性。3.通过对1.5维输运模型的模拟与在JT-60U上的实验观测相比较，研究了电流空穴的形成和维持。结果表明，由于强内输运势垒(ITB)的形成和反常输运的快速下降，由于局部自举电流的增大，负电场的穿透使电流空穴自组织。通过MHD模拟，研究了负电场作用下等离子体对电流的响应，得到了电流空穴形成对涡旋的解释。电流空穴等离子体在等离子体中心附近有很强的ITB和新经典能级输运，通过调节压力和电流分布，有可能成为很高的β能级。因此，使用电流空穴的托卡马克聚变反应堆有可能成为一种极高效率的反应堆。

Purpose of this study is to clarify the mechanism of self-organization of current hole observed in JT-60U large tokamak. The following results are obtained.1.Tri-magnetic island (ATMI) model is proposed as equilibrium with nearly zero current around the plasma center. The condition of the stable existence of the ATMI model is obtained.2.MHD stability of plasmas with strongly hollow current profile like the current hole is investigated. Analysis shows that the possibility to obtain the high beta plasma (β_N>4) by tailoring the pressure profile and the current profile such as the pressure gradient exists in the strong reversed shear region.3.Formation and sustainment of the current hole are investigated by the comparison of simulations of the 1.5 dimension transport code using the ATMI equilibrium model with experimental observations in JT-60U. Results show that both of the formation of strong internal transport barrier (ITB) and the rapid drop of the anomalous transport makes a self-organization of the current hole by the penetration of the negative electric field due to the increase of the local bootstrap current. Also, the energy confinement law within the current hole and the property of the sustainment by using the current drive are clarified.4.By the MHD simulation, the response to the plasma with negative electric field is investigated, and the formation of the pair vortices is obtained as an explanation of the current hole. The interaction of the pair vortices and the residual magnetic field removes the negative electric field.The current hole plasma has the strong ITB and the neo-classical level transport near the plasma center, also it has a possibility to become a very high beta by tailoring the pressure and current profiles. Therefore, the tokamak fusion reactor using the current hole has a potential to become an extremely high efficiency reactor.