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Hydrogen plasma in interaction with diamond materials

par Régis BISSON - publié le

Hydrogen plasma in interaction with diamond materials :
erosion and negative-ion surface production

Introduction :
The ITER project and its successor DEMO (first fusion based power plant prototype) aim at controlling proton fusion reactions and at producing energy. In these fusion devices, heating and current drive of the plasma are mainly obtained through the injection of high-energy (1-2 MeV) and high-intensity D/H neutral beams originating from neutralized D-/H- negative-ion beams. The standard and most efficient solution to produce high negative-ion current uses cesium (Cs) injection and deposition inside the negative-ion source to enhance negative-ion surface-production mechanisms. However, ITER and DEMO requirements in terms of extracted current push this technology to its limits. Diffusion of cesium inside the accelerator stage of the neutral beam injector (NBI) will complicate the ITER-NBI maintenance, and will lead to severe issues for long-term operation-stability of DEMO NBI.

Objectives :
The first objective of the present project is to find alternative solutions to produce high yields of H-/D- negative-ions on surfaces in Cs-free H2/D2 plasmas. It has been shown at PIIM laboratory that carbon materials are excellent negative-ion enhancer materials. In particular we have shown a huge 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.

Post-doc work :
The work is essentially experimental. The post doc will study negative-ion surface production on diamond, as well as diamond erosion, in a high-density low-pressure hydrogen plasma source. The source is equipped with in-situ surface and plasma diagnostics : TALIF (Two photon Absorption Light Induced Fluorescence) for the measurement of atomic flux, Langmuir probe, mass spectrometry, ellipsometry, XPS (X-Ray Spectrometry), TPD (Temperature Programmed Desorption)... The post doc will mostly work at PIIM laboratory (Marseille, France) with possible experimental campaigns at LSPM (Paris-Nord University) and at DIFFER (The Netherlands) on Magnum PSI device.

Knowledge in plasma science and/or surface science is required. The candidate must have experience in LIF measurements and surface analyses (preferentially ellipsometry or XPS …).

References :
•A Ahmad, J Dubois, T Pasquet, M Carrère, J M Layet, J B Faure, G Cartry, P Kumar, T Minéa, S Mochalskyy and A Simonin, Plasma Sources Sci. Technol. 22 (2013) 025006 (15pp)

•G. Cartry, L. Schiesko, C. Hopf, A. Ahmad, M Carrère, J. M. Layet, P. Kumar, and R. Engeln, Physics of Plasmas 19, 063503 (2012)

•P Kumar, A Ahmad, C Pardanaud, M Carrère, J M Layet, G Cartry, F Silva, A Gicquel and R Engeln, Fast track communication, J. Phys. D : Appl. Phys. 44 (2011) 372002

Contacts :
Institution : Aix Marseille University / CNRS
Laboratory : PIIM, service 241, Centre de St Jérôme, 13397 Marseille Cedex 20
Supervisor : Gilles CARTRY
Phone : 33(0)4 91 28 89 59
e-mail : gilles.cartry
Further information : please contact Gilles Cartry using the email above
Application : please send your CV to Gilles Cartry using the email above