Ground Experiments and Computer Simulations of Interaction Between Bare Tether and Plasma

The electrodynamic bare tether system shows a promise of efficient electron current collection. Several problems associated with the use of the bare tether were investigated, such as anomalous current collection due to ionization of the neutral gas, negative arcs, and heating by current collection. These phenomena may adversely affect the control of the tether system. In this paper, we performed ground experiments and numerical simulations. In the positive-bias experiment, the anomalous electron current collection occurred when the tether potential was greater than 170 V in Xe plasma of 3.5 times 10¹² m^-3 density and 2.5 eV temperature with back pressure of 9.7 times 10^-3 Pa. We also performed surface-temperature measurement of the bare tether. The tether was heated by impacting electrons to a temperature higher than 120degC for the tether potential of 270 V and a current of 25 mA/m. In the negative-bias experiment, the tether samples with less conductive fibers or insulator coating arced at negative voltage as low as -200 V.