Current collection in a spacecraft Wake Laboratory and computer simulations of space plasmas

Summary form only given. A 3-D Poisson-Vlasov (PV) code, POLAR, has been developed to model the interactions of large spacecraft with low earth orbit (LEO) plasma. POLAR can accept chamber plasma parameters but cannot account for many other differences between chamber and space conditions. These include wall effects, ion beam anisotropy and divergence, and electron deficiency and trapping. A 2-D-3V axisymmetric PV code (MACH) that can perform both chamber and space simulations is also used to bridge the gap between POLAR and the laboratory results. Two types of laboratory experiments have been performed to investigate the steady-state and temporal aspects of the current collection problems. The first experiment utilizes an ion thruster to produce a flowing plasma in a large vacuum chamber in order to minimize the effects of chamber walls and charge exchange cold ions. The second experiment employs a pulsed plasma stream to gain insights into the time-dependent effects which cannot yet be modeled by existing computer codes. The ion current collection process was investigated, with attention focused on the interplay between the details of the wake potential profile, the thermal energy spread of the flowing ions, and the surface effects of the body at high field conditions.