Hydrogen plasma in INteraction with Diamond : EXTReme Ion Production and Low Erosion Desired – H INDEX TRIPLED

The present project is put into the context of the international projects ITER and DEMO aiming at managing nuclear fusion to produce energy. In tokamaks (nuclear fusion reactors), a hot plasma composed of deuterium and tritium nuclei is magnetically confined to achieve fusion. The heating of the plasma is mainly obtained by the injection of high-energy deuterium neutral beams, coming from the neutralization of high-intensity D- negative-ion beams. D- negative-ions are produced in a low-pressure plasma source and subsequently extracted and accelerated. The standard and most efficient solution to produce high negative-ion current uses cesium (Cs) injection and deposition inside the source to enhance negative-ion surface-production mechanisms. However, ITER and DEMO requirements in terms of extracted current push this technology to its limits. The already identified drawbacks of cesium injection are becoming real technological and scientific bottlenecks, and alternative solutions to produce negative-ions would be highly valuable.
The first objective of the present project is to find an alternative solution to produce high yields of H-/D- negative-ions on surfaces in Cs-free H2/D2 plasmas. The proposed study is based on a physical effect discovered at PIIM in collaboration with LSPM, namely the enhancement of negative-ion yield on boron-doped-diamond at high temperature. The yield increase observed places diamond material as the most up to date relevant alternative solution for the generation of negative-ions in Cs-free plasmas. The project aims at fully characterizing and evaluating the relevance and the capabilities of diamond films (intrinsic and doped polycrystalline, single crystal as well as nanodiamond films…) as negative-ion enhancers in a negative-ion source.
The second objective is to investigate diamond erosion under hydrogen (deuterium) plasma irradiation, with two main motivations. First, material erosion could be a limitation of the use of diamond as a negative-ion enhancer in a negative-ion source and must be evaluated. Second, the inner-parts of the tokamaks receiving the highest flux of particles and power are supposed to be made of tungsten, but its self-sputtering and its melting under high thermal loads are still major issues limiting its use. It has been shown in the past by one of the partners that diamond is a serious candidate as an efficient alternative-material for fusion reactors. Therefore, diamond erosion in hydrogen plasmas will also be investigated from this perspective. At the moment when all the efforts are put on tungsten, maintaining a scientific watch on backup solutions for tokamak materials is crucial.
The project associates partners with complementary expertise in the field of plasma-surface interactions on the one hand, and diamond deposition and characterization on the other hand. Furthermore, in order to span the gap between fundamental science and real-life applications, negative-ion surface-production and diamond erosion will be studied in laboratory plasmas (PIIM in collaboration with LSPM ) as well as in real devices (Cybele negative-ion source at IRFM and Magnum-PSI experiment at DIFFER ).



PIIM: Physique des Interactions Ioniques et Moléculaires, Université Aix-Marseille, CNRS
LSPM: Laboratoire des Sciences des Procédés et des Matériaux, CNRS, Université de Paris 13
IRFM: Institut de Recherche sur la Fusion Magnétique, Commissariat à l’Energie Atomique, Cadarache
DIFFER: Dutch Institute For Fundamental Energy Research, The Netherlands