The dynamics of a neoclassical tearing mode (NTM) influenced by energetic ions on EAST

Li, Erzhong; Igochine, V.; Xu, Long; Shi, Tonghui; Zhao, Hailin; Liu, Yong; Ti, Ang; White, R. B.; Zhang, J; Zhu, Y. B.; Huang, J.; Shen, Biao; Lin, Shiyao; Qian, J.; Gong, Xianzu; Hu, Liqun; Contributors, East

doi:10.1088/0741-3335/58/4/045012

Cited by 14 publications

(11 citation statements)

References 54 publications

(73 reference statements)

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“…The experiments are generated by the torque-balanced injection of co-and counter-current neutral beams on EAST, motivated by the previous experiments where only the co-current neutral beam injection (NBI) was applied (as seen in [18]). The counter-current injection of NBI leads to a very slow rotation of plasma near the mode natural frequency.…”

Section: Methodsmentioning

confidence: 99%

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The spontaneous destabilization of neoclassical tearing mode with existing energetic ions in low torque tokamak plasmas

Zhao

et al. 2017

Nucl. Fusion

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Periodic destabilization of a neoclassical tearing mode (NTM, m/n = 2/1) in between two edge localized modes (ELMs) is observed with a varying frequency that deviates from the wave-particle resonance determined precession frequency, is instead near the electron diamagnetic drift frequency. This scenario is created by the balanced injection of co- and counter-current neutral beams which give rise to low-torque plasmas with a high confinement on the experimental advanced superconducting tokamak (EAST). The destabilization is obviously dependent on the ratio of the mode frequency to the electron diamagnetic frequency, indicating the effect of relative rotation between the NTM and plasmas on the mode stability. In particular, the role of polarization current in general Rutherford equation is identified by experimental data reported in this letter.

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Section: Methodsmentioning

confidence: 99%

“…More specifically, the dispersion relationship for mode stability has been determined in [17]. Experiments have showed the effect of ion polarization current on the evolution of a neoclassical island [18]. However, its influence on the onset of NTM was undetermined in those experiments.…”

Section: Introductionmentioning

confidence: 99%

The spontaneous destabilization of neoclassical tearing mode with existing energetic ions in low torque tokamak plasmas

Zhao

et al. 2017

Nucl. Fusion

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“…A recent theoretical paper suggests that fast ions can significantly affect the non-linear evolution of (N)TMs through an uncompensated cross-field current associated with fast-ion orbit effects; the predicted effect is most significant in plasmas with weak magnetic shear [22]. Experimentally, rapid frequency chirping of (N)TMs has been observed on TFTR [23], ASDEX-Upgrade [24,25], EAST [26], and HL-2A [27] in the presence of fast ions. Frequency chirping often indicates that there is a strong resonant interaction between fast ions and the modes.…”

Section: Introductionmentioning

confidence: 99%

Cause and impact of low-frequency chirping modes in DIII-D hybrid discharges

et al. 2020

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Significant variations in MHD activity and fast-ion transport are observed in the DIII-D high-beta, steady-state hybrid discharges with a mixture of electron cyclotron (EC) waves and neutral beam injection (NBI). When electron cyclotron heating (ECH) or current drive (ECCD) is applied, Alfvén eigenmodes (AEs) are usually suppressed and replaced by low-frequency bursting modes. The analysis of a recently compiled database of hybrid discharges suggests that the change of the fast-ion pressure especially the perpendicular pressure is the main factor responsible for the instability transition although the transition in some discharges can also be explained by a slight drop of the safety factor . The lower ratio of fast-ion injection speed vinj to Alfvén speed valfven and slight drop of during ECCD also facilitate the transition. The database shows that AEs mainly occur when the fast-ion fraction is less than 0.53 and is greater than 0.50, while low-frequency bursting modes appear in the opposite regime. Here, Pf and Ptotal are the central fast-ion pressure from classical prediction and total plasma pressure, respectively. The correlation with is weaker, and is around unity in all the cases. The reason why the instability transition correlates with and is that they can significantly modify the drive of low-frequency bursting modes and AEs. The explanation is supported by the observation that low-frequency bursting modes are rarely seen in the hybrids with NBI only, with EC waves and counter-NBI, or with high plasma density. A careful check of the low-frequency bursting modes suggests that they are mainly chirping (neoclassical) tearing modes (referred to as chirping (N)TMs), i.e. the mode frequency firstly jumps up from the steady (N)TM frequency, then chirps down, and finally returns to the steady (N)TM frequency. Occasionally, the (N)TMs are fully stabilized and replaced with pure fishbones. The resonance condition calculation and ‘Kick’ model simulations suggest that (N)TMs and fishbones can interact through modification of the fast ion distribution in phase space, which influences the drive.

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“…In both ASDEX Upgrade [16] and TFTR [17], TMs were observed to chirp several kHz in frequency. In EAST, small oscillations in mode frequency are attributed to interaction with fast ions [18]. In the reversed-field pinch, neutral-beam injection reduced the amplitude of (m, n) = (1,5) tearing modes 60% [19].…”

Section: Introductionmentioning

confidence: 99%

The phase-space dependence of fast-ion interaction with tearing modes

et al. 2018

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Modulation of various neutral beam sources probes the interaction of fast ions with tearing modes (TM) in the DIII-D tokamak. As measured by electron cyclotron emission, the tearing modes have an island width of ∼8 cm and change phase at the q = 2 surface. (Here, m is the poloidal mode number and n is the toroidal mode number.) Deuterium neutral beam injection by six sources with differing injection geometries produces the fast ions. To study the interaction in different parts of phase space, on successive discharges, one of the six sources is modulated at 20 Hz to populate different fast-ion orbits. The modulation only changes the island width by a few millimeters, implying that any fast-ion effect on mode stability is below detection limits. When compared to the expected signals in the absence of TM-induced transport, both the average and modulated neutron signals deviate, implying that fast-ion transport occurs in much of phase space. Fast-ion Dα (FIDA) measurements detect reductions in signal at wavelengths that are sensitive to counter-passing ions. Neutral particle analyzer data imply poor confinement of trapped fast ions. Calculations of the expected fast-ion transport that use measured TM properties successfully reproduce the data.

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The dynamics of a neoclassical tearing mode (NTM) influenced by energetic ions on EAST

Cited by 14 publications

References 54 publications

The spontaneous destabilization of neoclassical tearing mode with existing energetic ions in low torque tokamak plasmas

The spontaneous destabilization of neoclassical tearing mode with existing energetic ions in low torque tokamak plasmas

Cause and impact of low-frequency chirping modes in DIII-D hybrid discharges

The phase-space dependence of fast-ion interaction with tearing modes

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