Predictive modelling of impurity seeded plasmas in JET

Seeding of impurities into JET resulted in a pronounced modification of plasma confinement properties. In order to analyse the underlying mechanisms a predictive transport modelling has been performed by means of two approaches. (i) The Chalmers advanced fluid model for temperature gradient driven instabilities is applied to determine all transport coefficients necessary for transport modelling. In the present code computations the radial profiles of the particle densities and temperatures are computed using experimentally measured sources. The computations give good agreement of the temperature profiles with the measured ones. (ii) The Jülich transport model, used earlier to simulate the plasma evolution in TEXTOR radiative improved mode, has been amended by a proper description of trapped electron transport, which is important at low collisionality typical for JET. This model incorporated into the transport code RITM, which self-consistently computes particle sources due to plasma recycling and impurity ionization, reproduces well the peaking in density and pressure profiles caused by impurity seeding.