Investigation of the critical edge ion heat flux for L-H transitions in Alcator C-Mod and its dependence on B_T

This paper presents investigations on the role of the edge ion heat flux for transitions from L-mode to H-mode in Alcator C-Mod. Previous results from the ASDEX Upgrade tokamak indicated that a critical value of edge ion heat flux per particle is needed for the transition. Analysis of C-Mod data confirms this result. The edge ion heat flux is indeed found to increase linearly with density at given magnetic field and plasma current. Furthermore, the Alcator C-Mod data indicate that the edge ion heat flux at the L-H transition also increases with magnetic field. Combining the data from Alcator C-Mod and ASDEX Upgrade yields a general expression for the edge ion heat flux at the L-H transition. These results are discussed from the point of view of the possible physics mechanism of the L-H transition. They are also compared to the L-H power threshold scaling and an extrapolation for ITER is given.本文针对阿尔卡特C-Mod（Alcator C-Mod）托卡马克装置中，低约束模（L-mode）向高约束模（H-mode）转换过程的边缘离子热通量作用展开了研究。此前阿斯德克斯升级（ASDEX Upgrade）托卡马克的研究结果表明，实现该转换需要满足单位粒子边缘离子热通量的临界阈值条件。对阿尔卡特C-Mod实验数据的分析验证了这一结论：在给定磁场与等离子体电流的条件下，边缘离子热通量确实随粒子密度呈线性增长。此外，阿尔卡特C-Mod的实验数据还显示，L-H转换时刻的边缘离子热通量同样随磁场强度升高而增大。整合阿尔卡特C-Mod与阿斯德克斯升级托卡马克的实验数据，可推导出L-H转换时刻边缘离子热通量的通用表达式。本文从L-H转换的潜在物理机制视角对上述结果进行了讨论，并将其与L-H功率阈值定标关系进行对比，同时给出了针对国际热核聚变实验堆（ITER）的外推结果。