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This work represents the first attempt to model the full-size ITER negative ion source prototype including expansion, extraction and part of the acceleration regions keeping the resolution fine enough to resolve every single aperture of the extraction grid. The model consists of a 2.5-dimensional Particle-in-Cell/Monte Carlo Collision representation of the plane perpendicular to the filter field lines. Both the magnetic filter and electron deflection fields have been included. A negative ion current density of j H − = 500 A m − 2 produced by neutral conversion from the plasma grid is used as fixed parameter, while negative ions produced by electron dissociative attachment of vibrationally excited molecules and by ionic conversion on plasma grid are self-consistently simulated. Results show the non-ambipolar character of the transport in the expansion region driven by electron magnetic drifts in the plane perpendicular to the filter field. It induces a top-bottom asymmetry detected up to the extraction grid which in turn leads to a tilted positive ion flow hitting the plasma grid and a tilted negative ion flow emitted from the plasma grid. As a consequence, the plasma structure is not uniform around the single aperture: the meniscus assumes a form of asymmetric lobe and a deeper potential well is detected from one side of the aperture relative to the other side. Therefore, the surface-produced contribution to the negative ion extraction is not equally distributed between both the sides around the aperture but it come mainly from the lower side of the grid giving an asymmetrical current distribution in the single beamlet.

Plasma chemistry of main Earth atmospheric components in VLEOs is implemented in a hybrid 2D axisymmetric simulation code to assess the air-breathing concept in an electrodeless plasma thruster. Relevant electron-heavy species collisions for diatomic molecules, and atom associative wall recombination into molecules are included. Simulations are run by injecting 1 mg/s of Xe, N2 and O independently for powers between 10 and 3000 W. The performances and trends of plasma response for N2 and O are similar to Xe but displaced to higher powers. Since they have lighter elementary masses, a higher plasma density is generated and more electrons need to be heated. At optimum power, the thrust efficiency for N2 and O surpasses that of Xe, which is caused by the excess of neutral re-ionization and the associated inelastic and wall losses. Additional simulations are run injecting 50/50 of N2/O to study the thruster operation for propellant mixtures, and the performances are found to be linear combinations of those of each propellant in the absence of collisions between heavy species. Injection of O2 is also studied for the impact of the possible associative recombination of O at the intake walls, and the performances are found similar to those of O due to the strong molecular dissociation inside the thruster.

In NIO1, a compact H - ion source installed at RFX operated in continuous mode, gas conditioning was needed to improve results in Cs-free regimes (up to a current density about 25 or 30 A/m 2 ). Installation of a cesium oven gave an additional increase of current, progressively limited also by a rapid overcesiation: we observed an average density about 50 A/m 2 (with a peak of 67 A/m 2 ). Obtained beam optics is briefly compared with simulations and previous results in the Cs-free regime in similar conditions (as source voltage, often set below or equal 11 kV). In both regimes, central beamlet apparent density is larger, possibly because of a narrow bias plate mask, now enlarged. Further improvements for Cs-based regime include a moderate oven reservoir temperature, careful tuning and a substantial increase of beam voltage, and power handling capability.

A theoretical investigation of electron-D2 resonant collisions - via the low lying and the Rydberg states of D2- - is presented for vibrational excitation, dissociative electron attachment and dissociative excitation processes by using the local-complex-potential approach. Full sets of vibrationally resolved cross sections, involving the ground electronic state - X 1{\\Sigma}+g - and the first two electronic excited states - b 3{\\Sigma}+u and B 1{\\Sigma}+ u - of the D2 molecule, are given for fusion plasma applications in their technologically relevant partially dissociated, detached divertor regimes. In particular, transitions between electronic excited states are also considered. Comparisons are made with cross sections present in the literature, where available

This perspective paper deals with an overview of particle-in-cell / Monte Carlo collision models applied to different plasma-propulsion configurations and scenarios, from electrostatic (E x B and pulsed arc) devices to electromagnetic (RF inductive, helicon, electron cyclotron resonance) thrusters, with an emphasis on plasma plumes and their interaction with the satellite. The most important elements related to the modeling of plasma-wall interaction are also presented. Finally, the paper reports new progress in the particle-in-cell computational methodology, in particular regarding accelerating computational techniques for multi-dimensional simulations and plasma chemistry Monte Carlo modules for molecular and alternative propellant

The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts - Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion energy flux to the thruster channel surface as compared to SPT. The erosion yields for dielectric discharge channel walls of SPT and HEMP thrusters were calculated with the binary collision code SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material per hour was observed. For HEMP, thruster simulations have shown that there is no erosion inside the dielectric discharge channel.