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

点击翻译按钮获取中文摘要

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.