Confinement Improvement with Simultaneous Achievement of Magnetic Well and Stellarator Shear in Helical Plasma

在NBI加热的CHS螺旋等离子体中发现了新的约束区。它的特点是在芯区电子温度沿边缘输运势垒沿着显著升高。在NBI等离子体中经常观察到边输运势垒，其特征是Ha信号的突然减弱。另一方面，在低电子密度的ECH等离子体中，通常观察到随着核心电子温度升高的内部输运势垒。这种新的放电的电子密度（3- 4 × 10 ~（13）m <19>~ 2<-3>）比具有内输运势垒的电子根等离子体的电子密度（3- 4 × 10 ~（13）m ~ 2）高约一个数量级<18><-3>。根据强喷气，电子密度增加，导致等离子体β增加。在0.9特斯拉的磁场强度下，通过增加电子密度，等离子体β毫无困难地达到约0.5%。这导致磁阱在芯区域中，尽管它是浅的。当施加强气体时，即使在NBI等离子体中，电子密度分布也变得中空。电子温度的时间演化表现出一个快速的增加，随后相当迅速的下降，时间尺度为几毫秒。即使在有限的β等离子体中，CHS也存在仿星器切变。人们试图用磁阱和仿星器剪切同时实现的漂移反转来解释这一现象，但没有成功。然而，当绝热近似不成立时，可以用空心密度分布下的交换稳定性来解释。

New confinement regime has been found in CHS helical plasma heated with NBI. It is featured with remarkable electron temperature increase in the core region along with the edge transport barrier. The edge transport barrier is usually observed in NBI plasmas characterized with the abrupt reduction of Ha signal. On the other hand, the internal transport barrier with the core electron temperature increase is usually observed in ECH plasmas with low electron density. The electron density (3-4x10^<19>m^<-3>) of this new discharge is higher by about one order than that (3-4x10^<18>m^<-3>) of the electron-root plasma featured with the internal transport barrier. According to the strong gas puff the electron density increases, resulting in an increase in the plasma p. At the magnetic field strength of 0.9 Tesla the plasma β reaches about 0.5% without any difficulty by increasing the electron density. This causes the magnetic well in the core region although it is shallow. When strong gas puff is applied, the electron density profile gets hollow even in the NBI plasma. The temporal evolution of the electron temperature shows a rapid increase followed by a rather rapid decrease with the time scale of a few milliseconds. CHS has a stellarator shear even in the finite β plasma. This phenomenon was tried to explain by the drift reversal that is realized under the simultaneous achievement of the magnetic well and the stellarator shear, but in vain. However, it could be explained with the idea of the interchange stability under the hollow density profile when the adiabatic approximation for electrons does not hold.