Effects of the equilibrium model on impurity transport in tokamaks

Skyman, Andreas; Fazendeiro, Luis; Tegnered, Daniel; Nordman, Hans; Anderson, Johan; Strand, Pär

doi:10.1088/0029-5515/54/1/013009

Cited by 14 publications

(23 citation statements)

References 50 publications

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“…35 Very recently, the effects of the equilibrium model on impurity transport in ITG/TE-mode-driven turbulence have been studied using gyrokinetic code GENE, and the numerical results have been compared with the observations in JET. 36 Here, we come to discuss the effects of elongation and its radial derivative on the linear impurity mode in the simplest case of g i ¼ 0:0 (to avoid the ITG mode). ðj À 1:0Þ=j and s j ¼ ðj À 1:0Þ=2j are defined as the elongation derivative.…”

Section: E L Ez Threshold For Exciting the Impurity Modesmentioning

confidence: 99%

Impurity effects on short wavelength ion temperature gradient mode in elongated tokamak plasmas

Wang

Dong

2015

Physics of Plasmas

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The effects of impurity ions on the short wavelength ion temperature gradient (SWITG) driven instability in elongated tokamak plasmas are numerically investigated with the gyrokinetic integral eigenmode equation. It is found that for a moderate electron density gradient, the SWITG mode is first destabilized and then stabilized with increasing elongation j, which is different from the conventional long wavelength ITG mode. For a large electron density gradient, the elongation can effectively stabilize the SWITG mode. Moreover, the low Z impurity ions with inwardly (outwardly) peaked density profiles have stabilizing (destabilizing) effects on the SWITG modes in elongated plasmas. Interestingly, the high Z tungsten impurity ions with inwardly peaked density profiles play a stronger stabilizing role in the SWITG modes than the low Z impurity ions (such as carbon and oxygen) do. In particular, the high Z tungsten impurity ions with a weakly outwardly peaked density profile still have a stabilizing effect. Finally, the critical threshold of impurity density gradient scale length for exciting impurity mode is also numerically obtained, indicating that the impurity mode is harder to be excited in elongated plasmas than in circular ones. V C 2015 AIP Publishing LLC. [http://dx.

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Section: E L Ez Threshold For Exciting the Impurity Modesmentioning

confidence: 99%

Impurity effects on short wavelength ion temperature gradient mode in elongated tokamak plasmas

Wang

Dong

2015

Physics of Plasmas

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“…3 where a negative particle flux represents an inward motion of impurities. In recent studies (see for example [43,44]), the dimensionless zero flux peaking factor, a/L n He2+ = −av He /D He , calculated from gyrokinetic simulations in the limit of Γ He2+ = 0, is of value in describing steady state density profiles that can be achieved in the absence of a central source.…”

Section: Role Of Anomalous Transportmentioning

confidence: 99%

Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST

et al. 2014

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Time-dependent helium gas puff experiments have been performed on the Mega Ampère Spherical Tokamak (MAST) during a two point plasma current scan in L-mode and a confinement scan at 900 kA. An evaluation of the He II (n = 4 → 3) spectrum line induced by charge exchange suggests anomalous rates of diffusion and inward convection in the outer regions of both L-mode plasmas. Similar rates of diffusion are found in the H-mode plasma, however these rates are consistent with neoclassical predictions. The anomalous inward pinch found in the core of L-mode plasmas is also not apparent in the H-mode core. Linear gyrokinetic simulations of one flux surface in L-mode using the gs2 and gkw codes find that equilibrium flow shear is sufficient to stabilise ITG modes, consistent with BES observations, and suggest that collisionless TEMs may dominate the anomalous helium particle transport. A quasilinear estimate of the dimensionless peaking factor associated with TEMs is in good agreement with experiment. Collisionless TEMs are more stable in H-mode because the electron density gradient is flatter. The steepness of this gradient is therefore pivotal in determining the inward neoclassical particle pinch and the particle flux associated with TEM turbulence.

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“…To perform these simulations, the same number of polynomials are used in NEO (5), and a limited number are then read in GKW to reconstruct the distribution function. Going from one to two Laguerre polynomials leads to a quantitative change in the turbulent roto-diffusion at all collisionalities.…”

Section: Discussionmentioning

confidence: 99%

Impact of the neoclassical distribution function on turbulent impurity and momentum fluxes: fluid model and gyrokinetic simulations

Manas¹,

Hornsby²,

Angioni³

et al. 2017

Plasma Phys. Control. Fusion

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The impact of the neoclassical background on turbulent impurity transport is investigated by means of gyrokinetic simulations supported by fluid equations. The latter are derived, using a Laguerre polynomials expansion of the first order neoclassical distribution function, and analytical expressions of the turbulent momentum flux and impurity transport coefficients are assessed. Comparisons of gyrokinetic simulations including this neoclassical background (coupling between the codes GKW and NEO) and the fluid model are used to identify the main mechanisms behind the modification of the turbulent transport channels and benchmark the numerical implementation. These mechanisms include a modification of the parallel dynamics of the main ions and direct contributions stemming from the asymmetry in the parallel velocity space of the neoclassical distribution function. The latter which is found dominant for turbulent impurity transport, increases with increasing collisionality, R/LT i , R/Ln, impurity mass, safety factor and aspect ratio. These contributions to momentum and impurity fluxes are also found to depend on the directions of the toroidal magnetic field and plasma current.

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Effects of the equilibrium model on impurity transport in tokamaks

Cited by 14 publications

References 50 publications

Impurity effects on short wavelength ion temperature gradient mode in elongated tokamak plasmas

Impurity effects on short wavelength ion temperature gradient mode in elongated tokamak plasmas

Neoclassical and gyrokinetic analysis of time-dependent helium transport experiments on MAST

Impact of the neoclassical distribution function on turbulent impurity and momentum fluxes: fluid model and gyrokinetic simulations

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