Characterization of a Plasma Source for Ground-Based Simulation of LEO Plasma Conditions

We characterize the parameters of the flowing argon plasma produced by a 16-cmdiameter plasma source utilizing a transverse magnetic filter to reduce electron temperature while maintaining the quasineutrality of the flowing plasma, as a function of the operating parameters of the source: discharge voltage, discharge current, and gas flow rate/neutral background pressure. We evaluate the plasma parameters against the desirable characteristics of a low-Earth-orbit (LEO) plasma simulator, namely, cold particle distributions with a Mach number (relative to the ion acoustic speed of the plasma) characteristic of LEO spacecraft. We measure electron temperatures from 0.5 to 0.8 eV and ion temperatures from 0.7 to 1.3 eV, with greater than 95% of the ions and 70 to 80% of the electrons in the thermal distribution. The flow is characterized by Mach numbers from 2.7 to 3.9, with Debye lengths in the plasma as low as 0.4 cm. Using a suite of two instruments, a traditional planar retarding potential analyzer (RPA) and a unique miniature electrostatic analyzer (MESA) “laminated analyzer” developed as a rugged, mass-producible survey instrument for spacecraft, we are able to validate the measurements of the former instrument and demonstrate the utility of the latter device in a realistic plasma environment. Based on the behavior of the source with the measurements we have made to date (such as the direct proportionality of downstream plasma density to the discharge current in the source) we see a clear path forward to further improvements in the source as a viable LEO plasma simulator.