A quasi-linear analysis of the impurity effect on turbulent momentum transport and residual stress

Ko, S. H.; Jhang, Hogun; Singh, Rameswar

doi:10.1063/1.4927779

Cited by 6 publications

(2 citation statements)

References 51 publications

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“…This suggests that the ITG modes are damped by impurity ions. The stabilizing effect of impurities is consistent with previous research results, because when the gradient of the impurity ions is the same as the electron density gradient, the dominant ion density is diluted (the relationship between the ion density gradient and the fraction of impurities is presented by equation ( 8)) [28][29][30][31][32], which makes the impurity ion effect weaken the driving force of the ITG and stabilizes the ITG mode. Most importantly, the impurity increases the growth rate of the ITG mode, which is very different in the weak density gradient case.…”

Section: Dependence On the Itgsupporting

confidence: 90%

Effects of trapped electrons on the ion temperature gradient mode in tokamak plasmas with hollow density profiles

Dong

Liu

2020

Plasma Sci. Technol.

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The ion temperature gradient (ITG) mode in the presence of impurity ions and trapped electrons (TEs) is numerically investigated in tokamak plasmas with hollow density profiles, using the gyrokinetic integral eigenmode equation. It is found that in the inverted density plasma, the increase of the ITG enhances the growth rate and frequency of the ITG, and the density gradient plays an important role in the ITG modes. For weak density gradient situations, the trapped electron effects increase the instability of the ITG, while the impurity has an obviously stabilizing effect. For the strong density gradient cases, both the impurities and trapped electrons enhance the ITG instabilities. In addition, it is shown that the growth rate of the ITG decreases with positive magnetic shear s while the real frequency increases with positive magnetic shear. The growth rate of the ITG increases with negative magnetic shear s while the real frequency decreases with negative magnetic shear. The length of the calculated mode structure in the positive and negative magnetic shear intervals is also presented.

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Section: Dependence On the Itgsupporting

confidence: 90%

Effects of trapped electrons on the ion temperature gradient mode in tokamak plasmas with hollow density profiles

Dong

Liu

2020

Plasma Sci. Technol.

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“…Besides, gyrokinetic analysis with CGYRO code shows that a transport bifurcation from the kinetic ballooning mode to TEM limits the transport and results in the formation of a high-pressure staircase pedestal which is beneficial for the DIII-D tokamak confinement [21]. Therefore, various physical effects including finite Larmor radius (FLR) [22], magnetic shear [23], independent temperature and density gradients [24,25], and impurity ions [26,27] were taken into account in fluid [28,29], kinetic [30,31], or combined models [32], which can be used to focus on the coupling modes.…”

Section: Introductionmentioning

confidence: 99%

Tungsten impurity effects on the coupling of TEM and ITG mode in reversed magnetic shear tokamak plasmas

Liu¹,

Dong²,

Du³

et al. 2021

Plasma Phys. Control. Fusion

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The trapped electron mode (TEM) and ion temperature gradient (ITG) mode may couple into one hybrid mode or coexist simultaneously, depending on the regime of tokamak plasma parameters. A gyrokinetic integral eigenvalue equation is applied to investigate the coupling of TEM and ITG mode in the presence of tungsten (W) impurity in tokamak geometry of reversed magnetic shear (RMS). Systematic analysis of W impurity effects on the mode characteristics and induced quasi-linear particle flux has been performed in a wide regime of plasma parameters such as density gradient L e z = L n e / L n z , charge concentration f z , and charge number Z of impurity ions, and poloidal wave number k θ ρ s spectrum. It is found that both RMS and the impurity ions with inwardly peaked density profile and high charge concentration have strongly stabilizing effects on the modes. Furthermore, the increasing Z tends to decouple the hybrid mode into coexisting modes or dominating TEM/ITG mode in different parameter regions. The significance of the results for the particle transport of impurity and main ions as well as electrons in advanced tokamaks with W components is discussed.

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Enhancement of residual stress by electromagnetic fluctuations: A quasi-linear study

et al. 2016

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A study is conducted on the impact of electromagnetic (EM) fluctuations on residual Reynolds stress in the context of the quasi-linear theory. We employ a fluid formulation describing EM ion temperature gradient turbulence. Analyses show that finite plasma β (=plasma thermal energy/magnetic energy) significantly increases the residual stress, potentially leading to the strong enhancement of flow generation in high β plasmas. We identify that this strong increase of residual stress originates from the reinforcement of radial ⟨k∥⟩ (=spectrally averaged parallel wavenumber) asymmetry due to the deformation of eigenfunctions near a rational surface.

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A quasi-linear analysis of the impurity effect on turbulent momentum transport and residual stress

Cited by 6 publications

References 51 publications

Effects of trapped electrons on the ion temperature gradient mode in tokamak plasmas with hollow density profiles

Effects of trapped electrons on the ion temperature gradient mode in tokamak plasmas with hollow density profiles

Tungsten impurity effects on the coupling of TEM and ITG mode in reversed magnetic shear tokamak plasmas

Enhancement of residual stress by electromagnetic fluctuations: A quasi-linear study

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