Generation and acceleration of negative ions in neutral beam injectors for fusion research: status, perspectives and interdisciplinarity

The development of the NBI system at the unprecedented parameters (40 A of negative ion current accelerated up to 1 MV for 1 hour ) for ITER has fostered an intense worldwide R&D effort on negative ion sources. The above mentioned parameters joint to the request of stable and reliable operation has required the realization of a full scale prototype, to be tested and optimized at the Test Facility under completion at the CNR Research Area in Padova (Italy). The key component of the system is the beam source whose performance is strictly dependent on a deep understanding of the mechanisms behind the generation and acceleration of negative ions. Tackling and solving the key issues emerging from the R&D requires competences coming from plasma physics, chemistry and accelerator physics and technology and shows the potential of establishing new ( and sometime unexpected) bridges towards other disciplines This contribution will present the status and the perspectives of the beam source R&D focusing on two aspects : a) the key role of the status of the surfaces for the negative ions generation and for the high voltage holding and b) the emerging complex network of mechanisms underlying the negative ion generation and extractions which has been found suited to interconnections to astrophysics and modern approach to the controllability of complex systems . Finally an alternative innovative concept for a new generation of negative ion sources will be mentioned as an example of how well-established technology from other fields, in this case from space propulsion, can be applied to improve efficiency and reduce complexity of the source.