Design of a helical system with the reduced toroidal viscosity

本课题研究的磁场位形最重要的特征是准轴对称(QA对称性)。这种对称性给出了磁场结构，当用布泽尔坐标表示时，该磁场结构不依赖于环形坐标。这种特性被称为二维场结构。然而，几何结构仍然是三维的，这是在没有环形等离子体电流的情况下产生旋转变换所必需的。这一点是托卡马克和QA星标之间的重要区别。我们为QA构型找到的解决方案之一被称为2b32，它具有环形周期N=2和平均长宽比3.2。这一长宽比在所有螺旋系统家族中是相对很低的，被认为有利于未来紧凑型螺旋反应堆的设计。2B32配置具有平坦的旋转变换轮廓(IOTA=0.4)，并为a…提供了良好的磁流体稳定性对于各种理想的MHD模式(Mercier和全球气球模式)，更多的版本Beta为4%。与传统的螺旋系统非常不同的是，它在半径的所有位置和贝塔的所有范围内都有一个磁势井。在低碰撞度条件下，新经典输运系数比传统螺旋体系降低了约两个数量级。除了经典的限制性质评估中的这些优点外，这种新的构型还有可能给出针对反常输运现象的改进的限制模式。环形系统中改进约束的一个重要模型是减少由于径向电场的陡峭梯度引起的剪切流动引起的湍流。为了创造这样的条件，低粘度的等离子体旋转运动是必要的。与传统的螺旋体系相比，我们的新构型具有小两个数量级的新古典主义粘度。还对2B32结构进行了工程设计，该结构有20个模块线圈，主半径为1.5米，磁场为1.5特斯拉。较少

The most important characteristics of the magnetic field configuration which has been studied in this research project is the quasi-axisymmetry (QA symmetry). This symmetry gives the magnetic field structure which does not depend on the toroidal coordinate when expressed in the Boozer coordinates. This characteristics is called as a two dimensional field structure. However the geometric structure is still three dimensional which is necessary to create the rotational transform without a toroidal plasma current. This point is important difference between tokamaks and QA stellarators. One of solutions we found for QA configurations is called 2b32 which has toroidal periods N=2 and the average aspect ratio 3.2. This aspect ratio is relatively very low among all family of helical systems and is considered to be advantageous for the design of compact helical reactors in the future. 2b32 configuration has a flat profile of rotational transform (iota=0.4) and gives good MHD stability for the a … More verage beta 4% against various ideal MHD modes (Mercier and global ballooning modes). It has a magnetic well for all positions of radius and all range of beta which is very different from the conventional helical systems. The neoclassical transport coefficients are reduced by about two orders of magnitudes in the low collisionality from the conventional helical systems. Besides these advantageous features in the classical evaluations of confinement properties, this new configuration has possibilities of giving improved confinement modes against anomalous transport phenomena. An important modeling of the improved confinement in toroidal systems is the reduction of the turbulence due to a sheared flow caused by the sharp gradient of the radial electric field. In order to create such a condition, low viscosity for the plasma rotating motion is necessary. Our new configuration has a two orders smaller neoclassical viscosities compared with conventional helical systems. The engineering design was also made for 2b32 configuration which has 20 modular coils with 1.5 m major radius for 1.5 Tesla magnetic field. Less