The near-field plume region of Hall-effect thruster is investigated using a three-dimensional Particle-in-Cell/Monte Carlo collision (PIC-MCC) model. A detailed electron-surface interaction model has been implemented on the thruster exit plane. Results show the important role of magnetic field in the first 4 cm and of the azimuthal fluctuation together with asymmetry driven by the cathode and with the plasma-surface interaction on the exit plane.

The deconvolution of temperature dependent rate coefficients to energy dependent cross sections is accomplished by using a nonlinear optimization technique. The suggested method is successfully applied to atom-molecule and molecule-molecule dissociation processes in hydrogen.

A Graphics Processing Unit (GPU)-CUDA C and (Multi-core)-OpenMP versions of the Reaction Ensemble Monte Carlo method (REMC) are presented. The REMC algorithm is a powerful tool to investigate the equilibrium behavior of chemically reacting systems in highly non-ideal conditions. Both the GPU and the Multi-core versions of the code are particularly efficient when the total potential energy of the system must be calculated, as in the constant-pressure systems. Results, obtained in the case of Helium plasma at high pressure, show differences between real and ideal cases.

The self-consistent production and transport of H- in the extraction region of a hybrid negative ion source is modeled by means of a two-dimensional particle-in-cell/Monte Carlo simulation. The normal coordinate and one parallel coordinate with respect to the plasma grid are considered to analyze the transport of negative ions. Results show that, in order to establish space charge compensation, the extraction of surface-produced negative ions is limited by the flux of positive ions directed toward the plasma grid surface. An electrostatic barrier appears just in front of the wall, reflecting the majority of surface-produced H- and reducing by this their extraction probability to only 8.5%. Results reproduce the experimentally observed influence of the plasma grid bias voltage on the extraction identifying as a key element the presence of a saddle point in the electric potentialdistribution.

More self-consistent injection boundary conditions from the source region have been used in the extraction region model to examine the negative ion formation and transport. Bulk kinetic, plasma-surface, and gas-surface processes have been all included. This work represents a first example of coupling between different models, and it shows the important role of positive ion conversion on plasma grid for the extracted negative ion current.

A two-dimensional particle-in-cell/Monte Carlo collision model has been developed and used to study low electronegative magnetized hydrogen plasma. A configuration characterized by four electrodes is used: the left electrode is biased at Vl 1/4 ?100 V, the right electrode is grounded, while the upper and lower transversal electrodes are biased at an intermediate voltage Vud between 0 and ?100 V. A constant and homogeneous magnetic field is applied parallel to the lateral (left/right) electrodes. It is shown that in the magnetized case, the bulk plasma potential is close to the transversal electrodes bias inducing then a reversed sheath in front of the right electrode. The potential drop within the reversed sheath is controlled by the transversal electrodes bias allowing extraction of negative ions with a significant reduction of co-extracted electron current. Furthermore, introducing plasma electrodes, between the transversal electrodes and the right electrode, biased with a voltage just above the plasma bulk potential, increases the negative ion extracted current and decreases significantly the co-extracted electron current. The physical mechanism on basis of this phenomenon has been discussed.

Kinetic modelling of nonequilibrium flows is described as it applies to hypersonic phenomenology. A Monte Carlo method is described for the study of species separation on shock wave fronts; a Particle in Cell with Monte Carlo Collisions (PIC/MCC) technique is described for the simulation of dust in plasma flows; modelling of nonequilibrium radiation in shock heated gases; implementation of slip models for the description of separation zones occurring in shock- boudary layer interactions.

In this paper we present results of different particle-based models of expansion and extraction regions for the ITER negative ion source. Results show the important role of electron-induced processes (eV excitation and dissociation) and gas-surface and plasma-surface interactions (atom recombinative desorption and ion neutralization) for the production of negative ion precursors. The spatial distribution of neutral and ionized caesium as well as the drag due to the deuterium flow and its re-evaporation from the plasma grid is calculated. The self-consistent two-dimensional electric field distribution in the extraction region allows a better understanding of the transport of surface-produced negative ions towards the orifice. The model delivers an extraction probability of less than 25%.

There are still many missing elements to complete the full understanding of physical mechanisms at the basis of the Hall thruster functioning. The origin of the anomalous electron cross-field transport remains unrevealed, while electron-wall interaction is often studied by local and/or reduced dimensional models. In this study, we attempt a fully kinetic self-consistent 3D particle-based simulation of the Hall-effect discharge. Results show the presence of multi-dimensional sheath structures in the acceleration region characterized by azimuthal modulation and axial transition from classical to reversed sheath.

By means of a self-consistent three-dimensional particle model of the source-extraction transition region of a surface-produced negative ion source, the characteristics of negative ion transport have been revealed. It is purely electrostatic and collision-induced (charge exchange with atoms) and magnetic-induced (gyration around filter field) transport contributions play no relevant role for the H- transport. In fact, the key point is the penetration of the EG field inside the source, which helps removing negative ions produced on the surface. This study suggests that the best PG shape is characterized such to allow the extraction EG field from attaching the surface from where H- are produced and that the best aperture size is directly related to this particular shape.

A self-consistent three-dimensional particle-based model of the source extraction-acceleration transition region of a surface-produced negative ion source is developed. Some considerations are advanced on the characteristic of negative ion transport: it is purely electrostatic while collision-induced (charge exchange with atoms) and magnetic-induced (ion gyration around the filter field) transport contributions play no relevant role in H-extraction. In fact, the calculations presented here indicate that the key point is the penetration of the extraction grid field inside the plasma grid collar and the source region, which helps in removing the negative ions produced on the surface. This study suggests that the best plasma grid shape is characterized so as to allow the extraction field to arrive directly on the surface-emitting H- ions and that the best aperture size is directly related to the particular shape used.