| 1. |
- Anderson, Johan, 1973, et al.
(författare)
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Effects of cross-sectional elongation on the resistive edge modes
- 2001
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 8, s. 180-
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Tidskriftsartikel (refereegranskat)abstract
- Resistive edge modes in a shifted noncircular tokamak geometry are investigated in the electrostatic limit. The reduced Braghinskii equations are used as a model for the electrons and an advanced fluid model for the ions. An eigenvalue problem is derived from these equations which is solved numerically. It is found that the resistive ballooning modes are stabilized by plasma elongation forpeaked density profiles. In addition, it is found that the resistive ITG mode may be either stabilized or destabilized by elongation depending on the collision frequency.
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| 2. |
- Anderson, Johan, 1973, et al.
(författare)
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Electron geodesic acoustic modes in electron temperature gradient mode turbulence
- 2012
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 19:8
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the first demonstration of an electron branch of the geodesic acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for el-GAMsdriven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETGturbulence saturation level compared to the mixing length estimate.
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| 3. |
- Anderson, Johan, 1973, et al.
(författare)
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Secondary instability of electromagnetic ion-temperature-gradient modes for zonal flow generation
- 2011
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Ingår i: Physics of Plasmas. - 1089-7674 .- 1070-664X. ; 18:072306
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Tidskriftsartikel (refereegranskat)abstract
- An analytical model for zonal flow generation by toroidal ion-temperature-gradient (ITG) modes, including finite β electromagnetic effects, is derived. The derivation is based on a fluid model for ions and electrons and takes into account both linear and nonlinear β effects. The influence of finite plasma β on the zonal flow growth rate (γ_ZF) scaling is investigated for typical tokamak plasma parameters. The results show the importance of the zonal flows close to marginal stability where γ_ZF/γ_ITG ≫ 1 is obtained. In this region the parameter γ_ZF/γ_ITG increases with β, indicating that the ITG turbulence and associated transport would decrease with β at a faster rate than expected from a purely linear or quasi-linear analysis.
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| 4. |
- Anderson, Johan, 1973, et al.
(författare)
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Zonal flow generation in ITG turbulence
- 2002
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 9, s. 4500-
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Tidskriftsartikel (refereegranskat)abstract
- In the present work the zonal flow (ZF) growth rate in toroidal ion-temperature-gradient (ITG) mode turbulence including the effects of elongation is studied analytically. The scaling of the ZF growth with plasma parameters is examined for typical tokamak parameter values. The physical model used for the toroidal ITG driven mode is based on the ion continuity and ion temperature equations whereas the ZF evolution is described by the vorticity equation. The results indicate that a large ZFgrowth is found close to marginal stability and for peaked density profiles and these effects may be enhanced by elongation.
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| 5. |
- Fransson, Emil, 1986, et al.
(författare)
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Upgrade and benchmark of quasi-linear transport model EDWM
- 2022
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 29:11
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Tidskriftsartikel (refereegranskat)abstract
- The verification of a new saturation rule applied to the quasi-linear fluid model EDWM (extended drift wave model) and the calibration of several other features are presented. As one of the computationally fastest first-principle-based core transport models, EDWM can include an arbitrary number of ions and charge states. This feature is especially important for experimental devices with plasma-facing components made of heavy elements, such as the upcoming ITER device. As a quasi-linear model, EDWM solves a linear dispersion relation to obtain the instabilities driving the turbulence and combines the linear description with an estimation of the saturation level of the electrostatic potential to determine the fluxes. A new saturation rule at the characteristic length combined with a spectral filter for the poloidal wavenumber dependency is developed. The shape of the filter has been fitted against the poloidal wavenumber dependency of the electrostatic potential from non-linear gyrokinetic simulations. Additionally, EDWM's collision frequency and safety factor dependencies, as well as the electron heat flux level, have been calibrated against gyrokinetic and gyrofluid results. Finally, the saturation level has been normalized against non-linear gyrokinetic simulations and later validated against experimental measured fluxes from 12 discharges at JET.
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| 6. |
- Fülöp, Tünde, 1970, et al.
(författare)
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Turbulent and neoclassical impurity transport in tokamak plasmas
- 2009
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Ingår i: Physics of Plasmas. - 1089-7674 .- 1070-664X. ; 16:3, s. 032306-
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Tidskriftsartikel (refereegranskat)abstract
- Impurity particle transport in tokamaks is studied using an electrostatic fluid model for main ion andimpurity temperature gradient (ITG)͒ mode and trapped electron (TE͒) mode turbulence in thecollisionless limit and neoclassical theory. The impurity flux and impurity density peaking factorobtained from a self-consistent treatment of impurity transport are compared and contrasted with theresults of the often used trace impurity approximation. Comparisons between trace andself-consistent turbulent impurity transport are performed for ITER-like profiles. It is shown that forsmall impurity concentrations the trace impurity limit is adequate if the plasma is dominated by ITGturbulence. However, in case of TE mode dominated plasmas the contribution from impurity modesmay be significant, and therefore a self-consistent treatment may be needed.
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| 7. |
- Singh, R, et al.
(författare)
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A semi-analytic power balance model for low (L) to high (H) mode transition power threshold
- 2014
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 21:6, s. 062503-
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Tidskriftsartikel (refereegranskat)abstract
- We present a semi-analytic model for low (L) to high (H) mode transition power threshold (P-th). Two main assumptions are made in our study. First, high poloidal mode number drift resistive ballooning modes (high-m DRBM) are assumed to be the dominant turbulence driver in a narrow edge region near to last closed flux surface. Second, the pre-transition edge profile and turbulent diffusivity at the narrow edge region pertain to turbulent equipartition. An edge power balance relation is derived by calculating the dissipated power flux through both turbulent conduction and convection, and radiation in the edge region. P-th is obtained by imposing the turbulence quench rule due to sheared E x B rotation. Evaluation of P-th shows a good agreement with experimental results in existing machines. Increase of P-th at low density (i.e., the existence of roll-over density in P-th vs. density) is shown to originate from the longer scale length of the density profile than that of the temperature profile.
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| 8. |
- Singh, Rameswar, et al.
(författare)
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Symmetry breaking effects of density gradient on parallel momentum transport: A new ρ* effect
- 2012
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- Symmetry breaking effects of density gradient on parallel momentum transport is studied via quasilinear theory. It is shown that finite (equivalent to rho(s)/L-n), where rho(s) is ion sound radius and L-n is density scale length, leads to symmetry breaking of the ion temperature gradient (ITG) eigenfunction. This broken symmetry persists even in the absence of mean poloidal (from radial electric field shear) and toroidal flows. This effect, as explained in the text, originates from the divergence of polarization particle current in the ion continuity equation. The form of the eigenfunction allows the microturbulence to generate parallel residual stress via symmetry breaking. Comparison with the (E) over right arrow x (B) over right arrow shear driven parallel residual stress, parallel polarization stress and turbulence intensity gradient driven parallel residual stress are discussed. It is shown that this rho(s)* driven parallel residual stress may become comparable to (E) over right arrow x (B) over right arrow shear driven parallel residual stress in small L-n region. In the regular drift wave ordering, where rho(s)*
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| 9. |
- Skyman, Andreas, 1982, et al.
(författare)
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Gyrokinetic modelling of stationary electron and impurity profiles in tokamaks
- 2014
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 21:9, s. 092305-
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Tidskriftsartikel (refereegranskat)abstract
- Particle transport due to Ion Temperature Gradient (ITG)/Trapped Electron Mode (TEM) turbulence is investigated using the gyrokinetic code GENE. Both a reduced quasilinear treatment and nonlinear simulations are performed for typical tokamak parameters corresponding to ITG dominated turbulence. The gyrokinetic results are compared and contrasted with results from a computationally efficient fluid model. A selfconsistent treatment is used, where the stationary local profiles are calculated corresponding to zero particle flux simultaneously for electrons and trace impurities. The scaling of the stationary profiles with magnetic shear, safety factor, electron-to-ion temperature ratio, collisionality, toroidal sheared rotation, plasma β, triangularity, and elongation is investigated. In addition, the effect of different main ion mass on the zero flux condition is discussed. The electron density gradient can significantly affect the stationary impurity profile scaling. It is therefore expected that a selfconsistent treatment will yield results more comparable to experimental results for parameter scans where the stationary background density profile is sensitive. This is shown to be the case in scans over magnetic shear, collisionality, elongation, and temperature ratio, for which the simultaneous zero flux electron and impurity profiles are calculated. A slight asymmetry between hydrogen, deuterium, and tritium with respect to profile peaking is obtained, in particular, for scans in collisionality and temperature ratio.
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| 10. |
- Skyman, Andreas, 1982, et al.
(författare)
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Impurity transport in temperature gradient driven turbulence
- 2012
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 19:3, s. 032313-
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper, the transport of impurities driven by trapped electron (TE) mode turbulence is studied. Non-linear (NL) gyrokinetic simulations using the code GENE are compared with results from quasilinear (QL) gyrokinetic simulations and a computationally efficient fluid model. The main focus is on model comparisons for electron temperature gradient driven turbulence regarding the sign of the convective impurity velocity (pinch) and the impurity density gradient R/LnZ (peaking factor) for zero impurity flux. In particular, the scaling of the impurity peaking factors with impurity charge Z and with driving temperature gradient is investigated and compared with results for the more studied ion temperature gradient (ITG) driven turbulence. The question of helium ash removal in TE mode turbulence is also investigated. In addition, the impurity peaking is compared to the main ion peaking obtained by a self-consistent fluid calculation of the density gradients corresponding to zero particle fluxes. For the scaling of the peaking factor with impurity charge Z, a weak dependence is obtained from NL GENE and fluid simulations. The QL GENE results show a stronger dependence for low Z impurities and overestimates the peaking factor by up to a factor of two in this region. As in the case of ITG dominated turbulence, the peaking factors saturate as Z increases, at a level much below neoclassical predictions. The scaling with Z is, however, weak or reversed as compared to the ITG case. The results indicate that TE mode turbulence is as efficient as ITG turbulence at removing He ash, with DHe/χeff>1.0. The scaling of impurity peaking with the background temperature gradients is found to be weak in the NL GENE and fluid simulations. The QL results are also here found to significantly overestimate the peaking factor for low Z values. For the parameters considered, the background density gradient for zero particle flux is found to be slightly larger than the corresponding impurity zero flux gradient.
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