Properties of ubiquitous modes in tokamak plasmas

Shen, Yong; Dong, J. Q.; Li, J.; Han, Mingkun; Li, J. Q.; Sun, A.P.; Qu, Hongpeng

doi:10.1088/1741-4326/ab2e95

Cited by 5 publications

(20 citation statements)

References 36 publications

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“…The result implies that it is easy for the TEM changing into the regime of ubiquitous mode with the increasement of the fraction of trapped electrons. Similar result is displayed in the research [39] with gyrokinetic simulations. With further searching, the nonlinear transports are displayed.…”

Section: Parameter Dependencesupporting

confidence: 90%

“…For this reason, the ubiquitous mode is a significant branch of TEMs and should receive more considerations in turbulent transport analysis. [38,39] Thereby, the characters of the ubiquitous mode and the influence on the transport have to be revealed. This research will help us to better reveal the physical characters of ubiquitous mode and the role of the ubiquitous mode in tokamak transport.…”

Section: Introductionmentioning

confidence: 99%

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Features of transport induced by ion-driven trapped-electron modes in tokamak plasmas

Wang

et al. 2023

Chinese Phys. B

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As an obstacle in high-performance discharge in future fusion devices, disruptions may do great damages to the reactors through causing strong electromagnetic forces, heat loads and so on. The drift waves in tokamak are illustrated to play essential roles in the confinement performance as well. Depending on the plasma parameters and mode perpendicular wavelength, the mode phase velocity is either in the direction of electron diamagnetic velocity (namely, typical trapped electron mode) or in the direction of ion diamagnetic velocity (namely, the ubiquitous mode). Among them, the ubiquitous mode was directly investigated using gyro-fluid simulation associating with gyro-fluid equations for drift waves in tokamak plasmas. The ubiquitous mode is charactered with the short wavelength and propagates in ion diamagnetic direction. It is suggested that the density gradient is essential for the occurrence of the ubiquitous mode. However, the ubiquitous mode is also influenced with the temperature gradients and other plasma parameters including the magnetic shear and the fraction of trapped electrons. Furthermore, the ubiquitous mode may play essential roles in the turbulent transport. Meanwhile, the relevant parameters are scanned using a great number of electrostatic gyro-fluid simulations. The stability map is taken into consideration with the micro-instabilities contributing to the turbulent transport. The ‘stability valley’ of the growth rates occurs with the assumption of the normalized temperature gradient equaling to the normalized density gradient.

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Section: Parameter Dependencesupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Features of transport induced by ion-driven trapped-electron modes in tokamak plasmas

Wang

et al. 2023

Chinese Phys. B

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“…first increase gradually until sˆ= 0.5, and then decrease with s. ˆFor the latter case (  s 0.5 ˆ), as sˆincreases, the mode growth rate would decrease and the UM instability window becomes narrower, as demonstrated in figure 9(a). It can be understood that the occurrence of the UM impose a limitation on the value of s, ˆand the smaller value of sˆis more preferable for exciting the UM [13]. Physically, this is due to the suppressing effect of the magnetic shear on the UM.…”

Section: The Fraction Of Trapped Electrons Parametric Dependencementioning

confidence: 99%

“…The significance of UMs in magnetically confined plasma has been well recognized since UMs can lead to relatively strong anomalous diffusion. Recently, we extended [13] the study of Coppi et al [10][11][12] and clarified many novel properties of UMs, employing the gyrokinetic model for low frequency drift instability on tokamaks.…”

Section: Introductionmentioning

confidence: 96%

“…In order to explore the influence of impurity on drift wave turbulence, in recent years, the impurity effects on ITG and TEM instability have been investigated [26][27][28][29][30][31][32]. As an important branch of TEMs, UMs deserve more attentions in transport analysis due to the fact that although UMs cause less transport than ty-TEM, ITG, and ETG modes in general, under some specific parameters, UMs can cause strong heat diffusions, especially in the regime of fluid-like instability (FLI) [12,13]. Thereby, the effects of impurity ions on UMs have to be investigated.…”

Section: Introductionmentioning

confidence: 99%

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Numerical study of ubiquitous modes in tokamak plasmas in the presence of impurities

Shen

Dong

Peng

et al. 2020

Plasma Phys. Control. Fusion

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As an important branch of trapped electron modes (TEMs), the ubiquitous mode (UM) is a favored subject for the investigation of anomalous energy losses in magnetic fusion plasmas. In this paper, the numerical study of UMs was carried out in tokamak plasmas in the presence of impurities. The physical model and the gyrokinetic equations for TEM (and UM) instability is introduced, including the impurity effect. The numerical results show that impurity species impose significant impacts on the UM instability in many ways, one of which is that impurity effect on UMs is generally stabilizing, and on the whole the stabilizing effect is most pronounced for the case of −0.8 ≲ L ez < 0 ( L ez ≡ L n e / L n z , with L n s = − ∂ ln n s / ∂ r − 1 ). As the impurity charge concentration f z increases, or for the heavier or lower-ionized impurity ions, the UM instability is weaker. Compared to the ion and electron temperature gradient effects, impurity temperature gradient (expressed by η z = L nz / L Tz ) has only a minor effect, while the ratio of electron to impurity temperature τ z has a relatively larger effect on UMs, embodied in the mode linear growth rates and instability windows. The investigation of wavenumber threshold for UM showed that the mode was a fluid-like instability when b i ≡ 1 2 k θ 2 ρ s 2 ∼ n / n e T 3 , and the presence of impurity resulted in the modification of the UM instability window. By surveying the parametric dependences of UMs in the presence of impurities, it is revealed that comparatively, the stabilizing effects of impurity is more pronounced in the regime of larger wavenumber, while the weakening effects of (i) decreasing the fraction of trapped electrons, (ii) increasing the magnetic shear, or (iii) decreasing the electron density gradient on UM instability are relatively more pronounced in the regime of smaller wavenumber. It also indicates that the stabilizing effect of impurity on UMs is owing to the non-resonant mechanism of the UM.

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Transport from electron-scale turbulence in toroidal magnetic confinement devices

Ren,

Guttenfelder,

Kaye

et al. 2024

Rev. Mod. Plasma Phys.

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Properties of ubiquitous modes in tokamak plasmas

Cited by 5 publications

References 36 publications

Features of transport induced by ion-driven trapped-electron modes in tokamak plasmas

Features of transport induced by ion-driven trapped-electron modes in tokamak plasmas

Numerical study of ubiquitous modes in tokamak plasmas in the presence of impurities

Transport from electron-scale turbulence in toroidal magnetic confinement devices

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