The injection of energetic neutral deuterium atoms will be one of the major heating methods of the ITER plasma. The 1 MeV, 16.5 MW neutral atom beam will be obtained by acceleration and collisional neutralization of negative ions extracted from an inductively coupled low-temperature plasma source. This negative ion source is composed of driver volumes where the RF (radio-frequency) power is inductively coupled to the plasma electrons, an expansion chamber including a magnetic filter, and the extraction grids. In this paper we present the first results of a 2D fluid model of a single-driver prototype of the source, for an H 2 plasma under realistic ITER-relevant conditions. We discuss the general plasma properties: plasma density, electron and neutral particle temperatures, ion composition (H + , H + 2 , H + 3 ), the dissociation degree of H 2 and the effect of the magnetic filter, in a large range of input powers (10-80 kW) and source pressures (0.2-0.8 Pa). Negative ions are not described self-consistently in this first approach. The results show a decrease in the gas density when the plasma is turned on, due to gas heating and to the neutral gas depletion induced by ionization. The low gas density leads to a high electron temperature in the driver, and to the saturation of the plasma density growth with power for pressures below 0.3-0.4 Pa. The H 2 temperature is in the 0.1 eV range while the H temperature is much higher (up to 1 eV) because hydrogen atoms are generated at high energies by the dissociation of H 2 or ion recombination at the wall surface. The simulation results are globally consistent with recent experiments on the negative ion source developed at IPP Garching. Because of the large Hall parameter in the magnetic filter, electron transport across the filter is complex and the ability of a 2D fluid model to grasp this complexity is discussed.

In this paper the electrostatic sheath of a simplified spacecraft is investigated for heliocentric distances varying from 0.044 to 1 AU, using the 3D Particle in Cell (PIC) software Satellite Plasma Interaction System (SPIS). The baseline context is the prediction of sheath effects on solar wind measurements for various missions including the Solar Probe Plus mission (perihelion at 0.044 AU from the Sun) and Solar Orbiter (perihelion at 0.28 AU). The electrostatic sheath and the spacecraft potential could interfere with the low energy (a few tens of eV) plasma measurements, by biasing the particle distribution functions measured by the detectors. If the spacecraft charges to large negative potentials, the problem will be more severe as low energy electrons will not be seen at all. The Solar Probe Plus and Solar Orbiter cases will be presented in details and extended to other distances through a parametric study, to investigate the influence of the heliocentric distance to spacecraft. Our main result is that for our spacecraft model the floating potential is a few volts positive from 1 AU to about 0.3 AU while below 0.3 AU the space charge of the photoelectrons and secondary electrons create a potential barrier that drives the spacecraft potential negative.