[en] The CREATE-L linearized plasma response model can simulate the plasma current, position and shape responses to external coil currents and internal physical variations, also in the presence of 3D conducting structures whose eddy currents cannot be neglected. It has already been validated on existing tokamaks (TCV, FTU) and applied to tokamak under design (ITER) in order to investigate their control system capabilities. On these devices it has also allowed the design of high-order controllers. This paper presents the extension of the CREATE-L model to reversed field pinch (RFP) plasmas. The validation of this new model has been carried out against experimental data from RFX, the largest RFP machine

[en] The maximum allowable vertical displacement which can be recovered by the magnetic control system is a fundamental quantity for tokamak magnetic control (Gribov 2015 Nucl. Fusion 55 073021). This figure of merit is usually defined relying on a mass-less assumption, i.e. the reaction currents in wall structures are considered to vary in order to guarantee MHD equilibrium during the plasma perturbation. Recently we examined the consequences of considering also non-equilibrium perturbations of the vertical position via a simplified rigid filament model (Isernia 2023 Plasma Phys. Controlled Fusion 65 105007). In this case the reaction currents in wall structures are not determined anymore by the MHD equilibrium constraint during the perturbation. We illustrate the mapping of initial conditions between the full dynamic and the reduced mass-less model, emphasizing the role of the mass-less assumption on the definition of maximum allowable displacement. Moreover we show that the ratio between the perturbation time of the vertical position and the electromagnetic time of the unstable mode in the quasi-static limit ∆t/τ_u governs the intensity of reaction currents at the end of the perturbation, hence the overall perturbation of the unstable mode.

[en] This paper presents the features and the performance of the Joint European Torus (JET) plasma response models based on an upgraded version of the CREATE-L code. It takes into account a number of aspects, including an equivalent axisymmetric model of the iron core and the eddy currents induced in the passive structures. The input quantities are the poloidal field circuit currents (or voltages) and two parameters related to the plasma current density profile. The output quantities include the signals provided by the magnetic diagnostic system of JET (fields, fluxes and flux differences) as well as plasma current and shape. The equivalent axisymmetric model of JET and the plasma response models have been assessed on a set of JET pulses, by comparing the simulated open loop response of the magnetic measurements and the plasma shape to the experimental measurements. The electromagnetic analysis shows that the axisymmetric model of the iron is satisfactory. The linearized plasma response model provides a reliable base for the design and the assessment of a new current, shape and position control system in JET, and accurately predicts the growth rate of the vertical instability of an elongated JET plasma

[en] This paper describes the development and experimental validation of a simulation model for the design of FTU plasma radial position and current controllers. These controllers have been designed to be tested experimentally on the FTU tokamak. The results predicted in simulation were actually delivered during FTU operation, in two different discharges

[en] Although linear response models are useful for feedback controller design, their linear time-invariant properties cannot simulate the evolution of a full plasma discharge. A suitable code for this purpose is DINA, which has now been benchmarked against a complete set of experimental data from TCV control experiments in both the time and frequency domains. Experimental measurements of the plasma equilibrium dynamic response to poloidal field coil voltage variations have recently been performed on the JT-60U tokamak. These results have been compared with the RZIP rigid current displacement model, previously validated on TCV, but enhanced for the work described

No abstract available

[en] The development of linear model of the present JET (Joint European Torus) electromagnetic system has allowed the design of an optimized Plasma Shape Controller. Quite extreme plasma boundaries (elongation k=1.9 and triangularity <δ>=0.6) are shown to be controllable also in the presence of large variations of the values of poloidal beta (0.1<β_p<0.6) and/or internal magnetic inductance (0.8< l_i<1.4). The developed model gives also an excellent simulation of the growth rate of the experimental vertical disruptions

[en] In this paper the authors analyze the time evolution of a tokamak plasma after the failure of the vertical control system. In this case, the plasma eventually touches the conducting wall and gives rise to currents which flow partly in the wall, partly in the plasma. They show how, under simplifying assumptions, the problem can be analyzed by means of pure electromagnetic formulations. After a brief review of the state of the art in the analysis of this phenomenon, they propose and discuss three alternative Eulerian approaches: an evolutionary equilibrium formulation, a convection-diffusion model and a 3D error-based approach

[en] In the operation of tokamaks, hard-to-predict fast transient events, called disruptions, are often responsible for severe energy deposition on the structures surrounding the plasma. In this paper, first of all we derive an overall energy balance for a disruptive plasma, then we use an evolutionary equilibrium code (CarMa0NL) to reproduce the macroscopic plasma evolution during a disruption of a sample high-aspect-ratio circular plasma, analysing the energy fluxes which take place during the event. We show that the variations of toroidal magnetic energy are compensated by one portion of the Poynting vector flux, and that dissipated heat during the Thermal Quench is mainly related to the loss of internal energy. Moreover, we develop an analytical model providing physical insight on the energy deposition on the wall during the Current Quench, related to the poloidal magnetic energy, in a quantity depending on the time scale of the event compared to the electromagnetic time constants. (paper)

[en] CREATE-L, a simple and reliable linearized plasma response model for the control of the plasma current, position and shape in tokamaks, is presented. The basic assumption made is that the plasma behaviour is described using three degrees of freedom, related to the total plasma current, internal inductance and poloidal beta. The state variables are the coil and plasma currents; the inputs are the applied voltages, whereas poloidal beta and internal inductance play the role of disturbances. The outputs are field and flux values and some basic plasma parameters. The model is tested against non-linear codes and validated via comparison with experimental results. (author)