Current‐induced magnetic field effects on bare tether current collection: A parametric study

Abstract

Abstract. The physical process of current collection by a "bare wire" electrodynamic tether in space is considered. The study uses an improved model that takes into account the resistance of the wire and the magnetic shielding induced by current flow in the tether. The plasma density, ne, electron temperature, Te, tether length, L, tether radius, r w, and the angle of the geomagnetic field to the tether (90ø-o0 were all used as parameters. It is shown, for certain tether configurations and parameter values, that magnetic shielding reduces the collected current. In general, any parametric change that increases tether current, and hence, the strength of the current-induced magnetic field relative to the strength of the electric field between the tether and the ambient plasma, will increase the shielding effect. Tether current is increased directly with tether collection area (which depends on L and rw), plasma conductivity (which depends on n• and T0, and the motional emf along the tether (which increases with L and the angle 90ø-00. It turns out that, as any of these parameters change so as to cause the overall tether current to increase, the overestimate of current that results from ignoring the magnetic shielding effect becomes correspondingly greater. Moreover, it is shown that a tether system in the thruster (or motor) mode suffers greater current reduction from magnetic shielding than does the same tether deployed in the generator mode. Finally, it is shown that, for certain tether system configurations combined with particular values of the governing plasma parameters, current-induced magnetic shielding can significantly reduce the collected current and, therefore, system efficiency. For example, in the case of an electrodynamic tether system in the thruster mode under conditions of ne= 1.67xl 06 cm -3, a=60 ø, rw=2.5 mm, and Em=34 Wkm, magnetic shielding will reduce the collected current 10% at a point L=0.65 km along the tether (4.3 A instead of 4.8 A) and this increases to more than 40% at L= 1.3km (9.6 A instead of 13.4 A).

Analyses of Bare-Tether Systems as a Thruster for MXER Studies

“…But the tendency still prevails and the magnetic shielding affect is smallest for the 90º angle between the current and ambient magnetic field. In more details this is discussed by Khazanov et al [2000Khazanov et al [ , 2001. Sanmartin and Estes [2002] proposed a similar model of magnetic shielding as Khazanov et al [2000Khazanov et al [ , 2001 with two changes.…”

“…The reason for such different role of magnetic shielding for these two orbits is discussed below. Results of this study are based on the model of magnetic shielding of Khazanov et al [2000Khazanov et al [ , 2001. Below we present the comparison of this model with the model of magnetic shielding developed by Sanmartin and Estes [2002].…”

“…It can be assumed that the plasma sheath and the boundary between the closed and open regions of magnetic field coincide, if their lengths are equal. Therefore, for that part of the tether where the length of the plasma sheath is larger than the length of the separatrix, the collected current can be calculated as OML current [Khazanov et al, 2000[Khazanov et al, , 2001. In the opposite case the current should be calculated from the thermal flux.…”

“…Different parameters describing tether performance, such as system acceleration and efficiency can be calculated, if the current distribution along the tether at the satellite trajectory is known. Below we present the results of current calculation along the expected trajectory of the MXER tether for wire and tape tethers with different cross-sections, and discuss the magnetic shielding effects based on the results of Khazanov et al [2001], Sanmartin and Estes [2002] papers, and the results of these calculations.…”

A review of electrodynamic tethers for science applications

“…The field due to the tether own current might reduce current collection. Strong redaction would roughly occur at tether points where some average radius r* of a magnetic separatrix modifying field topology in the cross-section plane exceeds the sheath radius r sh [15] …”