Magnetic self‐field effects on current collection by an ionospheric bare tether

It was recently suggested that the magnetic field created by the current of a bare tether strongly reduces its own electron‐collection capability when a magnetic separatrix disconnecting ambient magnetized plasma from tether extends beyond its electric sheath. It is here shown that current reduction by the self‐field depends on the ratio L * / L t parameterizing bias and current profiles along the tether ( L t ≡ tether length, L * ≡ characteristic length gauging ohmic effects) and on a new dimensionless number K s involving ambient and tether parameters. Current reduction is weaker the lower K s and L * / L t , which depend critically on the type of cross section: K s varies as R 5/3 , h 2/3 R , and h 2/3 × 1/4 width for wires, round tethers conductive only in a thin layer, and thin tapes, respectively; L * varies as R 2/3 for wires and as h 2/3 for tapes and round tethers conductive in a layer ( R ≡ radius, h ≡ thickness). Self‐field effects are fully negligible for the last two types of cross sections whatever the mode of operation. In practical efficient tether systems having L * / L t low, maximum current reduction in case of wires is again negligible for power generation; for deorbiting, reduction is <1% for a 10 km tether and ∼15% for a 20 km tether. In the reboost mode there are no effects for K s below some threshold; moderate effects may occur in practical but heavy reboost‐wire systems that need no dedicated solar power.