Topic/Type: 1.2 Fusion Plasmas (magnetic & inertial confinement), Poster

ONIX - 3D PIC Modeling of the negative ion extraction from a plasma source.

S. Mochalskyy, A. Lifschitz, T. Minea, G. Maynard

Laboratoire de Physique des Gaz et des Plasma, CNRS-Universit? Paris Sud 11,

Negative ion (NI) plasma sources are used for several applications requiring NI beams. Typically, the extraction of NI from such sources is limited by the space charge built in front of the aperture. Moreover, electrons are co-extracted together with the NI. To avoid electrons to leave the plasma, magnetic filters are usually placed in front of the aperture inducing anisotropy into the system.
The lack of symmetry of the extraction region make necessary the use of full three dimensions (ED) modeling. In addition to that, the low density of the plasma and the low pressure in this type of source prevent the application of the fluid approach.
ONIX (Orsay Negative Ion eXtraction) full 3D (3 space - 3 velocity) Particles-in-Cell (PIC) electrostatic code has been developed in order to investigate the transport of the NI and of electrons in the extraction region. In particular, we want to study the features of the negative ion extracted from the NI plasma source prior to the entry into the accelerator. Once accelerated, the NI high energy beam is neutralized and depleted of its extra-electrons and is further injected into the Tokamak core to heat heavy particle and support the fusion plasma current.
ONIX deals with the complex boundary geometry of the aperture corrected in the problematic points approaching the case of the ITER proposed design [1] is considering he crossed structure of the magnetic field that is applied to trap and deflect electrons.
Results obtained from this code will be presented. They concern the 3D trajectories of the D- ion source in the extraction region with different plasma parameters, the NI current and spatial distribution are given by the code as well asthe NI and electron current density profiles together with their ratio for various local magnetic field configurations. These results have been compared with the experimental data from the IPP Garching[1].

This work is done in the frame of ANR ITER-NIS Grant found by the French Government and it is partially supported by the French F?d?ration de Recherche sur la Fusion Magn?tique.

[1] E. Speth, H.D. Falter, P. Franzen, U. Fantz, M. Bandyopadhyay, S. Christ, A. Encheva, M. Froschle, D. Holtum, B. Heinemann,W. Kraus, A. Lorenz, Ch. Martens, P. McNeely, S. Obermayer, R. Riedl, R. Suss, A. Tanga, R. Wilhelm and D.Wunderlich, Overview of the RF source development programme at IPP Garching, Nuclear Fusion 46, 2006