磁剪切和磁环形曲率在非局域电子热输运中的作用

There are two kinds of nonlocal electron heat transport events observed separately in experiment at lots of tokamaks around the world since 1990s. One is that the core electron temperature increases abruptly about 1ms after a cold pulse (i.e., impurity, pellet or supersonic molecular beam) is injected near the edge of tokamak, so called opposite polarity. The other is that the electron temperatures both at the core and whole space increase abruptly about 1ms after a heat pulse (i.e., electron cyclotron resonance heating, neutral beam heating) is injected near the edge of tokamak, so called profile resilience. Both opposite polarity and profile resilience have the same characteristic time and length scales. Their time scales are greater than turbulent eddy decaying time but much less than the edge-core heat collisional diffusion time at Gyro-Bohm scaling. Nonlocal heat transport is also called an anomalous heat transport. In order to explain nonlocal heat transport, lots of theoretical models have been developed such as fractional diffusion models and two-field critical gradient models, but both magnetic shear and toroidal curvature effects were not considered in those models. As known, magnetic shear plays a more important role in the whole process of turbulence development (excitation - - >linear growth - - >quasi-linear and nonlinear development - - > nonlinear saturation),while velocity shear roles only at the nonlinear saturation state. Thus, it is motivated to develop a new theoretical model of nonlocal heat transport including both magnetic shear and toroidal curvature effects. At the same time, the comparisons between nonlocal heat transport events induced by cold pulse and heat pulse will be done to find some common mechanism behind them. The nonlocal electron heat transport experiments at both HL-2A and other tokamaks will also be explained and numerically studied with our theoretical model.

近十多年来，在国内外一些中、大型托卡马克装置上的边缘调制实验中，都观察到一些非局域电子热输运的现象：例如在边缘等离子体注入杂质、弹丸或超声分子束等引起边缘电子温度降低的瞬间，芯部电子温度却突然升高的现象；边缘电子回旋共振加热、中性束注入等引起瞬间芯部电子温度和全空间电子温度同时升高的现象。这些非局域热输运现象的时间尺度远小于局域热输运所遵循的回旋玻姆定标律的热扩散时间尺度，被认为是一种反常电子热输运。为了解释这些实验现象，人们提出了若干理论模型；但它们都未包含磁剪切和磁环形曲率效应。本项目拟建立一个包含这两个效应的非局域电子热输运模型，来数值模拟研究这种输运过程，并着重考察这两个效应在该输运过程中的作用。与此同时，对比研究冷脉冲和热脉冲所分别引起的非局域热输运现象，寻找其中共同的物理机制；并模拟HL-2A上已有的和即将开展的非局域输运实验和分析国内外一些托卡马克装置上的相关实验结果。

近十多年来，在国内外一些中、大型托卡马克装置上的边缘调制实验中，都观察到一些非局域电子热输运的现象：例如在边缘等离子体注入杂质、弹丸或超声分子束等（冷脉冲）引起边缘电子温度降低的瞬间，芯部电子温度却突然升高的现象；边缘电子回旋共振加热等（热脉冲）引起瞬间芯部电子温度和全空间电子温度同时升高的现象。这些非局域热输运现象被认为是一种反常电子热输运。为了解释这些实验现象，人们提出了若干理论模型；但它们都未包含磁剪切和磁环形曲率效应。本项目综合对比研究了磁剪切和磁环形曲率效应在冷脉冲和热脉冲所分别引起的非局域热输运过程中的作用，并取得了一些重要的进展和突破：.（1）在理论模拟方面：建立了一个含有磁剪切效应和磁环形曲率效应的双场自组织临界（SOC）非局域输运理论模型，研究了磁剪切对反常电子热输运和改善约束的作用；并对SOC模型进行改进，建立了多场非局域输运理论模型，进一步考虑了离子温度梯度（ITG）湍流和捕获电子模（TEM）湍流输运，添加了湍流强度增长对密度梯度的依赖关系和磁剪切效应；建立了一个新的三维输运理论模型来模拟三维冷脉冲超声分子束注入（SMBI）或喷气（GP）以及热脉冲电子回旋共振加热（ECRH）注入，并开发了相应的大型并行trans-neut程序代码；综合数值模拟对比了冷热脉冲注入所引起的非局域输运现象，并发现了这两种非局域输运现象的一些共同特征。.（2）在实验方面：在HL-2A上研究了冷脉冲引起的非局域输运过程中的自组织临界特性、雪崩现象、磁扰动抑制现象、湍流强度及极向流剪切的变化等；在HL-2A上同时对比研究了冷脉冲和ECRH加热引起的热脉冲非局域输运现象；在J-TEXT托卡马克装置上发现外加共振磁扰动（RMP）更够有效地增强非局域输运现象。.（3）在模拟与实验对照方面：对比研究了反磁剪切与内部输运垒的作用，并讨论了磁环形曲率对反常输运系数的作用；对比研究了冷脉冲引起的非局域热输运以冲击波前向内传播过程中的自组织临界（SOC）现象；在真实磁场HL-2A托卡马克磁场位形下，采用真实的实验诊断剖面和参数，数值模拟与实验对照研究了冷脉冲超声分子束注入引起的等离子体输运及平衡剖面的演化，发现二者吻合得较好。.这些研究结果不仅有助于理解非局域输运过程，而且对于降低反常输运，实现聚变等离子体的高约束性能具有重要意义。

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