Poloidal cross section of the W density reconstructed from SXR measurements in the JET plasma discharge 83351 at 10.42 s (left) and modelled with a combination of neoclassical drift-kinetic and turbulence gyro-kinetic codes (right). The low field side localization of the impurity produced by the centrifugal force affects both the neoclassical and the turbulent transport components and is identified as the cause of the observed start of central accumulation.
Graphs by Clemente Angioni.
The physics of impurity transport in tokamak plasmas, from A to Z recent progress and challenges
Seminar by Clemente Angioni, Max-Planck-Institut für Plasmaphysik, München, Germany
Abstract of talk
Impurities are an unavoidable and likely indispensable component of a fusion reactor plasma. The concentrations of the impurities and the shapes of their density profiles are determined by complex interactions among transport processes, particle sources and the impact of MHD instabilities. Impurity concentrations and density profile shapes have to be predicted, diagnosed and controlled, since they critically impact the discharge scenario and the plasma performance. Thereby, the study of impurity transport is an essential element towards the achievement of practical fusion energy. Impurities also provide an interesting piece of physics to investigate as the additional dependencies on the impurity mass A and the charge Z give rise to transport mechanisms which are practically absent or negligible for the main particle species.
Complete and reliable predictions of the impurity density profiles from the SOL to the magnetic axis still challenge present modelling capabilities. Nevertheless, the study of impurity transport has made important progress over the last decade, from the diagnostics, the experimental analysis techniques, as well as from the theoretical and modelling standpoints. In this talk, the current understanding of impurity transport, encompassing both heavy and light impurities, and comprising both neoclassical and turbulent transport, is presented. Emphasis is given to the physical aspects of the transport processes and on their importance to correctly model the experimental observations and to gain an understanding of the causes of impurity accumulation and accumulation avoidance. Evidences of disagreement between theory and measurements are also pointed out, and potential missing ingredients in the theoretical description are discussed.
N6115, Origo 6th floor, Fysikgården 2
30 January, 2017, 14:00
30 January, 2017, 15:00