弹丸触发ELM的非线性过程研究

The international thermonuclear experimental reactor (ITER) will be operated at H-mode with type I edge localized mode (ELM) due to the good energy and particle confinement. In recent years, many ELM mitigation experiments on the tokamaks around the world are implemented aiming at solving problem that the energy loss during ELM crash in ITER is too large for the diverter to take. The experiment results show that the energy loss of single ELM crash can be reduced by high repetition rate pellet injection. Therefore, it is necessary to develop a self consistent model of ELM crash triggered by pellet injection, and this model would include many physics processes, such as: the ablation of solid pellet due to thermal electron heat-flux, the expansion and ionization of the pellet ablation cloud, the ELM crash triggered by peeling-ballooning (PB) mode turbulence and so on. The module describing ELM triggered by pellet injection will be constructed using BOUT++ code. During the simulation of ELM triggered by pellet injection, the perturbation of plasma parameters, such as density, temperature, current density and so on, will be monitored to revel the role of pellet ablation in this process, and the affection of the pellet size, depth of injection and other pellet parameters on the PB mode growth rate and ELM crash will be discussed together with the experiment results on HL-2A. The research results will be useful with regard to controlling the ELM crash on ITER.

伴随I型边缘局域模（ELM）的高约束模（H模）具备良好的粒子和能量约束，是国际热核聚变实验堆（ITER）的基本运行方案。近年来，国际国内托卡马克装置上开展了大量弹丸缓解ELM 的实验探索，以解决将来ITER装置上ELM释放能量超过偏滤器负载的问题。实验已经证实，通过重复注入弹丸可以触发高频ELM，从而降低ELM导致的粒子和能量损失。本项目基于已有实验现象拟建立一个描述弹丸触发ELM的自洽模型，描述以下物理过程：热电子轰击固体弹丸导致弹丸消融、弹丸云膨胀与电离、剥离气球模湍流触发ELM崩塌等。在BOUT++代码体系下开发相应模块并开展弹丸触发ELM的模拟，通过跟踪等离子体的温度、密度、电流等参数扰动演化过程，揭示弹丸消融在ELM非线性崩塌过程中的作用，结合HL-2A装置的实验探讨弹丸注入深度、弹丸尺寸等参数对剥离气球模增长率以及ELM崩塌的影响。研究结果有助于控制ITER装置上的ELM崩塌。

边界局域模（ELM）是高约束模（H模）聚变等离子体中边缘输运垒的周期性崩塌与重建过程，伴有I型ELM的H模是未来磁约束聚变堆ITER和CFETR装置的基本运行模式，I型ELM将导致大量的粒子和热流轰击偏滤器靶板和第一壁，因此ELM控制是关系到ITER和CFETR能否实现稳定运行的关键问题之一。本项目在BOUT++代码体系下编写了弹丸控制ELM代码，研究了弹丸触发ELM、加料缓解ELM、电阻和平衡流对ELM的影响等过程中的物理机制。研究发现不同注入位置的弹丸对ELM的缓解效果完全不同，台基中部的弹丸具有良好的ELM缓解效果；模拟了弹丸触发ELM非线性过程，发现弹丸注入可造成局部等离子体压强梯度增加，改变剥离气球模的不稳定性从而触发ELM；研究了加料缓解ELM的物理机制，通过在等离子体方程中加入源项实现了ELM缓解模拟；研究了电阻对ELM的影响，发现台基中部的电阻可增加剥离气球模的线性不稳定性，台基底部的电阻可通过抑制剥离气球模湍流减小ELM；研究了平衡平行剪切流对剥离气球模的影响，揭示了剪切流对剥离气球模线性和非线性演化中的作用。研究有助于理解现有聚变装置的ELM控制实验，也为ITER和CFETR装置上控制ELM提供物理依据。