Design of a helical system with the reduced toroidal viscosity

在本研究项目中所研究的磁场结构的最重要的特征是准轴对称性（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，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，这对于在没有环形等离子体电流的情况下产生旋转变换是必要的。这一点是托卡马克与QA仿星器的重要区别。我们发现的QA配置的解决方案之一是所谓的2b 32，其具有环形周期N=2和平均纵横比3.2。该纵横比在所有螺旋系统家族中相对非常低，并且被认为对未来紧凑螺旋反应器的设计是有利的。2b 32位形具有平坦的转动变换轮廓（iota=0.4），并对α-Al_2O_3具有良好的MHD稳定性。 ...更多信息 与各种理想MHD模式（Mercier和全局气球模式）相比，β值为4%。它有一个磁井的所有位置的半径和所有范围的β这是非常不同于传统的螺旋系统。在低碰撞度下，新经典输运系数比传统螺旋系统降低了两个数量级。除了这些优点在经典的评价限制性能，这种新的配置有可能给改善限制模式对异常传输现象。环形系统中改进约束的一个重要建模是减少由于径向电场的急剧梯度引起的剪切流而引起的湍流。为了形成这样的条件，等离子体旋转运动的低粘度是必要的。与传统的螺旋系统相比，我们的新构型具有小两个数量级的新经典粘度。还针对2b 32配置进行了工程设计，该配置具有20个模块化线圈，主半径为1.5 m，磁场为1.5特斯拉。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