Control of the magnetic field configuration in the MITICA Neutral beam injector

MITICA is a prototype of the Heating Neutral Beam (HNB) Injectors for ITER [1]. The MITICA scientific objective is to validate the design and optimize the operating performances of the injector before installation on ITER. The magnetic field configuration in the injector is critical for obtaining the required efficiency and beam optics. In order to quickly achieve the optimal operating condition, it is highly advisable to provide a flexible control of the most critical features of the magnetic field, without opening the vacuum vessel. The possibility of introducing an independent variation of the magnetic field in the plasma source and in the accelerator has been analyzed and a feasible solution proposed, based on small lateral coils. The possibility of recreating the expected stray magnetic field conditions of the ITER HNB was already foreseen in the past by using a further set of external coils, whose design has been revised and updated. The paper describes the rationale and the magnetic design optimization of these systems.