Overview of numerical tools applied to the design of high power beam source for ITER

In order to develop the first Heating and Current Drive Neutral Beam Injector (NBIs) for ITER, a Test Facility has been decided to be built at Consorzio RFX in Padova to test and optimize the system. The test facility will host two experiments: a full size Ion Source (40 A, 100 kV) and a prototype injector capable of operating at full power (40 A, 1 MV for one hour). Due to the very demanding parameters of the NBI system, the project has to deal with several challenging issues as different aspects must be simultaneously optimised, like voltage holding, electrostatic optics of the beam, magnetic field configuration to filter the electrons, power dumped on the accelerator grids and cooling, electrostatic repulsion between beamlets, beamlet aiming, thermo-mechanical deformations, management of power associated to particles escaping the accelerator. The optimisation of the system requires a comprehensive approach, taking into consideration at the same time physics and engineering aspects. A comprehensive set of numerical codes addressing different issues is used, to simulate the electrical fields, the magnetic fields, the beam aiming, the pressure inside the accelerator, the stripping reactions and transmitted/dumped power, the grid operating temperature, stress and deformations and the heat load on the electron dump. The results of these simulations are discussed by comparing different codes and by benchmarking with experimental findings from existing facilities. Finally the procedure is applied to optimise the accelerator of the beam source for ITER, which is described by focusing on the confidence on the solution of the main physical and engineering issues.