E. Sartori, V. Candeloro, I. Mario, A. Pimazzoni, C. Poggi, G. Serianni, P. Veltri, M. Brombin, R. Casagrande, M. Fadone, N. Marconato, M. Kashiwagi, Kisaki Masashi, H. Nakano, R. Pasqualotto, Basile Pouradier-Duteil, Iacopo Regoli, B. Segalini, Alastair Shepherd, H. Tobari, K. Tsumori, M. Ugoletti, R. Zagórski, B. Zaniol, Edgard Zuin, D. Marcuzzi
Abstract Large plasma sources are employed in negative ion based heating neutral beam injectors for fusion applications. A review of the ITER beam source plasma properties is presented, in comparison with negative ion sources of comparable size, based on the latest experimental measurements from SPIDER and supporting numerical simulations. Spatial investigation of plasma parameters using several diagnostics, including the beam itself, retarding field energy analysers, optical emission spectroscopy, movable and fixed Langmuir probes, is key to understanding the source physics, to support the operation and improve the source performances. The influence of multiple rf-driver configuration on uniformity and the improvement flexibility it provides, as well as the implications of control parameters like filter field and plasma grid bias are examined. Similarities and differences with other giant negative ion sources are discussed to highlight the key physical processes leading to the optimal operation and viable paths for possible improvements of the ITER source design.