| 1. |
- Anderson, Johan, 1973, et al.
(author)
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High frequency geodesic acoustic modes in electron scale turbulence
- 2013
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:12, s. article nr. 123016-
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Journal article (peer-reviewed)abstract
- In this work the finite β-effects 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-GAMs driven non-linearly by ETG modes is derived. The ETG growth rate from the fluid model is compared with the results found from gyrokinetic simulations with good agreement. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared with the mixing length estimate. It is shown that the el-GAM may be stabilized by an increase in finite β as well as by increasing non-adiabaticity. The decreased GAM growth rates is due to the inclusion of the Maxwell stress.
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| 2. |
- Anderson, Johan, 1973, et al.
(author)
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High Frequency Geodesic Acoustic Modes in Electron Scale Turbulence
- 2012
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In: Proceedings 24th IAEA FEC, San Diego 8-13 October 2012.
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Conference paper (peer-reviewed)abstract
- In this work the first demonstration of a high frequency branch of the geodesic acoustic mode (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 high frequency GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with high frequency GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate.
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| 3. |
- Fazendeiro, Luis, 1976, et al.
(author)
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Gyrokinetic simulations of turbulent transport in JET-like plasmas
- 2013
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In: 40th European Physical Society Conference on Plasma Physics. ; 2, s. 1074-1077
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Conference paper (other academic/artistic)abstract
- In this work turbulent transport in JET-like plasma discharges is analyzed, with main emphasison impurity transport driven by ITG/TEM modes. Gyrokinetic (GK) simulations are performedusing the GENE code [1, 2], in both quasilinear (QL) and nonlinear (NL) mode,1 and the resultsare compared with a computationally efficient fluid model [3, 4]. Particle transport is quantifiedby locally finding density gradients (R/Ln ) that yield zero particle flux, signifying a balancebetween convective and diffusive transport.The impact of the magnetic equilibrium (circular, s − α and realistic magnetic geometry) onthe various models is discussed, as well as the effects of collisionality (in both fluid and GK)and the inclusion of a (2%) Carbon background (in GK), as per JET CFC wall conditions. Theeffect of sheared toroidal rotation was also investigated and found to be important, although notfor the particular JET discharge studied in this work.
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| 4. |
- Skyman, Andreas, 1982, et al.
(author)
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Effects of the equilibrium model on impurity transport in tokamaks
- 2014
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 54:1, s. 013009-
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Journal article (peer-reviewed)abstract
- Gyrokinetic simulations of ion temperature gradient mode and trapped electron mode driven impurity transport in a realistic tokamak geometry are presented and compared with results using simplified geometries. The gyrokinetic results, obtained with the GENE code in both linear and non-linear modes are compared with data and analysis for a dedicated impurity injection discharge at JET. The impact of several factors on heat and particle transport is discussed, lending special focus to tokamak geometry and rotational shear. To this end, results using s–α and concentric circular equilibria are compared with results with magnetic geometry from a JET experiment. To further approach experimental conditions, non-linear gyrokinetic simulations are performed with collisions and a carbon background included.The impurity peaking factors, computed by finding local density gradients corresponding to zero particle flux, are discussed. The impurity peaking factors are seen to be reduced by a factor of ~2 in realistic geometry compared with the simplified geometries, due to a reduction of the convective pinch. It is also seen that collisions reduce the peaking factor for low-Z impurities, while increasing it for high charge numbers, which is attributed to a shift in the transport spectra towards higher wavenumbers with the addition of collisions. With the addition of roto-diffusion, an overall reduction of the peaking factors is observed, but this decrease is not sufficient to explain the flat carbon profiles seen at JET.
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| 5. |
- Skyman, Andreas, 1982, et al.
(author)
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Particle transport in ion and electron scale turbulence
- 2012
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In: Proceedings of 24th Fusion Energy Conference -- IAEA CN-197.
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Conference paper (other academic/artistic)abstract
- This work deals with transport of main ions and impurities in micro turbulence driven by ion and electron temperature gradients, and trapped electrons. Results are obtained for both non- and quasi-linear simulations, using the gyrokinetic code GENE. Transport properties are quantified by the gradient of zero particle flux for steady state in source free regions.Results are compared with results obtained using a computationally efficient fluid model. Of particular interest are conditions of steep gradients, relevant to eg. transport barriers. Results from s–α geometry are compared with results with a JET-like magnetic equilibrium, and the effects on transport investigated. Further, the quality of He ash removal is studied.
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| 6. |
- Skyman, Andreas, 1982, et al.
(author)
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Particle transport in ion and electron scale turbulence
- 2012
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In: Proceedings of 24th Fusion Energy Conference -- IAEA CN-197.
-
Conference paper (peer-reviewed)abstract
- Micro turbulent modes have important and non-trivial effects on transport in tokamaks. This paper deals with transport of main ions and impurities in ion and electron scale turbulence, driven by ion and electron temperature gradients, and trapped electrons. Using the gyrokinetic Vlasov code GENE, results are obtained from both nonlinear and quasi-linear simulations. The transport properties are quantified by calculating the gradient of zero particle flux for steady state in source free regions of the plasma. The results are compared and contrasted with results obtained using a computationally efficient fluid model.Of particular interest are conditions of steep gradients, relevant to e.g. transport barrier conditions. Further, results from a simple s–α geometry are compared with results obtained using a JET-like magnetic equilibrium, and the effects on transport investigated.
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| 7. |
- Skyman, Andreas, 1982, et al.
(author)
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Turbulent particle transport driven by ion and electron modes
- 2012
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In: EPS 2012.
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Conference paper (other academic/artistic)abstract
- The topic of this work is turbulent transport of main ionsand impurities driven by ion (ITG) and electron modes (TE and electron scale ETG) in tokamaks. Regions relevant to the pedestal of H-mode plasmas (i.e. steep density gradients) are of particular interest. Using the code GENE, quasilinear (QL) and nonlinear (NL) gyrokinetic simulations are performed. Results are compared with a computation ally efficient fluid model.Transport is quantified by the density gradient of zero particle flux, related to the balance of convection and diffusion. This measure of the impurity peaking is calculated for ITG and TE mode turbulence, and conditions for zero main ion flux is investigated for ETG. Further, the quality of He ash removal is studied.
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| 8. |
- Skyman, Andreas, 1982, et al.
(author)
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Turbulent particle transport driven by ion and electron modes
- 2012
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In: Proceedings of EPS 2012, Europhysics Conference Abstracts. - 2914771797 ; 36F, s. P5.033-
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Conference paper (peer-reviewed)abstract
- The topic of the present work is the turbulent transport of main ions and impurities driven by ion modes (ITG) and electron modes (TE and electron scale ETG). Particle transport in regions relevant to the pedestal region of H-mode plasmas, i.e. with steep density gradients, are of particular interest. Using the code GENE, quasi- and nonlinear gyrokinetic simulations are performed, and the results are compared with a computationally efficient fluid model.The transport properties are quantified by locally finding density gradients (R/Ln ) yielding zero particle flux, which are directly related to the balance of convective and diffusive transport.This measure of the impurity peaking is calculated for ITG and TE mode turbulence in source-free regions of the plasma, and scalings are obtained for the driving gradients and the impurity charge number (Z). Further, the quality of the helium ash removal is studied for ITG and TE mode drive turbulence. For ETG modes, the focus is on the main ion transport, and the density gradient leading to zero main ion particle flux, related to the formation and sustainment of the edge pedestal, is estimated.
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