Over the last two years, several experiments relevant for the study of particle transport and density profile evolution, have been performed at JET. They can be classified as stationary discharges with and without central particle source due to the beams, quasi-stationary discharges with deuterium gas puffing, deep pellet fuelled discharges and discharges perturbed by cold pulses obtained by shallow pellet injection. All these experimental scenarios have been simulated by means of the JETTO transport code, employing different transport models: purely empirical models and the semi-empirical mixed Bohm/gyro-Bohm transport model, both with the addition of different theory-based expressions for the anomalous particle pinch and the first principle Weiland transport model. The coefficients used to scale the pinch velocity in the purely empirical and in the mixed Bohm/gyro-Bohm model have been varied from shot to shot. In this paper, the results of the simulations are presented. The main conclusions are that, for the cases studied in this paper, the sawtooth activity is the main particle transport mechanism in the plasma centre (r/a ⩽ 0.5). Nevertheless, to reproduce the density profile in the gradient zone (0.5 ⩽ r/a ⩽ 0.9), an anomalous pinch seems to be necessary, at least for L-mode plasmas. This anomalous convective flux is well reproduced by the off-diagonal elements of the transport matrix given by the Weiland model.

For the first time, the predictive capabilities of the mixed Bohm/GyroBohm, Weiland and ‘retuned’ GLF23 transport models are investigated with ITB discharges from the ITPA ITB database with fully predictive, time-dependent transport simulations. A range of plasma conditions is examined for JET, JT-60U and DIII-D discharges with internal transport barriers (ITBs). The simulations show that the Bohm/GyroBohm model is able to follow the time evolution of the discharge from the preheating phase without an ITB through the ITB onset phase until the high performance phase with fair accuracy in most cases in JET and JT-60U. This indicates the importance of the interplay between the magnetic shear and ωE×B flow shear in ITB formation since these are the mechanisms that govern the ITB physics in the model. In order to achieve good agreement in DIII-D, the α-stabilization had to be included in the model, emphasizing the role played by the α-stabilization in the physics of the ITBs. The Weiland and GLF23 transport models show limited agreement between the model predictions and experimental time evolution of the ITB and kinetic plasma profiles. The Weiland model does not form a clear ITB in any of the three tokamaks despite varying plasma profiles, such as the q-profile. On the other hand, the average temperatures and density are often in fair agreement with experimental values. The GLF23 model often predicts an ITB, but its radial location is often too far inside the plasma, or shrinks as the simulations proceed in time. Consequently, the central temperatures at the end of the simulations during the high performance phase are usually underestimated. It is worth noting that GLF23 features in general better predictions of the Te and Ti profiles outside the ITB than the other models studied. Achieving the quantitative capability to predict the multi-channel ITB dynamics with fully predictive, time-dependent transport simulations has turned out to be extremely challenging.

A new model for the type I ELMy H-mode based on linear ballooning stability theory is presented. The model can be written as a linear differential equation for the amplitude of an unstable ballooning mode and is coupled to a system of transport equations. The differential equation for the ballooning mode amplitude has two terms-one representing the growth rate of the perturbation and one controlling the decay rate of the mode and driving the mode amplitude towards the level of background fluctuations. A critical pressure gradient limit is used to control whether the growth rate differs from zero. When coupled to a JETTO transport simulation, the model qualitatively reproduces the experimental dynamics of a type I ELMy H-mode, including an edge localized mode (ELM) frequency that increases with the external heating power. This paper also discusses why the linear ballooning model, in the first place, produces discrete oscillations when coupled to a transport simulation rather than a stationary state with a slightly enhanced ballooning mode amplitude.