Adequate modeling of the plasma plume expansion is paramount for the study of the IBS concept. For the purposes of this preliminary analysis, self-similar models (SSM) exhibit the best trade-o between accuracy and complexity, and retain all the core physics of interest.
SSM models provide a good estimation of the plasma plume properties in the far field, which is the region of interest in the plasma-debris interaction. For their simplicity and accuracy, these models are under active investigation in the Space Propulsion and Plasma Team of the Carlos III University (EP2-UC3M).
Consider an axisymmetric plasma plume expanding into vacuum, generated by an ion engine or Hall effect thruster, consisting of singly-charged, highly-supersonic ions and isothermal electrons of temperature Te. Beyond a first region where the plasma plume starts to form, where beam non-uniformities, collisions, temperature gradients, plasma electric currents, and residual thruster electromagnetic fields can dominate, the plasma jet is smooth and expands under the action of its own residual pressure and fields. Experiments show that this near-field region spans only a few thruster radii from the exit, meaning that the plasma reaching the debris is well into the far-field plume.