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- Nordman, Hans, 1957, et al.
(författare)
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Fluid and gyrokinetic simulations of impurity transport at JET
- 2011
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 53:10, s. 105005-
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Tidskriftsartikel (refereegranskat)abstract
- Impurity transport coefficients due to Ion-Temperature-Gradient (ITG) mode and Trapped-Electron (TE) mode turbulence are calculated using profile data from dedicated impurity injection experiments at JET. Results obtained with a multi-fluid model are compared with quasi-linear and nonlinear gyrokinetic simulation results obtained with the code GENE. The sign of the impurity convective velocity (pinch) and its various contributions are discussed. The dependence of the impurity transport coefficients and impurity peaking factor -∇nZ/nZ on plasma parameters like impurity charge number Z, ion logarithmic temperature gradient, collisionality, ExB shearing, and charge fraction are investigated. It is found that for the studied ITG dominated JET discharges, both the fluid and gyrokinetic results show an increase of the impurity peaking factor for low Z-values followed by a saturation at moderate values of impurity peaking, much below the neoclassical predictions, for large values of Z. The results are in qualitative agreement with the experimental trends observed for the injected impurities (Ne, Ar, Ni) whereas for the background carbon species the observed flat or weakly hollow C profiles are not well reproduced by the simulations.
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| 2. |
- Skyman, Andreas, 1982, et al.
(författare)
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Turbulent impurity transport driven by temperature and density gradients
- 2011
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Ingår i: 13th International Workshop on H-mode Physics and Transport Barriers.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The modelling of a modern fusion device is very challenging both theoretically and numerically, much owing to turbulence driven by sharp gradients in density and temperature. However, understanding the resulting transport is crucial for the success of future fusion devices such as ITER.In this work, the turbulent transport of trace impurities in a tokamak device has been studied through quasilinear (QL) and non-linear (NL) gyrokinetic simulations using the GENE code.The parameters are chosen for trapped electron (TE) mode turbulence, driven primarily by steep electron density gradients relevant to H-mode physics, but with a transition to temperature gradient driven turbulence as the density gradient flattens.The results are quantitative assessments of the transport properties of several impurity species, and the dependence thereof on various plasma parameters.
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| 3. |
- Skyman, Andreas, 1982
(författare)
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Turbulent impurity transport in tokamak fusion plasmas
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the enormous growth of high performance computing (HPC) over the last few decades, plasma physicists have gained access to a valuable instrument for investigating turbulent plasma behaviour. In this thesis, these tools are utilised for the study of particle transport in fusion devices of the tokamak variety, focusing in particular on the transport of impurities.The transport properties of impurities is of high relevance for the performance and optimisation of magnetic fusion devices. For instance, the possible accumulation of He ash in the core of the reactor plasma will serve to dilute the fuel, thus lowering fusion power. Heavier impurity species, originating from the plasma-facing surfaces, may also accumulate in the core, and wall-impurities of relatively low density may lead to unacceptable energy losses in the form of radiation. In an operational power plant, such as the ITER device, both impurities of low and high charge numbers will be present.This thesis studies turbulent impurity transport driven by two different modes of drift wave turbulence: the trapped electron (TE) and ion temperature gradient (ITG) modes. Principal focus is on the balance of convective and diffusive impurity transport, as quantified by the impurity density gradient of zero flux (“peaking factor”, PF ). The results are scalings of PF with impurity charge number, as well as with the driving background gradients of temperature and density, as well as other plasma parameters.Quasi- and nonlinear results are obtained using the gyrokinetic code GENE, and compared with results from a computationally efficient multi-fluid model. In general, the three models show a good qualitative agreement. Results for ITG mode driven impurity transport are also compared with experimental results from the Joint European Torus, and also in this case a good qualitative agreement is obtained.
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