Optimization of the Accelerators for the ITER Neutral Beam Injector Project

A joint Japan-EU R&D activity is in progress to optimize the accelerator for the ITER NBI. The accelerator baseline design is based on a five grids system which can be adapted to operate with three grids for initial operations at low voltage (500 kV). Moreover, in order to speed up the test of the NBI system at the Test Facility, a negative ion source with extraction voltage up to 100 kV will be operated in parallel to the full injector. In this contribution the three accelerators mentioned above are presented discussing the procedure to optimize the grid geometry in order to assure optimum optics during operation when the grids undergo deformations and thermal stresses due to the particles that hit their surface.