SPIDER, MITICA and company: N-NBI activities at Consorzio RFX

The ITER experiment represents the next step in thermonuclear fusion researches. In order to reach the fusion conditions and to control the plasma configuration, additional heating and current drive is required, which will be provided by two neutral beam injectors (NBIs), each supplying 17MW. The beam particles (hydrogen or deuterium) will be electrostatically accelerated to 1MeV; effective gas-cell neutralisation at such beam energy is possible only for negative ions, which are obtained by caesium-catalysed surface conversion of hydrogen/deuterium atoms. The requirements of ITER NBIs (acceleration to 1MeV of 40A negative hydrogen/deuterium ions) have never been simultaneously attained, so that a dedicated Neutral Beam Test Facility (NBTF) was set up at Consorzio RFX (Italy) also to verify the continuous operation of the NBI for one hour, while respecting stringent requirements in terms of beam optics (divergence <7mrad) and aiming  (within 2mrad). To study and optimise the performances of the ITER NBI, the NBTF includes two experiments: MITICA, the full-scale ITER NBI prototype, and SPIDER, the full-scale prototype of the ITER NBI source with 100keV particle energy. SPIDER aims at anticipating the investigations, particularly concerning source uniformity (1x2m² area), negative ion current density and beam optics, and has just entered into operation. Moreover the small, flexible negative ion source NIO1, based on an RF plasma, is operating at Consorzio RFX since 4 years and some facilities address specific issues like the .
The talk gives an outline of the investigation issues and of the facilities operating at Consorzio RFX. Coupling of radiofrequency to the plasma, voltage holding even in the presence of magnetic fields, distribution of caesium emitted by the caesium oven will be addressed by SPIDER experimentation supplemented by the results of other small facilities specifically devoted to these issues and by the studies carried out in the NIO1 experiment. SPIDER operations will profit from a strong numerical activity, devoted to the simulation of the experimental scenarios, and from refined diagnostic instruments, expected to provide a thorough characterisation of the plasma and the beam. Finally the talk will also present some results of the first experiments in SPIDER, including a preliminary characterisation of the source plasma.