Development to new stage of helical plasma confinement

1) CHS-qa的物理和工程设计取得进展，有望成为后chs设备。稳定性β高达4%，实现了高能离子的良好轨道约束。高性能导致等离子体截面的高伸长率。2)利用新古典理论的有效螺旋纹波估计了CHS等离子体高离子温度模式的离子热扩散率。估计值与实验值接近。估计了在螺旋波纹底部具有相同磁场强度的情况下，磁轴强烈向内移动所实现的准均匀构型离子的扩散系数。准均匀结构的预期离子温度为1.5keV，远高于目前在1keV的高钛模式下获得的值。3)由于CHS中的电位分岔导致了电子的约束改善，从而导致了高电子温度模式，实现了2keV的高中心电子温度。在T-10托卡马克中也观察到相同的内部传输障碍现象。两种等离子体（CHS和T-10）在径向电场剪切较强的位置形成输运屏障。4)定性地解释了平衡β值随等离子体截面伸长率的增加而增加的现象。伸长率应该在获得高性能等离子体方面发挥作用。结果表明，磁测量不能唯一地确定环形等离子体的电流和压力分布。

1) Progress has been made on physics and engineering design of CHS-qa, which is supposed to be a post-CHS device. Stability β up to 4% and good orbit confinement of high energy ions have been achieved. High performance results in high elongation of plasma cross-section. 2) Ion thermal diffusivity of high ion temperature mode of CHS plasma has been estimated by using the effective helical ripple of the neoclassical theory. The estimated values are close to the experimental one. The ion diffusivity for quasi-omnigenous configuration realized by a strong inward shift of the magnetic axis, where the bottom of helical ripple has the same magnetic field strength, has been estimated. The expected ion temperature for the quasi-omnigenous configuration is 1.5keV, which is much higher than the value obtained so far in high Ti mode of 1keV. 3) Confinement improvement of electron results from the potential bifurcation in CHS, which leads to the high electron temperature mode where high central electron temperature of 2keV is realized. The same phenomenon of the internal transport barrier has been observed in T-10 tokamak. The transport barrier is formed at the position where the radial electric field shear is strong for both plasmas (CHS and T-10). 4) Qualitative explanation has been made on the fact that the equilibrium βvalue increases as the elongation of plasma cross-section increases. The elongation should play a role in getting a high performance plasma. It is shown that magnetic measurements can not determine uniquely the current and pressure profiles of toroidal plasmas.