Non-resonant fishbone-like modes in tokamak plasmas with reversed magnetic shear

Wang, Xianqu; Wang, Xiaogang

doi:10.1088/0029-5515/56/3/036024

Cited by 8 publications

(4 citation statements)

References 35 publications

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“…the rotation frequency of the m/n = 2/1 magnetic islands is locked gradually. The radial magnetic component δB r and spatial phase angle φ 0 for the LMs are measured by the saddle loops, as shown in figure 2(e), which can be expressed as in [32]: δB r = B r0 • cos(nφ − φ 0 ), where eight magnetic loops are located in the lower field side (LFS) of the equatorial plane along the toroidal direction φ. The n = 1 magnetic island is locked by the tungsten protector limiter (−0.4π φ Lim −0.3π) for t 3.66 s, and the 3D intrinsic error fields are formed accordingly.…”

Section: Mode Lockingmentioning

confidence: 99%

Influence of low-Z impurity on the stabilization of m/n = 2/1 tearing/locked modes in EAST

Xu¹,

Liang²,

Lai³

et al. 2022

Nucl. Fusion

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The impact of the low-Z impurity concentration on the modes stabilization has been investigated in the EAST tokamak. Series of tearing modes (TMs) with multiple helicities are excited by the concentration of low-Z (carbon) impurity, and the dominant mode structure is featured by m/n = 2/1 magnetic islands that propagate in electron diamagnetic drift direction (m and n are poloidal and toroidal mode numbers respectively). The m/n = 2/1 locked modes (LMs) can be formed by the redistribution of low-Z impurity concentration, which is unlocked spontaneously for the decreasing of impurity concentration, where the width of magnetic islands can reach w ≅ 5 cm (w/a ≅ 0.1, a is minor radius). The increasing of electromagnetic brake torque is the primary reason for the mode locking, and the 'O'-point of m/n = 2/1 magnetic islands is locked by the tungsten protector limiter (toroidal position: -0.4π ≦ φ ≦ -0.3π) with separation of Δφ ≅ 0. The 3D asymmetric structure of m/n = 2/1 magnetic islands is formed for the interaction with the tungsten protector limiter, and the electromagnetic interaction decreases dramatically for the separation of Δφ ≧ 0.2π. The mechanisms for the mode excitation and locking can be illustrated by the "hysteresis effect" between the low-Z impurity concentration and the width of m/n = 2/1 magnetic islands, namely the growth of magnetic islands is modulated by the low-Z impurity concentration, and the rotation velocity is decelerated accordingly. However, the intrinsic mechanism for the unlocking of m/n = 2/1 LMs is complicated by considering the concentration of the low-Z impurity, and the possible unlocking mechanism is discussed. Therefore, understanding of the relationship between the impurities and magnetic islands is more important for optimizing the control techniques (RMP→LMs, ECRH→NTM, impurity seeding→major collapse, et al).

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Section: Mode Lockingmentioning

confidence: 99%

Influence of low-Z impurity on the stabilization of m/n = 2/1 tearing/locked modes in EAST

Xu¹,

Liang²,

Lai³

et al. 2022

Nucl. Fusion

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“…This is the case for the ITER scenario considered in the present work. We note that this is different from the off-axis FB [25][26][27] (also called FB-like mode) where the dominant component has the poloidal mode number larger than 1.…”

Section: Introductionmentioning

confidence: 59%

Resistive wall mode and fishbone mode in ITER steady state scenario: roles of fusion-born alphas and plasma flow

He,

Liu,

Hao

et al. 2024

Nucl. Fusion

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Drift-kinetic effects of fusion-born alpha particles on the n=1 (n is the toroidal mode number) resistive wall mode (RWM) is numerically investigated for a recent design of the ITER 10 MA steady state plasma scenario, utilizing a magneto-hydrodynamic (MHD)-kinetic hybrid toroidal model. While the fluid theory predicts unstable RWM as the normalized plasma pressure βN exceeds the no-wall Troyon limit and with the mode growth rate monotonically increasing with βN, inclusion of the drift-kinetic contribution of trapped alphas qualitatively modifies the behavior by stabilizing the mode at high βN. In fact, a complete stabilization of the n=1 RWM up to the ideal-wall Troyon limit is found. On the other hand, another unstable branch - the alpha-driven n=1 fishbone mode (FB) – is identified in the high-βN regime, with the mode frequency matching that of the toroidal precession frequency of trapped alphas. Fast plasma toroidal flow however helps mitigate the FB instability. Kinetic stabilization of the RWM and flow stabilization of the (alpha-triggered) FB result in an enhancement of βN from the design value of 3.22 to 3.52 for the ITER scenario considered, while still maintaining stable plasma operation against the aforementioned MHD instabilities.

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“…In these tokamak devices, the modes can lead to large fast ion transport and the formation of internal transport barrier, which result in broadening the distribution of the fast ions. Based on these relative experiment results, the physical mechanisms of the non-resonant EPM have been also numerically investigated in previous works [31][32][33]. For the equilibrium and the stability of the non-resonant EPMs, Wang et al found the experimental level of plasma rotation hardly has any impact on them.…”

Section: Introductionmentioning

confidence: 97%

Simulation of non-resonant high-order harmonics energetic particle modes in tokamak plasmas

Liu,

Ren,

Yang

et al. 2024

Phys. Scr.

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Based on the parameters of the HL-2A experiment, the effect of energetic particles (EPs) on non-resonant high-order harmonics energetic particle modes (EPMs) with qmin>1 is investigated in the present work. Hybrid kinetic-magnetohydrodynamic nonlinear code M3D-K is performed to simulate the linear properties and the nonlinear evolution of the non-resonant EPM during neutral beam injection (NBI). To deeply understand the physical mechanism of interaction resonant between energetic-ions and non-resonant EPM, this work compares the effects of passing energetic particles and trapped energetic particles on the non-resonant EPM instabilities. It is numerically identified that EPs’ effects on high n harmonics (m/n = 2/2, 3/3, 4/4) instability are more obvious than the m/n = 1/1 mode. Furthermore, the effects of energetic particles injection energy, the minimum safety factor qmin , toroidal rotation and beam ion distribution on the features of high n harmonics are also investigated specifically. Toroidal rotation is found to suppress high n harmonics, which is more obvious for the modes driven by trapped particles. Nonlinear simulation results show that these non-resonant high n harmonics can induce larger energetic ion transport, which may affect the plasma confinement performance.

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Non-resonant fishbone-like modes in tokamak plasmas with reversed magnetic shear

Cited by 8 publications

References 35 publications

Influence of low-Z impurity on the stabilization of m/n = 2/1 tearing/locked modes in EAST

Influence of low-Z impurity on the stabilization of m/n = 2/1 tearing/locked modes in EAST

Resistive wall mode and fishbone mode in ITER steady state scenario: roles of fusion-born alphas and plasma flow

Simulation of non-resonant high-order harmonics energetic particle modes in tokamak plasmas

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