The ion energy-angle distribution (IEAD) at the wall of a magnetized plasma is of fundamental importance for the determination of the material processes occurring at the plasma-material interface, comprising secondary emissions and material sputtering. Here, we present a numerical characterization of the IEAD at the wall of a weakly collisional magnetized plasma with the magnetic field inclined at an arbitrary angle with respect to the wall. The analysis has been done using two different techniques: (1) a fluid-Monte Carlo method, and (2) particle-in-cell simulations, the former offering a fast but approximate method for the determination of the IEADs, the latter giving a computationally intensive but self-consistent treatment of the plasma behavior from the quasi-neutral region to the material boundary. The two models predict similar IEADs, whose similarities and differences are discussed. Data are presented for magnetic fields inclined at angles from normal to grazing incidence (0°–85°). We show the scaling factors of the average and peak ion energy and trends of the pitch angle at the wall as a function of the magnetic angle, for use in the correlation of fluid plasma models to material models.

Radiofrequency discharges used in industry often have centrally peaked plasma density profiles n(r) although ionization is localized at the edge, even in the presence of a dc magnetic field. This can be explained with a simple cylindrical model in one dimension as long as the short-circuit effect at the endplates causes a Maxwellian electron distribution. Surprisingly, a universal profile can be obtained, which is self-similar for all discharges with uniform electron temperature T e and neutral density n n. When all collisions and ionizations are radially accounted for, the ion drift velocity toward the wall reaches the Bohm velocity at a radius which can be identified with the sheath edge, thus obviating a pre-sheath calculation. For non-uniform T e and n n , the profiles change slightly but are always peaked on axis. For helicon discharges, iteration with the HELIC code for antenna-wave coupling yields profiles consistent with both energy deposition and diffusion profiles. Calculated density is in absolute-value agreement with experiment. V

In this work, we present a newly constructed UxOy reaction mechanism that consists of 30 reaction channels (21 of which are reversible channels) for 11 uranium molecular species (including ions). Both the selection of reaction channels and calculation of corresponding rate coefficients is accomplished via a comprehensive literature review and application of basic reaction rate theory. The reaction mechanism is supplemented by a detailed description of oxygen plasma chemistry (19 species and 142 reaction channels) and is used to model an atmospheric laser ablated uranium plume via a 0D (global) model. The global model is used to analyze the evolution of key uranium molecular species predicted by the reaction mechanism, and the initial stage of formation of uranium oxide species.

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Determination of the mechanisms underlying the growth of tungsten fuzz is an important step towards mitigation of fuzz formation. Nanostructured tungsten was produced on resistively heated tungsten wires in a helicon plasma source (maximum flux of 2.5 × 10 21 m −2 s −1). Asymmetry in the setup allows for investigation of temperature and flux effects in a single sample. An effort at elucidating the mechanism of formation was made by inspecting SEM micrographs of the nanostructured tungsten at successive fluence steps of helium ions up to a fluence of 1 × 10 27 m −2. To create these micrographs a single tungsten sample was exposed to the plasma, removed and inspected with an SEM, and replaced into the plasma. The tungsten surface was marked in several locations so that each micrograph is centred within 200 nm of each previous micrograph. Pitting of the surface (diameter 9.5 ± 2.3 nm, fluence (5 ± 2)×10 25 m −2) followed by surface roughening (fluence (9 ± 2) × 10 25 m −2) and tendril formation (diameter 30 ± 10 nm, fluence (2 ± 1) × 10 26 m −2) is observed, providing evidence of bubble bursting as the mechanism for seeding the growth of the tungsten fuzz.

Partially ionized gas discharges used in industry are often driven by radiofrequency (rf) power applied at the periphery of a cylinder. It is found that the plasma density n is usually flat or peaked on axis even if the skin depth of the rf field is thin compared with the chamber radius a. Previous attempts at explaining this did not account for the finite length of the discharge and the boundary conditions at the endplates. A simple 1D model is used to focus on the basic mechanism: the short-circuit effect. It is found that a strong electric field (E-field) scaled to electron temperature T e , drives the ions inward. The resulting density profile is peaked on axis and has a shape independent of pressure or discharge radius. This "universal" profile is not affected by a dc magnetic field (B-field) as long as the ion Larmor radius is larger than a.

For successful commercial adaptation of the ß-EDM (micro electro-discharge machining) process, there is a need to increase the process efficiency by understanding the process mechanism. This paper presents a model of the plasma discharge phase of a single discharge ß-EDM event in deionized water. The plasma discharge is modeled using global model approach in which the plasma is assumed to be spatially uniform, and equations of mass and energy conservation are solved simultaneously along with the dynamics of the plasma bubble growth. Given the input discharge voltage, current and the discharge gap, complete temporal description of the ß-EDM plasma during the discharge time is obtained in terms of the composition of the plasma, temperature of electrons and other species, radius of the plasma bubble and the plasma pressure. Eor input electric field in the range of 10-2000 MVIm and discharge gap in the range of 0.5-20 ßm, timeaveraged electron density of 3.88 x 10^' 'm^^ -30.33 x 10^''m~^ and time-averaged electron temperature of 11,013-29,864 K are predicted. Experimental conditions are simulated and validated against the spectroscopic data from the literature. The output from this model can be used to obtain the amount of heat flux transferred to the electrodes during the ß-EDM process.

The long-standing problem of plasma diffusion across a magnetic field (B-field) is reviewed, with emphasis on low-temperature linear devices of finite length with the magnetic field aligned along an axis of symmetry. In these partially ionized plasmas, cross-field transport is dominated by ion-neutral collisions and can be treated simply with fluid equations. Nonetheless, electron confinement is complicated by sheath effects at the endplates, and these must be accounted for to get agreement with experiment.