We report here on the discovery on NSTX-U of a qualitatively new type of non-thermal emission from plasmas in the ion-cyclotron frequency range (ICE). This new type of ICE is weakly damped, γdamp/ωICE ≈ 0.14%, low order eigenmodes, excited by a fast ion population radially located near an internal transport barrier. The ICE appears as repetitive bursts with durations of ≈1 ms, and the bursts exhibit frequency chirps upwards and/or downwards with maximum δf/f ≈ 1%. We refer to this chirping ICE as ch-ICE. The bursts are longer than the typical ICE bursts of ≈100 μs reported previously for NSTX and NSTX-U, for simplicity, NSTX(-U). The chirping resembles that seen in modeling of weakly unstable fast particle driven instabilities (cf, Berk et al 1997 Phys. Lett. A 234 213). These data also provide some preliminary indications of non-linear coupling between the ch-ICE harmonics. Despite extensive experimental and theoretical studies of ICE, theoretical understanding of ICE remains qualitative at best. The detailed experimental observations of ICE from NSTX(-U) find a wide variation in the ICE characteristics. The new observations of ch-ICE presented here, combined with the characteristics of ICE on NSTX(-U) previously reported (Fredrickson et al 2019 Phys. Plasmas26 032111), could guide the development of more complete theoretical models of ICE.
我们在此报告在NSTX-U上发现的一种定性上全新的、来自等离子体的离子回旋频率范围（ICE）非热辐射类型。这种新型ICE是弱阻尼的，γ_阻尼/ω_ICE ≈ 0.14%，低阶本征模，由位于内部输运垒附近的快离子群体激发。该ICE表现为重复性爆发，持续时间约为1毫秒，且爆发呈现向上和/或向下的频率啁啾，最大δf/f ≈ 1%。我们将这种啁啾ICE称为ch-ICE。这些爆发比先前在NSTX和NSTX-U上报道的典型ICE爆发（约100微秒）持续时间更长，为简洁起见，记为NSTX(-U)。这种啁啾现象与弱不稳定快粒子驱动模式建模中观察到的现象相似（参见Berk等人，1997，Phys. Lett. A 234, 213）。这些数据还初步表明ch-ICE谐波之间存在非线性耦合。尽管对ICE已有广泛的实验和理论研究，但对其理论理解仍主要停留在定性层面。来自NSTX(-U)的详细实验观测揭示了ICE特性的广泛变化。本文呈现的ch-ICE新观测结果，结合先前报道的NSTX(-U)上ICE特性（Fredrickson等人，2019，Phys. Plasmas 26, 032111），可为发展更完整的ICE理论模型提供指导。