Experimental observation and investigation of fluctuation-induced inward transport in HL-2A NBI heated L-mode plasma

doi:10.16568/j.0254-6086.202504010

Abstract

Abstract: By employing Langmuir probe arrays at the boundary of L-mode plasma in the HL-2A device, the key parameters such as plasma density, temperature and electric potential were precisely measured. Subsequently,the characteristics of boundary fluctuation-induced particle transport were calculated, and their spectral features and the reversal law of fluctuation-induced transport direction were thoroughly analyzed using frequency-domain decomposition techniques. The research reveals that local poloidal flow shear exhibits a weak correlation with inward fluctuation transport, whereas broad-spectrum low-frequency fluctuations below 40 kHz dominate theinward particle transport. The reversal of transport direction is governed by an anti-correlation in the cross-phase between density fluctuations and velocity fluctuations. Based on the frequency-temporal evolution of fluctuation transport, the transport process can be divided into two stages: in the initial stage, the amplitude of outward fluctuation transport gradually decays, while fluctuations in certain frequency bands begin to transport inward.The interaction between these components suppresses the total transport flux. As the inward transport component accumulates and eventually surpasses the outward component, the total flux reverses to inward, leading to a significant improvement in particle confinement during this stage. Further analysis indicates that the fluctuation-induced heat conduction flux exhibits an inward trend during both the suppression and reversal phases of the fluctuation particle flux. Moreover, the onset of inward heat transport lags noticeably behind the reversal time of the fluctuation particle flux. This study presents the first observation of broad-spectrum low-frequency fluctuation-induced inward transport in a toroidal magnetic confinement device, unveils the physical mechanism behind the reversal of fluctuation transport direction, and provides critical experimental support and guidance for optimizing particle confinement performance in magnetically confined plasma devices.

Key words: Fluctuation, Inward particle transport, NBI heating, Plasma

摘要： 通过在 HL-2A 装置低约束模等离子体边界布设朗缪尔探针阵列，精确测量等离子体密度、温度、电势等关键参数，进而计算边界涨落引起的粒子输运特性，并借助频域分解技术深入剖析了其频谱特征与输运方向转变规律。研究发现，局域极向流剪切与涨落向内输运关联性较弱，而 40 kHz 以下低频宽谱涨落在粒子向内输运中占据主导地位，其输运方向的改变受控于密度涨落与速度涨落之间的相角反相关系。依据涨落输运的时频特征演变，可将输运过程划分为 2 个阶段：在初始阶段，向外的涨落输运幅值逐渐衰减，部分频段涨落开始向内输运，两者相互作用致使输运总通量受到抑制；随着向内输运成分不断累积并最终超越向外输运成分，输运总通量转向向内，此阶段粒子约束性能得以显著提升。进一步分析表明，涨落引起的热传导通量在涨落粒子通量受抑制及转为向内的时间段内均呈现向内趋势，且其向内输运的起始时刻相较于涨落粒子通量的向内转变时刻存在明显滞后性。该研究首次观测到了环形磁约束装置上的低频宽谱涨落引起的向内输运现象，揭示了涨落输运方向转变的物理机制，为优化磁约束等离子体装置的粒子约束性能提供了关键的实验支持与指导。

关键词: 涨落, 向内粒子输运, NBI 加热, 等离子体

CLC Number:

O533

WANG Tian-xiong, WU Jie, LAN Tao, DING Wei-xing, WU Jia-ren, XU Min, NIE Lin, LIU A-di, XIE Jin-lin, LIU Wan-dong, ZHONG Wu-lü, ZHUANG Ge. Experimental observation and investigation of fluctuation-induced inward transport in HL-2A NBI heated L-mode plasma[J]. Nuclear Fusion and Plasma Physics, 2025, 45(4): 437-445.

王天雄, 吴捷, 兰涛, 丁卫星, 邬佳仁, 许敏, 聂林, 刘阿娣, 谢锦林, 刘万东, 钟武律, 庄革 . HL-2A NBI 加热 L 模等离子体中涨落向内输运现象的实验观测与研究[J]. 核聚变与等离子体物理, 2025, 45(4): 437-445.

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