Influence of Micro-turbulence on Neoclassical Tearing Mode Onset

Shi, Tonghui; Wei, L.; Wang, H. H.; Li, E.; Shen, B.; Qian, J. P.; Wang, Y. M.; Zhang, T.; Zhao, H. L.; Zeng, L.; Zhang, Y.; Liu, H. Q.; Ma, Q.; Chen, D. L.; Luo, Z. P.; Li, Y. Y.; Shen, Z. C.; Xu, L. Q.; Zhang, B.; Li, M. H.; Wang, Z. X.; Ling, B. L.; Gong, X. Z.; Sun, Y.; Wan, B.

doi:10.48550/arxiv.2103.15506

Cited by 3 publications

(5 citation statements)

References 27 publications

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“…This results in w c being a growing function of β ϑ at fixed ε and q. This dependence is in agreement with the recent EAST measurements of the critical island width (see figure 9) for the 2/1 NTM triggered by the resonant magnetic perturbations [31].…”

Section: Poloidal Beta Effectssupporting

confidence: 92%

“…see figure 2(c). δ also enters equation ( 29) which, in turn, influences the radial shift of drift islands for passing particles in equation (31). As can be seen from Figure 2(b), ωD increases 10 The parameter ∂rR 0 written in terms of β ϑ and li is derived in [27] for large aspect ratios.…”

Section: Triangularity Effectsmentioning

confidence: 94%

“…The effect associated with the finite β on this radial shift is weaker as β also appears implicitly in equation ( 29) via L−1 B . As can be seen from equation (31), the drift island separatrix position also depends on B ϑ , which makes drift islands wider for stronger B ϑ , e.g. see figure 1.…”

Section: Drift Magnetic Islands Rdk-ntm Formulationmentioning

confidence: 99%

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Drift kinetic theory of the NTM magnetic islands in a finite beta general geometry tokamak plasma

et al. 2022

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In [K Imada et al. Nucl. Fusion 59 (2019) 046016] a new 4D drift kinetic nonlinear theory, valid in the limit of a low beta, small inverse aspect ratio, circular cross section, toroidal geometry, to describe the plasma response to the neoclassical tearing mode (NTM) magnetic perturbation is derived. In [A V Dudkovskaia et al. Plasma Phys. Control. Fusion 63 (2021) 054001] this theory is reduced in a low collisionality limit, which allows a dimensionality reduction to a 3D problem to efficiently resolve the collisional dissipation layer in the vicinity of the trapped-passing boundary. [A V Dudkovskaia et al. Plasma Phys. Control. Fusion 63 (2021) 054001] adopts an improved model for the magnetic drift frequency, which reduces the threshold magnetic island half-width from $8.73 \rho_{b i}$, where $\rho_{b i}$ is the trapped ion banana orbit width, to $1.46 \rho_{b i}$, making it in a closer agreement with experimental observations for the large aspect ratio tokamak equilibrium. In the present paper, the theory is extended to a high beta, arbitrary tokamak geometry to capture the plasma shaping effects on the NTM threshold physics with the focus on the non-zero triangularity discharges that are known to have a strong impact on the plasma MHD stability. First, it is found that the higher triangularity plasma is more prone to NTMs which is in agreement with the $2/1$ tearing mode onset relative frequency measurements in DIII-D. Second, the NTM threshold dependence on the tokamak inverse aspect ratio obtained in [A V Dudkovskaia et al. Plasma Phys. Control. Fusion 63 (2021) 054001] is refined and extended to a finite aspect ratio limit. Third, the NTM threshold dependence on poloidal beta is obtained and benchmarked against the EAST threshold island width measurements.

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Section: Poloidal Beta Effectssupporting

confidence: 92%

Section: Triangularity Effectsmentioning

confidence: 94%

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Drift kinetic theory of the NTM magnetic islands in a finite beta general geometry tokamak plasma

et al. 2022

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“…For a detailed description of the Miller parametrisation process, see appendix C of [38]. The EAST experimental equilibrium reconstruction is based on the EAST discharge number 91972 (5300 ms) [21,39]. The KSTAR experimental equilibrium reconstruction is based on the KSTAR discharge number 32129 (2300 ms).…”

Section: Threshold Island Widthmentioning

confidence: 99%

Drift kinetic theory of neoclassical tearing modes in tokamak plasmas: polarisation current and its effect on magnetic island threshold physics

Dudkovskaia,

Connor,

Dickinson

et al. 2023

Nucl. Fusion

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A nonlinear 4-dimensional drift island theory derived in [K Imada et al. Nucl. Fusion 59 (2019) 046016 and references therein] provides qualitative predictions of the plasma response to a stationary neoclassical tearing mode (NTM) magnetic island in a low beta, large aspect ratio tokamak plasma. [A V Dudkovskaia et al. Plasma Phys. Control. Fusion 63 (2021) 054001] refines a model for the magnetic drift frequency and exploits the limit of rare collisions, reducing this theory to 3-dimensional and thus providing a more accurate treatment of the trapped-passing boundary layer. The drift island theory is further improved in [A V Dudkovskaia et al. Nucl. Fusion 63 (2023) 016020] by introducing plasma shaping and finite beta effects. In the present paper, an improved model is adopted to resolve the drift island separatrix boundary layer, allowing one to investigate the polarisation current contribution that exists around the magnetic island separatrix, including in the presence of the background electric field. In particular, different magnetic topologies from both sides of the separatrix generate a radial discontinuity in the distribution function gradient there, when collisions are neglected. Allowing for collisional dissipation in the leading order distribution function around the separatrix resolves this discontinuity, smoothing the density distribution. The overall effect of the polarisation current on the NTM threshold is then combined from the outer contributions that exist outside the layer, as well as the separatrix layer piece, and self-consistently accounts for the electrostatic potential reconstructed from plasma quasi-neutrality. The corresponding NTM threshold is quantified and compared with previous predictions of [A V Dudkovskaia et al. Plasma Phys. Control. Fusion 63 (2021) 054001, A V Dudkovskaia et al. Nucl. Fusion 63 (2023) 016020].

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“…Instead, we are interested in the NTM onset and would like to provide data or enlightening observations since we recently installed a 2D gas electron multiplier (GEM) camera at EAST [24,25]. The RMP coils are preset with an n = 1 fixed phase difference, the same current ramping rate, and the same switch-on and switch-off times [26]. This means that the RMP provides a consistent error field source.…”

Section: Introductionmentioning

confidence: 99%

Observation of neoclassical tearing-mode excitation in EAST low-β _p H-mode plasmas using a gas electron multiplier-based camera

Qu¹,

Li²,

Xu³

et al. 2022

Nucl. Fusion

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The excitation of an initially stable neoclassical tearing mode (NTM) is investigated in Experimental Advanced Superconducting Tokamak (EAST) low-β p H-mode plasmas (β p is defined as the ratio of the thermal pressure to the poloidal magnetic pressure). Using similar plasma parameters, n = 1 resonant magnetic perturbation (RMP) cannot always successfully excite the m/n = 2/1 NTM with the same RMP coil current setup (n and m are the toroidal and poloidal mode numbers, respectively). Data from a gas electron multiplier camera shows that NTM destabilization is related to RMP-induced crashes at the q = 1 resonant surface during the RMP ramp-up phase. The second RMP-induced crash amplitude decays exponentially as β p increases. There is a critical value β p ≈ 0.76 above which the crash amplitude (or seed island width) is too small (below the critical island width) to trigger an NTM. Observation and analysis indicate that the m/n = 2/1 NTM is not forcibly driven by the n = 1 RMP (such as the m/n = 2/1 component), but is probably due to electron heat transport between the q = 1 and the q = 2 resonant surfaces. This paper describes experimental observations of NTM excitation which also have implications for further investigations of NTM locking and disruptions.

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Influence of Micro-turbulence on Neoclassical Tearing Mode Onset

Cited by 3 publications

References 27 publications

Drift kinetic theory of the NTM magnetic islands in a finite beta general geometry tokamak plasma

Drift kinetic theory of the NTM magnetic islands in a finite beta general geometry tokamak plasma

Drift kinetic theory of neoclassical tearing modes in tokamak plasmas: polarisation current and its effect on magnetic island threshold physics

Observation of neoclassical tearing-mode excitation in EAST low-β _p H-mode plasmas using a gas electron multiplier-based camera

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Influence of Micro-turbulence on Neoclassical Tearing Mode Onset

Cited by 3 publications

References 27 publications

Drift kinetic theory of the NTM magnetic islands in a finite beta general geometry tokamak plasma

Drift kinetic theory of the NTM magnetic islands in a finite beta general geometry tokamak plasma

Drift kinetic theory of neoclassical tearing modes in tokamak plasmas: polarisation current and its effect on magnetic island threshold physics

Observation of neoclassical tearing-mode excitation in EAST low-β p H-mode plasmas using a gas electron multiplier-based camera

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Observation of neoclassical tearing-mode excitation in EAST low-β _p H-mode plasmas using a gas electron multiplier-based camera