Current collection to long conductors with wide geometries for bare electrodynamic tether applications: A laboratory update
We describe chamber tests of simulated electrodynamic tethers (EDTs) of different geometries operating in a dense, high-speed plasma. The geometries tested and described here were cylindrical and flat-ribbon. 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 (tape width ~ 16 λD) as compared to furthest test distances (tape width ~ 6 λD). 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 data at a potential that is near 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 near that expected 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 starting near the ion beam energy.
