Transition characteristics, fluctuation evolution, and the role of coherent mode in electron cyclotron resonance heated low to high mode transition in KSTAR

IF 2 3区 物理与天体物理 Q3 PHYSICS, FLUIDS & PLASMAS Physics of Plasmas Pub Date : 2024-09-05 DOI:10.1063/5.0225207
Hogun Jhang, Minjun J Choi, Hyun-Seok Kim
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Abstract

An experimental study is conducted on macro- and microscopic characteristics of low to high (LH) transition acquired by electron cyclotron resonance heating (ECRH) in KSTAR. A scan of pre-transition density demonstrates the existence of the characteristic minimum density, which requires minimum power to make LH transition. The minimum density in KSTAR shows a tendency to be lower than that evaluated from an empirical scaling law proposed by Ryter et al. [Nucl. Fusion 54, 083003 (2014)]. A comprehensive study of the evolution of low wavenumber electron temperature fluctuations is carried out using electron cyclotron emission imaging diagnostics. An analysis of the fluctuation amplitude in L-mode in terms of the electron collisionality and the electron temperature scaling length suggests that the dissipative trapped electron mode is likely to be a dominant instability before the LH transition. The fluctuation amplitude reduces first as the transition starts. A coherent mode that chirps down from 60 to 20 kHz emerges when the transition further develops. This coherent mode is then shown to revive turbulence that has been reduced significantly during the initial stage of the LH transition. The revival of turbulence could be a possible origin of the absence of the large edge localized mode when the coherent mode is persistent in ECRH-induced H-mode plasmas.
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KSTAR 中电子回旋共振加热低模向高模转变的转变特性、波动演变和相干模式的作用
通过在 KSTAR 中进行电子回旋共振加热(ECRH),对低到高(LH)转变的宏观和微观特征进行了实验研究。对转变前密度的扫描表明存在着特征性的最小密度,它需要最小的功率来实现 LH 转变。KSTAR 中的最小密度显示出低于 Ryter 等人提出的经验缩放定律[Nucl. Fusion 54, 083003 (2014)]评估值的趋势。利用电子回旋发射成像诊断技术,对低频数电子温度波动的演变进行了全面研究。根据电子碰撞性和电子温度缩放长度对 L 模式的波动幅度进行的分析表明,耗散被困电子模式很可能是 LH 转变前的主要不稳定性。随着转变的开始,波动幅度首先减小。当转变进一步发展时,出现了一个相干模式,其频率从 60 kHz 下降到 20 kHz。这种相干模式可使在 LH 过渡初期显著减弱的湍流恢复。当相干模式在 ECRH 诱导的 H 模式等离子体中持续存在时,湍流的恢复可能是大边缘局域模式缺失的一个原因。
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来源期刊
Physics of Plasmas
Physics of Plasmas 物理-物理:流体与等离子体
CiteScore
4.10
自引率
22.70%
发文量
653
审稿时长
2.5 months
期刊介绍: Physics of Plasmas (PoP), published by AIP Publishing in cooperation with the APS Division of Plasma Physics, is committed to the publication of original research in all areas of experimental and theoretical plasma physics. PoP publishes comprehensive and in-depth review manuscripts covering important areas of study and Special Topics highlighting new and cutting-edge developments in plasma physics. Every year a special issue publishes the invited and review papers from the most recent meeting of the APS Division of Plasma Physics. PoP covers a broad range of important research in this dynamic field, including: -Basic plasma phenomena, waves, instabilities -Nonlinear phenomena, turbulence, transport -Magnetically confined plasmas, heating, confinement -Inertially confined plasmas, high-energy density plasma science, warm dense matter -Ionospheric, solar-system, and astrophysical plasmas -Lasers, particle beams, accelerators, radiation generation -Radiation emission, absorption, and transport -Low-temperature plasmas, plasma applications, plasma sources, sheaths -Dusty plasmas
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