SUMMARYThis paper presents two immersed finite element (IFE) methods for solving the elliptic interface problem arising from electric field simulation in composite materials. The meshes used in these IFE methods can be independent of the interface geometry and position; therefore, if desired, a structured mesh such as a Cartesian mesh can be used in an IFE method to simulate 3-D electric field in a domain with non-trivial interfaces separating different materials. Numerical examples are provided to demonstrate that the accuracies of these IFE methods are comparable to the standard linear finite element method with unstructured body-fit mesh.

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A new model is developed for three-dimensional global simulations of plasma flow in an entire subscale ion optics. This model explicitly includes apertures located near the edge of the grid surface and fully accounts for the effects of multiple ion beamlets and geometric asymmetry. This model is based on a new algorithm, the streamline hybrid-grid immersed-finite-element particle-in-cell. This algorithm is capable of achieving the same accuracy as an unstructured body-fit mesh-based particle-in-cell with a faster computational speed. Simulation results are presented to understand the plasma sheath upstream of the screen grid, direct impingement of beam ions, the crossover limit, the perveance limit, and the electron backstreaming onset. Nomenclature e = electron charge F = force vector I = current k = Boltzmann constant m = mass q = charge T = temperature t = time v = velocity vector x = position vector = IFE mesh stretching parameter 0 = electric permittivity of vacuum D = Debye length = charge density = electrostatic potential Subscripts a = accelerator grid b= beamlet cc = center-to-center e = electron g = gap between ion optics grids i = ion, or impingement s = screen grid w = grid wall 0 = upstream plasma condition 1 = downstream plasma condition

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This paper presents a simulation model on electrostatic levitation of lunar dust particles in the lunar terminator region. Full-particle particle-in-cell simulations are carried out using real ion to electron mass ratio to obtain plasma sheath, surface charging, and the transition point of surface electric field. Test particle simulations are carried out to simulate the levitation of dust particles from lunar surface. Results show that the dust levitation condition in the terminator region is sensitively influenced by the ambient plasma condition and surface charging, and the levitation altitude varies significantly even for small changes of the sun elevation angle.Index Terms-Electrostatic levitation of dust particles, fullparticle particle-in-cell (PIC), lunar dust charging, lunar surface charging.