Alfvénic ion temperature gradient activities in a weak magnetic shear plasma

Chen, W.; R., R.; Li, Y. Y.; Shi, Z.B.; Du, Huarong; Jiang, M.; Yu, Liming; Yuan, B.S.; Li, Y. G.; Yang, Z.C.; Shi, P.W.; Ding, X.T.; Dong, J. Q.; Wang, Z. X.; Liu, Yi; Xu, M.; Xu, Yuhong; Yang, Q. W.; Duan, Xuru

doi:10.1209/0295-5075/116/45003

Cited by 19 publications

(22 citation statements)

References 24 publications

(38 reference statements)

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“…This latter consideration enforces our instability identification, since Gene detected the excitation of this AITG mode at n = 6, where n is the toroidal wavenumber, which is reflected in the experimental measurements and numerical simulations documented in Ref. [31]. In the latter reference, AITG has been measured by multiple diagnostics lying in the frequency range 15 − 40 kHz, which is in good agreement with the frequency calculated by our numerical simulations.…”

Section: Linear Spectra Analysissupporting

confidence: 87%

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Impact of fast ions on a trapped-electron-mode dominated plasma in a JT-60U hybrid scenario

Mazzi¹,

Zarzoso²,

García³

et al. 2020

Nucl. Fusion

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The impact of fast ions on a trapped electron mode (TEM) is extensively analysed by linear and nonlinear gyrokinetic simulations for a JT-60U plasma at high β and low magnetic shear using the Gene code in local approximation. For the first time, it is shown that TEM-induced turbulent transport may remain unaffected by the steep fast ion pressure profile generated by the Neutral Beam Injection. Unlike recent observations of ion temperature gradient (ITG)-induced turbulent transport reductions due to fast ions, TEMdominated systems could act differently in the presence of a significant fast ion population. The possible role of zonal flows as a saturation mechanism is analyzed, showing that their weak impact in the reported JT-60U scenario might lead to different behaviour of fast ions with respect to the ITG-dominated discharges. It is also shown that Alfvénic shear modes are destabilized at low wave numbers (n 8). They are identified as drift Alfvén waves destabilized by ITG, which is a form of Alfvénic ITG instabilities. Deep numerical analysis provides the physical parameter range in which ITG-driven BAEs are stabilized. These results open the way to new possibilities of tailoring future experimental scenarios in order to benefit from transport reduction by fast ions.

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Section: Linear Spectra Analysissupporting

confidence: 87%

“…It must be noted however, that in Ref. [31], the rational surface q = 1 was present, whereas in the simulations presented here, q = 1.06.…”

Section: Linear Spectra Analysiscontrasting

confidence: 57%

Impact of fast ions on a trapped-electron-mode dominated plasma in a JT-60U hybrid scenario

Mazzi¹,

Zarzoso²,

García³

et al. 2020

Nucl. Fusion

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“…This dangerous instability has many properties of the theoretically predicted electromagnetic Alfvén ITG (AITG) [4][5][6], and is consistent with the linear gyrokinetic instability analysis [7]. In contrast with the previous claim of the AITG in an ohmic plasma with T i ≤ 0.75 keV without detectable magnetic fluctuationsb [8], the observed mode, considered as the AITG, is multiscale, has appreciableb, and is driven by thermal ions with T i > 10 keV.…”

supporting

confidence: 82%

Multiscale Chirping Modes Driven by Thermal Ions in a Plasma with Reactor-Relevant Ion Temperature

Hong

Heidbrink

et al. 2021

Phys. Rev. Lett.

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A thermal ion driven bursting instability with rapid frequency chirping, considered as an Alfvénic ion temperature gradient mode, has been observed in plasmas having reactor-relevant temperature in the DIII-D tokamak. The modes are excited over a wide spatial range from macroscopic device size to microturbulence size and the perturbation energy propagates across multiple spatial scales. The radial mode structure is able to expand from local to global in ∼0.1 ms and it causes magnetic topology changes in the plasma edge, which can lead to a minor disruption event. Since the mode is typically observed in the high ion temperature ≳10 keV and high-β plasma regime, the manifestation of the mode in future reactors should be studied with development of mitigation strategies, if needed. This is the first observation of destabilization of the Alfvén continuum caused by the compressibility of ions with reactor-relevant ion temperature.

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“…There are also recent reports of KBMs in experiments which exhibit low negative magnetic shear (Chen et al. 2016, 2018), where it is suggested that the same ion-magnetic-drift effect is responsible for the destabilization at small .…”

Section: Impact Of Average Magnetic Shear and Itgmentioning

confidence: 89%

Kinetic-ballooning-mode turbulence in low-average-magnetic-shear equilibria

et al. 2021

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Kinetic-ballooning-mode (KBM) turbulence is studied via gyrokinetic flux-tube simulations in three magnetic equilibria that exhibit small average magnetic shear: the Helically Symmetric eXperiment (HSX), the helical-axis Heliotron-J and a circular tokamak geometry. For HSX, the onset of KBM being the dominant instability at low wavenumber occurs at a critical value of normalized plasma pressure $\beta ^{\rm KBM}_{\rm crit}$ that is an order of magnitude smaller than the magnetohydrodynamic (MHD) ballooning limit $\beta ^{\rm MHD}_{\rm crit}$ when a strong ion temperature gradient (ITG) is present. However, $\beta ^{\rm KBM}_{\rm crit}$ increases and approaches the MHD ballooning limit as the ITG tends to zero. For these configurations, $\beta ^{\rm KBM}_{\rm crit}$ also increases as the magnitude of the average magnetic shear increases, regardless of the sign of the normalized magnetic shear. Simulations of Heliotron-J and a circular axisymmetric geometry display behaviour similar to HSX with respect to $\beta ^{\rm KBM}_{\rm crit}$ . Despite large KBM growth rates at long wavelengths in HSX, saturation of KBM turbulence with $\beta > \beta _{\rm crit}^{\rm KBM}$ is achievable in HSX and results in lower heat transport relative to the electrostatic limit by a factor of roughly five. Nonlinear simulations also show that KBM transport dominates the dynamics when KBMs are destabilized linearly, even if KBM growth rates are subdominant to ITG growth rates.

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Alfvénic ion temperature gradient activities in a weak magnetic shear plasma

Cited by 19 publications

References 24 publications

Impact of fast ions on a trapped-electron-mode dominated plasma in a JT-60U hybrid scenario

Impact of fast ions on a trapped-electron-mode dominated plasma in a JT-60U hybrid scenario

Multiscale Chirping Modes Driven by Thermal Ions in a Plasma with Reactor-Relevant Ion Temperature

Kinetic-ballooning-mode turbulence in low-average-magnetic-shear equilibria

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