New Features of the Traps Code for Accurate 3D Magnetic Field Calculations

The TRAPS code (Trapezes, Rectangles And Plasma Scenario) has been developed in the early 90's to evaluate with great accuracy the maximum magnetic field on the TF (Toroidal Field) system of ITER preliminary design, so-called FEAT (Fusion Energy Advanced Tokamak). TRAPS allowed to take into account the coil trapezoidal cross sections and proved more accurate than the FEM code results at the time. TRAPS code's accuracy comes from the mathematical methods used for the computation of the magnetic field induced by trapezoidal cross sectional conductors (straight segments, circle arcs or full circles). The Biot-Savart law integration is carried out fully analytically in the cross section, and even analytically along the segments. This paper briefly describes these calculations, the way their accuracy was improved, and two recently implemented new features: the modeling of circular cross sectional conductors, like those of ITER TF and CS (Central Solenoid) magnets, by trapezes and rectangles. The new modeling of circular cross sectional conductors was successfully applied on an ITER CS module and on the DEMO TF system, showing significant increase in accuracy for the magnetic field compared with the preliminary massive modeling.