近日，美国通用原子公司的S. Ding及其研究团队取得一项新进展。经过不懈努力，他们发现一种实现聚变能的高密度高约束托卡马克等离子体状态。相关研究成果已于2024年4月24日在国际权威学术期刊《自然》上发表。
该研究团队成功演示了稳定的托卡马克等离子体，其线平均密度比格林沃尔德密度高出约20%，能量约束质量比标准高约束模式提升约50%。这一突破是通过在高极向-β场景下，利用高密度梯度对湍流输运的强化抑制实现的。实验结果显示，该运行状态具有极低的边缘瞬态扰动，同时实现了高归一化密度和约束核心的积分。这一发现支持了众多聚变反应堆设计的核心要求，为实现经济可行的聚变能源开辟了新的潜在途径。这一稳定的托卡马克等离子体状态证明了其同时具有高等离子体密度和高能量约束质量的优势，对于聚变反应堆的发展具有重要意义。。
据悉，托卡马克方法，即利用环形磁场结构来约束热等离子体，是开发利用核聚变产生电能的反应堆得最有前途的设计之一。为了达到反应堆经济性的目标，大多数托卡马克反应堆设计同时需要达到等离子体线平均密度高于经验极限——即所谓的格林沃尔德密度——并获得比标准高约束模式更好的能量约束质量。然而，这种运行状态从未在实验中得到验证。此外，高约束模式的一个长期挑战是高性能核心之间的兼容性和避免大的瞬态边缘扰动，这些扰动可能导致托卡马克中面向离子体组件承受极高热负荷。
附：英文原文
Title: A high-density and high-confinement tokamak plasma regime for fusion energy
Author: Ding, S., Garofalo, A. M., Wang, H. Q., Weisberg, D. B., Li, Z. Y., Jian, X., Eldon, D., Victor, B. S., Marinoni, A., Hu, Q. M., Carvalho, I. S., Odstril, T., Wang, L., Hyatt, A. W., Osborne, T. H., Gong, X. Z., Qian, J. P., Huang, J., McClenaghan, J., Holcomb, C. T., Hanson, J. M.
Issue&Volume: 2024-04-24
Abstract: The tokamak approach, utilizing a toroidal magnetic field configuration to confine a hot plasma, is one of the most promising designs for developing reactors that can exploit nuclear fusion to generate electrical energy. To reach the goal of an economical reactor, most tokamak reactor designs simultaneously require reaching a plasma line-averaged density above an empirical limit—the so-called Greenwald density—and attaining an energy confinement quality better than the standard high-confinement mode. However, such an operating regime has never been verified in experiments. In addition, a long-standing challenge in the high-confinement mode has been the compatibility between a high-performance core and avoiding large, transient edge perturbations that can cause very high heat loads on the plasma-facing-components in tokamaks. Here we report the demonstration of stable tokamak plasmas with a line-averaged density approximately 20% above the Greenwald density and an energy confinement quality of approximately 50% better than the standard high-confinement mode, which was realized by taking advantage of the enhanced suppression of turbulent transport granted by high density-gradients in the high-poloidal-beta scenario. Furthermore, our experimental results show an integration of very low edge transient perturbations with the high normalized density and confinement core. The operating regime we report supports some critical requirements in many fusion reactor designs all over the world and opens a potential avenue to an operating point for producing economically attractive fusion energy. A stable tokamak plasma has been demonstrated with a high plasma density and a high energy confinement quality, both of which are simultaneously important for fusion reactors.
DOI: 10.1038/s41586-024-07313-3
