DEVELOPMENT OF A FIXED POSITION FILAMENTARY PLASMA MODEL BASED ON THE CURRENT MOMENT DESCRIPTION

In tokamak devices, the accuracy and the robustness of the control system rely on the precise and quick identification of plasma geometry, whose description is based on the magnetic configuration produced by the plasma and the poloidal coils. For this purpose, at JET a code is employed that computes the flux map in real time simply by interpolating the magnetic measurements, using a model only for some of the active coils. In this work a simple plasma model has been developed in order to help the fitting procedure and to improve the boundary reconstruction while keeping high computational speed. The plasma presence is taken into account by using a set of filamentary currents placed inside the vacuum vessel. The filament position remains fixed during the plasma evolution, which allows calculating the Green’s functions off-line, and the current moment method has been chosen to determine the amount of current flowing in the filaments. The moments describe some features of the plasma shape using the internal current distribution, thus separating internal field sources from external ones. The filaments will therefore preserve the consistency with the physics and provide at the same time a linear formulation that can be expressed in matrix product form, which makes this solution particularly suitable for the real time implementation. With reference to the JET tokamak, a wide range of configurations has been tested verifying the reliability of the methodology and the correctness of the filament model.