Current‐produced magnetic field effects on current collection

Khazanov, G. V.; Stone, N. H.; Krivorutsky, E. N.; Liemohn, Michael W.

doi:10.1029/2000ja000039

Cited by 10 publications

(18 citation statements)

References 15 publications

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“…Both K s and L * depend critically on the type of tether cross section: We find K s ∝ R 5/3 for wires and K s ∝ h 2/3 R for thin tapes or round tethers conductive only in a thin layer, with h thickness of tape or layer (for a tape R is the equivalent radius, 1/4 width , of collection theory [ Sanmartín and Estes , 2001]); length L * varies as R 2/3 for wires and as h 2/3 for tapes and round tethers conductive in a layer. As a result, B s ‐effects are fully negligible for the last two types of cross‐sections, and need only be discussed for wires, which were the tethers studied by Khazanov et al [2000, 2001].…”

Section: Discussionmentioning

confidence: 99%

“…The criterion for strong self‐field effects requires the plasma sheath to lie inside the separatrix in some average sense. Khazanov et al [2000] first assumed no electron collection under condition r sh + l ef < ar *, with full collection otherwise; here a is some appropriate coefficient, and r sh and l ef (≪ r sh ) are sheath radius and a local gyroradius, which accounts for a small thermal flux accross the separatrix. They later refined the criterion by estimating how collection is reduced but not fully suppressed under the weaker condition with full collection otherwise [ Khazanov et al , 2001].…”

Section: Magnetic‐separatrix Versus Electric‐sheath Conditionmentioning

confidence: 99%

“…Although K s does also increase with R , the way it does depends on the type of cross section. Cross sections other than the fully conductive circle (wire) considered by Khazanov et al [2000, 2001] make for weaker B s effects. For a wire, for a round tether conductive only on a thin outer layer of thickness h , and for a thin tape of thickness h the last bracket of yields respectively ( R eq = 1/4 tape width).…”

Section: A Self‐field Parametermentioning

confidence: 99%

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

Sanmartin

Estes

2002

J.‐Geophys.‐Res.

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[1] 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 Â 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.INDEX TERMS: 7807 Space Plasma Physics: Charged particle motion and acceleration; 7815 Space Plasma Physics: Electrostatic structures; 7853 Space Plasma Physics: Spacecraft/atmosphere interactions; 7855 Space Plasma Physics: Spacecraft sheaths, wakes, charging; KEYWORDS: ionospheric tethers, bare tethers, magnetic self-field of tethers, magnetic effects on current collection, orbital-motionlimited current, magnetic topology Citation: Sanmartin, J. R., and R. D. Estes, Magnetic self-field effects on current collection by an ionospheric bare tether,

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Section: Discussionmentioning

confidence: 99%

Section: Magnetic‐separatrix Versus Electric‐sheath Conditionmentioning

confidence: 99%

Section: A Self‐field Parametermentioning

confidence: 99%

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

Sanmartin

Estes

2002

J.‐Geophys.‐Res.

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“…More to the point, however, tether signal detection would require modulating the current in the tether circuit, the Alfvén-radiation impedance being weak in the case of a steady tether current. 1 The magnetic self-field of the tether 3 would then result in a background magnetic field time modulated ͑at some frequency mod ).…”

Section: Discussion Of Resultsmentioning

confidence: 99%

“…2 Nonlinear effects, which should appear at the near wave front, might be affected by the magnetic self-field generated by the very current of the tether. 3 An Airy-like linear structure is a feature common in fronts of dispersive waves radiated by a moving source, as with ion-acoustic waves excited by a charged body moving mesothermally in a low ion-temperature plasma; the nonlinear wave front is then described by the Korteweg-de Vries equation. 4 In the case of Alfvén waves, some strong nonlinear effects are known to be described by the derivative nonlinear Schrödinger ͑DNLS͒ equation, 5 which admits soliton solutions 6 and has proved amenable to the inverse scattering method for obtaining general solutions.…”

Section: Introductionmentioning

confidence: 99%

Hard transition to chaotic dynamics in Alfvén wave fronts

et al. 2004

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The derivative nonlinear Schrödinger ͑DNLS͒ equation, describing propagation of circularly polarized Alfvén waves of finite amplitude in a cold plasma, is truncated to explore the coherent, weakly nonlinear, cubic coupling of three waves near resonance, one wave being linearly unstable and the other waves damped. In a reduced three-wave model ͑equal dampings of daughter waves, three-dimensional flow for two wave amplitudes and one relative phase͒, no matter how small the growth rate of the unstable wave there exists a parametric domain with the flow exhibiting chaotic relaxation oscillations that are absent for zero growth rate. This hard transition in phase-space behavior occurs for left-hand ͑LH͒ polarized waves, paralleling the known fact that only LH time-harmonic solutions of the DNLS equation are modulationally unstable, with damping less than about ͑unstable wave frequency͒ 2 /4ϫion cyclotron frequency. The structural stability of the transition was explored by going into a fully 3-wave model ͑different dampings of daughter waves, four-dimensional flow͒; both models differ in significant phase-space features but keep common features essential for the transition.

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

Khazanov¹,

Stone²,

Krivorutsky³

et al. 2001

J. Geophys. Res.

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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).

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Current‐produced magnetic field effects on current collection

Cited by 10 publications

References 15 publications

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

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

Hard transition to chaotic dynamics in Alfvén wave fronts

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

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