A model is presented to numerically simulate the time-dependent interaction of satellites with space plasma. The approach is based on a fully kinetic description of the plasma using particle in cell modeling for all plasma species with physical charges and masses. The model also relies on a discretization of space with an unstructured tetrahedral mesh that is capable of representing complex boundaries and realistic spacecraft geometries. The code solves for the self-consistent electric fields, given calculated volume charges and charge deposition on the various satellite components. The model is purely electrostatic, but it does account for the effects of a possible constant and uniform background magnetic field.

Five spacecraft-plasma models are used to simulate the interaction of a simplified geometry Solar Probe Plus (SPP) satellite with the space environment under representative solar wind conditions near perihelion. By considering similarities and differences between results obtained with different numerical approaches under well defined conditions, the consistency and validity of our models can be assessed. The impact on model predictions of physical effects of importance in the SPP mission is also considered by comparing results obtained with and without these effects. Simulation results are presented and compared with increasing levels of complexity in the physics of interaction between solar environment and the SPP spacecraft. The comparisons focus particularly on spacecraft floating potentials, contributions to the currents collected and emitted by the spacecraft, and on the potential and density spatial profiles near the satellite. The physical effects considered include spacecraft charging, photoelectron and secondary electron emission, and the presence of a background magnetic field. Model predictions obtained with our different computational approaches are found to be in agreement within 2% when the same physical processes are taken into account and treated similarly. The comparisons thus indicate that, with the correct description of important physical effects, our simulation models should have the required skill to predict details of satellite-plasma interaction physics under relevant conditions, with a good level of confidence. Our models concur in predicting a negative floating potential Vfl∼−10V for SPP at perihelion. They also predict a “saturated emission regime” whereby most emitted photo- and secondary electron will be reflected by a potential barrier near the surface, back to the spacecraft where they will be recollected.

The first fully two-dimensional eigenmode analysis of the trapped-ion instability in an axisymmetric toroidal geometry is presented. The poloidal structure is taken into account by Fourier-expanding the perturbed electrostatic potential, φ, in ϑ. Assuming that the perturbation varies mildly over a typical ion-banana-width, ρbi, each poloidal harmonic is expressed as a truncated Taylor series in the minor radius to account for the radial structure. The resulting set of coupled ordinary second-order differential equations is solved numerically by the method of finite elements. The formalism is also applicable to the radially local and one-dimensional radial approximations. Results obtained in these limits are presented and found to be in reasonable agreement with previous calculations. In low shear plasmas, the full two-dimensional calculation is in qualitative agreement with the one-dimensional radial approximation. However, for higher shear the two-dimensional calculation yields a somewhat different picture for the radial structure of the instability. The analysis presented is limited to long radial wavelength and electrostatic perturbations.

Kinetic simulations are used to compute current characteristics of finite-length cylindrical probes, with particular attention to end effects. Currents collected per unit lengths, as a function of distance to the ends, are calculated and fitted to empirical analytic functions. These fits, in turn, can be interpolated and used to predict probe characteristics; that is, collected current as a function of applied voltage, for a broad range of physical parameters of relevance to laboratory and space plasma.