Edgar A. Bering

Particle and field signatures during pseudobreakup and major expansion onset

The temporal and spatial scales of the onset of two types of substorm events are investigated. These substorms were cases where the expansion onset had precursor localized auroral activation without significant negative bay enhancement, that is, “pseudobreakup”. High-resolution energetic particle and magnetic field data at synchronous orbit are used for the analysis together with auroral and magnetic field data simultaneously taken from ground-based instrumentation. The auroral structure following the pseudobreakup significantly resembled the major expansion aurora, except in its spatial scale. Typical magnetospheric onset signatures such as tail current diversion, dipolarization, and injection were observed associated with some of the pseudobreakups. The major expansion, on the other hand, consisted of a number of rather localized injections and expansions, each of which had timescales of 2-8 min, a comparable timescale to that of pseudobreakups. This study shows that there does not appear to be any phenomenological differences between pseudobreakups and major expansion onsets. The major difference between pseudobreakups and major expansion onsets would be the number of occurrences, as well as the intensity and the scale size of the magnetospheric source.

Ambipolar ion acceleration in an expanding magnetic nozzle

The helicon plasma stage in the Variable Specific Impulse Magnetoplasma Rocket (VASIMR ® ) VX-200i device was used to characterize an axial plasma potential profile within an expanding magnetic nozzle region of the laboratory based device. The ion acceleration mechanism is identified as an ambipolar electric field produced by an electron pressure gradient, resulting in a local axial ion speed of Mach 4 downstream of the magnetic nozzle. A 20 eV argon ion kinetic energy was measured in the helicon source, which had a peak magnetic field strength of 0.17 T. The helicon plasma source was operated with 25 mg s −1 argon propellant and 30 kW of RF power. The maximum measured values of plasma density and electron temperature within the exhaust plume were 1 × 10 20 m −3 and 9 eV, respectively. The measured plasma density is nearly an order of magnitude larger than previously reported steady-state helicon plasma sources. The exhaust plume also exhibits a 95% to 100% ionization fraction. The size scale and spatial location of the plasma potential structure in the expanding magnetic nozzle region appear to follow the size scale and spatial location of the expanding magnetic field. The thickness of the potential structure was found to be 10 4 to 10 5 λDe depending on the local electron temperature in the magnetic nozzle, many orders of magnitude larger than typical laboratory double layer structures. The background plasma density and neutral argon pressure were 10 15 m −3 and 2 × 10 −5 Torr, respectively, in a 150 m 3 vacuum chamber during operation of the helicon plasma source. The agreement between the measured plasma potential and plasma potential that was calculated from an ambipolar ion acceleration analysis over the bulk of the axial distance where the potential drop was located is a strong confirmation of the ambipolar acceleration process. (Some figures in this article are in colour only in the electronic version)

Evidence that the electrostatic ion cyclotron instability is saturated by ion heating

Observations have been made of electric field oscillations near the local ion gyro frequency and of an intense beam of plasma ions at the edge of an auroral arc. The observations are in good agreement with ion heating as the saturation mechanism for electrostatic ion cyclotron waves.

The hundred year hunt for the sprite

The scientific communitys perception of the middle atmosphere above thunderstorms as “uninteresting” changed completely in the last decade. Today, a host of lightning-related Transient Luminous Events (TLEs) have been identified, including sprites, blue jets, elves, sprite halos, and trolls. Others may remain to be discovered. Aside from the intrinsic scientific issues arising from this linkage of tropospheric electrical phenomena with that of middle atmosphere, a number of practical questions emerge. What, if any threats might TLEs pose to aerospace operations above 20 km? Do sprites represent a heretofore undocumented source of middle atmospheric Nox? What role might they play in the global electrical circuit, as well as in the energetics of the upper atmosphere [Bering et al., 1998]? Might these phenomena impact satellite-based global monitoring and surveillance efforts?

Observations of single-pass ion cyclotron heating in a trans-sonic flowing plasma

The VAriable Specific Impulse Magnetoplasma Rocket (VASIMR®) is a high power electric spacecraft propulsion system, capable of Isp/thrust modulation at constant power [F. R. Chang Diaz et al., Proceedings of the 39th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 8–11 Jan. 2001]. The VASIMR® uses a helicon discharge to generate plasma. This plasma is energized by an rf booster stage that uses left hand polarized slow mode waves launched from the high field side of the ion cyclotron resonance. In the experiments reported in this paper, the booster uses 2–4 MHz waves with up to 50 kW of power. This process is similar to the ion cyclotron heating (ICH) in tokamaks, but in the VASIMR® the ions only pass through the resonance region once. The rapid absorption of ion cyclotron waves has been predicted in recent theoretical studies. These theoretical predictions have been supported with several independent measurements in this paper. The single-pass ICH produced a substantial increase in ion velocity. Pi...

VX-200 Magnetoplasma Thruster Performance Results Exceeding Fifty-Percent Thruster Efficiency

IGH-POWER electric propulsion thrusters can reducepropellant mass for heavy-payload orbit-raising missions andcargo missions to the moon and near-Earth asteroids, and they canreduce the trip time of robotic and piloted planetary missions [1–4].TheVariableSpecificImpulseMagnetoplasmaRocket(VASIMR®)VX-200 engine is an electric propulsion system capable ofprocessing power densities on the order of 6MW

The influence of polar-cap convection on the geoelectric field at Vostok, Antarctica

Abstract Vertical geoelectric field measurements at Vostok, Antarctica ( 78.5° S , 107° E ; corrected geomagnetic latitude, 83.4°S) made during 1998 are compared with both Weimer (1996) and IZMEM (1994) model calculations of the solar-wind-induced, polar-cap potential differences with respect to the station. By investigating the correlations between these parameters for individual UT hours, we confirm and extend the diurnal range over which significant correlations have been obtained. Nineteen individual UT hours are significantly correlated with the Weimer model predictions and nine with the IZMEM model predictions. Diurnal variation in the slopes of the linear regressions allows us to comment on each model, demonstrating that Antarctic polar plateau geoelectric field measurements can be used to investigate polar convection. Seasonal variations in the diurnal electric field variations at Vostok are compared with the Carnegie global electric circuit diurnal curves, after allowance is made for the solar-wind-induced, polar-cap potential difference patterns.

Ground‐based instrumentation for measurements of atmospheric conduction current and electric field at the South Pole

We have constructed instruments to measure the atmospheric conduction current and the atmospheric electric field: two fundamental parameters of the global-electric circuit. The instruments were deployed at the Amundsen-Scott South Pole Station in January 1991 and are designed to operate continuously for up to one year without operator intervention. The atmospheric current is measured by a sensor that uses a split-hemispheric conducting shell of 17.8-cm radius, separated by a thin Teflon insulating disk. The detection electronics are inside the sphere. In principle, the atmospheric current flows into one hemisphere, through the electronics where it is measured, and out the other hemisphere. The electric field is measured by a field mill of the rotating dipole type. The electric field sensing elements are two 30-cm-long antennas, driven to rotate in the vertical plane at 1800 rotations per minute. Two arrays of identical instruments have been deployed, separated by 600 m, in order to distinguish between atmospheric electrical signals of local and global origin. The separation distance of the arrays was determined by the climatology of the Antarctic plateau. Sample data from the first days of operation at the South Pole indicate variations in the global circuit over time scales from minutes, to hours, to days.

Theory and operation of the split Langmuir probe

Abstract An instrument, the split Langmuir probe, has been developed to make in situ measurements of current density and plasma bulk flow. The split Langmuir probe consists of two conducting elements that are separated by a thin insulator that shield each other over a 2π solid angle, and that are simultaneously swept from negative to positive potentials with respect to the plasma. By measuring the current to each plate and the difference current between plates, information can be obtained on the plasmas current density, bulk flow, electron temperature, and density. The instrument was successfully test flown from Fort Churchill on 2 August 1968, with results in reasonable agreement with those from another experiment on the same rocket. Sources of error indicated by these results include plate area differences, plate work function differences, input resistor differences, and probe wake effects. The error signal in the difference current data due to plate work function differences rose to a sharp maximum at plasma potential, which served the useful purpose of precisely marking plasma potential. Possible changes in probe geometry, sweep rate, and telemetry designed to reduce these errors are discussed.

The geoelectric field at Vostok, Antarctica: its relation to the interplanetary magnetic field and the cross polar cap potential difference

The vertical geoelectric field measured at Vostok, Antarctica (78.5°S, 107°E, L=75.0) over the 13 month interval May 1979–May 1980 is correlated with the interplanetary magnetic field (IMF) components By and Bz at times when Vostok is connected to the dayside magnetosphere. No significant association with IMF Bx is found. The interaction of the solar wind and the Earth’s magnetic field generally results in anti-sunward plasma flow in the high-latitude, polar ionosphere driven by a dawn-to-dusk, cross polar cap potential difference pattern. Using the IZMEM model to infer the contribution of the cross polar cap potential difference to the potential difference between the ionosphere and the ground at Vostok for the measured IMF conditions, we show that this provides a viable mechanism for the IMF associations found. We demonstrate that the direct association of the geoelectric field with the cross polar cap potential difference is independent of a result (Park, 1976. Solar magnetic sector effects on the vertical atmospheric electric field at Vostok, Antartica. Geophysical Research Letters 3(8), 475–478) showing an ∼15% decrease in the vertical geoelectric field measured at Vostok, 1–3 days after the passage of IMF sector boundaries. Evidence is also presented supporting the Park result, for which a mechanism is yet to be confirmed.