Current Collection to Long, Thin Probes in a Dense High-speed Flowing Plasma

We describe chamber tests of simulated electrodynamic tethers (EDTs) of different geometries operating in a dense, high-speed plasma. The geometries tested were cylindrical, flat-ribbon, and sparse-ribbon or mesh. Several important conclusions that can be drawn from the tests are as follows: the currents collected by cylinder are close to what would be predicted via orbital-motion-limited (OML) current collection theory. The tape tether had comparable current levels to a theoretical equal area OML cylinder collector. However, I-V behavior clearly is different at nearest distances (w 15 10 tape width) as compared to fixthest test distances (w 6 10 tape width). The tape tether did better than a theoretical equal mass solid cylinder. A “knee” in the I-V curves can be seen in the tape/mesh data at a potential that is just above the estimated energy of the incoming beam of ions, at least for the closest distances where Debye length is smallest. Below this knee the current increases rapidly as voltage is increased. Above the knee the current increases at a rate one might expect from OML current-collection models depending on the relative width. This likely is an example of high-speed plasma flow effect. Perpendicular tape orientation performed slightly better than parallel.