No abstract available

No abstract available

[en] In low Earth orbit, the geomagnetic field B is strong enough that secondary electrons or photoelectrons emitted from spacecraft surfaces have an average gyroradius much smaller than typical dimensions of large spacecraft. This implies that escape of these electrons will be strongly inhibited on surfaces which are nearly parallel to B, even if a repelling electric field exists outside them. This effect is likely to make an important contribution to the current balance and hence the equilibrium potential of such surfaces, making high-voltage charging of them more likely. The authors presents numerically-calculated escaping electron fluxes for these conditions, based on the approximations of uniform fields and Maxwellian emission-velocity distributions. He also presents an analytic curve-fit to the results for the important case of normal electric field (uniformly-charged surfaces). For strong normal electric fields, escape is effectively suppressed only when a surface is parallel to B within a few degrees or less, and this leads to sensitivity effects in attempts to predict auroral-zone spacecraft charging. A nonzero tangential component in the surface electric field can greatly enlarge the range of surface orientations for which escape is suppressed, and can also produce large surface currents. He also proposes a simple approximate method for calculating the space-charge-density distribution of escaping electrons. His results imply that on a mostly dielectric large spacecraft such as Shuttle, local charging, especially on surfaces nearly parallel to B, may occur in ionospheric conditions which do not produce overall charging

[en] In an attractive Coulomb electric field and a uniform magnetic field B, some particle orbits originating at infinite distance undergo many reflections, repeatedly approaching the Coulomb center. The chaotic nature of these orbits is discussed and illustrated by numerical calculations. The divergence of neighboring trajectories is shown to occur mostly in discrete jumps when they pass near the Coulomb center. The appearance of chaotic behavior in this simplified situation suggests that it will also occur when space-charge effects significantly perturb the potential distribution around a current-collecting electrode in a space magnetoplasma

[en] A theory is presented for current collection by electrostatic probes in a collisionless, Maxwellian plasma containing a uniform magnetic field B, where the probes are spheroids or finite cylinders whose axis of symmetry is aligned with B, or disks perpendicular to B. The theory yields upper-bound and adiabatic-limit currents for the attracted particle species. For the repelled species, it yields upper and lower bounds. This work is an extension of existing theory for spherical probes by Rubinstein and Laframboise

[en] The authors propose a mechanism which permits high-voltage auroral zone charging to occur on a large enough mostly dielectric spacecraft, in situations where one would otherwise expect such charging to be suppressed by secondary-electron or photoelectron escape from exposed surfaces. This extends, to lower equivalent temperatures, the range of auroral electron plasma conditions in which one can expect such a spacecraft to undergo high-voltage charging. It should also permit such charging to occur in sunlight. Their results yield a tentative prediction that the Shuttle Orbiter is a large enough spacecraft for such charging, if one adopts the usual definition of high-voltage charging as involving surface potentials at least 100 V different from space potential. The mechanism involves the suppression of electron emission by a potential barrier in the spacecraft wake. In contrast with barrier effects charging in geosynchronous orbit conditions, (1) this barrier is produced by unbalanced electron space charge and not by the presence of surfaces at larger negative potentials elsewhere on the spacecraft, (2) instead of limiting differential charging, this barrier produced it, and (3) instead of a saddle point, the potential distribution involves a minimum which migrates toward the spacecraft and almost reaches it as the spacecraft charges toward a steady state. They also apply this mechanism to propose an explanation for features of Shuttle Orbiter charging observed during the SEPAC (Space Experiments With Particle Accelerators) Spacelab 1 electron beam experiment

[en] The 'ponderomotive-force' effect causes strong repulsion of electrons from the region close to an intensely driven antenna in a space plasma. Under certain conditions, the resulting disturbed sheath around the antenna includes a region which has the essential properties of a double layer, but differs in various ways from the more usual types of double layer. (Auth.)

[en] A theoretical treatment is given for the double-probe method in an electron/positive-ion plasma having mean free path << probe size << Debye length, i.e. under conditions in which neither collisionless theories nor continuum theories of previous workers are applicable. The theory applies to any probe geometry, including spheres and finite cylinders. Applications to plasma diagnostics are developed in detail. (author)

[en] A theory is presented for a spherical electrostatic probe in a collisionless, Maxwellian plasma containing a uniform magnetic field. The theory yields two upper bounds and an adiabatic limit for collection of the attracted particle species (either electrons or ions). For the repelled species, it yields a lower and an upper bound. The theory is similar in concept to existing theories for cylindrical probes by Laframboise and Rubinstein. It is applicable when the ratio of probe radius to Debye length is small enough, and/or the probe potential is large enough, that no potential barriers exist near the probe. Otherwise, a theory of Sanmartin applies. The attracted-particle current in the adiabatic limit, i.e., when mean gyroradius<< Debye length, shows negative-resistance behavior. One of the upper bounds is based on the use of particle canonical angular momentum conservation to define allowed and forbidden regions for particle orbits, and generalizes an existing theory by Parker and Murphy to include particle thermal motion

[en] A flat-ended variant of a multi-electrode electrostatic plasma probe design, previously proposed by Laframboise and Parker, is described. The probe consists of a collector, a guard, and a sleeve electrode. Besides being easier to construct, this modified probe geometry is more amenable to numerical verification of its operating properties. Such a verification is carried out by numerically following selected collisionless orbits of charged particles in the electric field of the probe. By the same means, an orbit-limited operating regime of electrode bias combinations is also found. It is found that if the sleeve is given an attractive bias at least three times as large as that of the collector and guard, relative to space potential, then one achieves the intended probe operation, which simulates that of an orbit-limited spherical Langmuir probe in collisionless conditions but with certain restrictions on probe operation removed or relaxed. It is concluded that experimental tests of the proposed probe configuration are desirable