强径向电场剪切等离子体中涨落量引起的向内输运实验研究

Plasma transport is the focus of research on magnetic confined plasmas. The fluctuation induced transport has been compared with the equilibrium transport. Especially, for the anomalous transport leaded by plasma turbulence has become the research focus in recent decades. On the stellarator plasmas, it has been widely found that the strong radial electric field shear will cause the inward transportation. The threshold relation between radial electric field shear and inward transport is also given, but the mechanism of inward transport is not given further. Transport in tokamak research in this area of research is rarely involved. Recently, it has been observed that inward transport is triggered by strong radial electric field shear in the pedestal region of HL-2A tokamak, suggesting the inward transport may be related with the reconstruction of pedestal. The purpose of this project is to reveal the physical mechanism of the inward transport caused by strong radial electric field, which is very helpful for understanding the key role of radial electric field in reducing the anomalous transport and improving the confinement. The experiments will be completed in the domestic EAST, HL-2A and J-TEXT devices on the edge plasmas. These devices are capable of achieving strong radial electric field shear conditions in the edge region, providing a good platform for this topic research.

等离子体输运是磁约束等离子体研究的重点，涨落量引起的输运已经可以和平衡输运相比，特别对等离子体湍流引起的反常输运的研究成为了最近几十年的研究重点。在仿星器上很早就发现强径向电场剪切下会使得涨落量引起输运通量向内，即发现向内输运现象，并给出了径向电场剪切和向内输运的阈值关系，但并没有进一步给出向内输运的形成机制。在托卡马克输运研究中很少涉及这方面的研究，最近在HL-2A边界具有强径向电场剪切的台基区观测到了相干模导致的向内输运现象，暗示着向内输运可能和台基结构的重建有关。本课题的目的就是揭示强径向电场形成向内输运的物理机制，对于理解径向电场在降低反常输运改善约束的所起的关键作用有很大帮助。本课题的实验将在国内EAST、HL-2A及J-TEXT装置边界上完成，这些装置都能够在边界区域实现很强的径向电场剪切条件，都已经实现高约束模或具有约束改善迹象，为本课题的研究提供了良好的研究平台。

在本项目研究之前，许多研究猜测湍流引起的向内输运或与径向电场有关，但只是提供了一下表面的径向电场与向内输运的关联，并没有深入研究向内输运产生的机理。本项目执行之初，也猜测强径向电场是形成向内输运最关键的因素，但是随着研究的深入，特别是我们创造性地从输运方程出发重新推导形成输运各项，并在实验上逐项验证能够形成向内输运的可能项，让我们能够深入理解形成向内输运的本质。.我们首先在成都西南物理研究院的HL-2A装置上观测到一直向内输运的高频相干模，存在于台基区附近沿着电子逆磁漂移方向传播，然后首次在NBI临界功率加热产生H模实验中发现长寿模(Long-lived mode, LLM)诱发的向内输运，确认输运方向从向外到向内转变的直接原因是由于径向速度涨落的相位发生改变；从输运基本方程出发，加入不可压缩条件后仔细推导了能够产生向内输运的几项，并通过实验确定了导致向内输运的关键项，确认了非线性相互作用在驱动向内输运过程中的重要作用；最后还首次观测到低约束模(L模)放电芯部锯齿崩塌过程诱发的边界涨落向内输运现象，并从我们推导的输运项中获得解释。