Topic/Type: 1.6 Plasma-based devices, Poster

Plasma production in a high power large volume magnetized negative ion source

P. Sarrailh1, 2, G. Fubiani1, 2, 3, G. Hagelaar1, 2, N. Kohen1, 2, J.P. Boeuf1, 2

1 Universit? de Toulouse; UPS, INPT; LAPLACE (Laboratoire Plasma et Conversion d'Energie), Toulouse, France
2 CNRS; LAPLACE; F-31062 Toulouse, France
3 Email: gwenael.fubiani@laplace.univ-tlse.fr

Plasma heating and current drive requirements for the International Thermonuclear Experimental Reactor (ITER) include the use of high power neutral beam (NB) injectors. Each of the ITER NB injectors must deliver about 1 MeV, 17 A (equivalent) of neutral deuterium atoms (i.e., 17 MW) to the fusion plasma. A large volume high power ion source is necessary in order to produce a negative deuterium ion current of ~50A. The source consists in an inductively coupled plasma discharge (driver), an expansion chamber, and a magnetic filter. The production of negative ions in the discharge volume is not sufficient and cesium is deposited on the surfaces (especially on the extracting grid after the magnetic filter) to enhance negative ion production. The role of the magnetic filter is to lower the electron energy in order to enhance negative ion production and survival in the extraction region, and to limit the extracted electron current. The physics involved in such a source is relatively complex and, as a result, providing a precise design requires a substantial modeling effort.

In this paper, we report on recent progress made in the simulation of a high power large volume negative ion source. Typical characteristics of these sources are high plasma density (~1018 m-3), strong neutral depletion, large temperature & plasma potential in the discharge region and a lower density and significant drop in electron temperature in the expansion region due to the magnetic filter field. In addition a large accumulation of negative ions is expected in the extraction region.

Typical simulation results will be presented with emphasis on:
- the existence and consequences of a strong depletion of the neutral density in the source
- the influence of the plasma-wall chemistry on the dissociation degree and on the neutral temperature and (non-Maxwellian) neutral velocity distribution function
- the complex plasma-chemistry and its consequences on the plasma properties (electron temperature, plasma potential, dissociation degree, and relative importance of different ions)
- the charged particle transport in the magnetic filter region

Preliminary comparisons with experiments will be reported.

This work is supported by ANR (National Research Agency) under contract BLAN08-2\_310122, by the ITER Federation and by the French Atomic Energy Commission (CEA).