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Results for “Electrostatic accelerators”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Nano-Newton Electrostatic Force Actuators for Femto-Newton-Sensitive Measurements: System Performance Test in the LISA Pathfinder Mission

Electrostatic force actuation is a key component of the system of geodesic reference test masses (TM) for the LISA orbiting gravitational wave observatory and in particular for performance at low frequencies, below 1 mHz, where the observatory sensitivity is limited by stray force noise. The system needs to apply forces of order 10 −9 N while limiting fluctuations in the measurement band to levels approaching 10 −15 N=Hz 1/2 . We present here the LISA actuation system design, based on audio-frequency voltage carrier signals, and results of its in-flight performance test with the LISA Pathfinder test mission. In LISA, TM force actuation is used to align the otherwise free-falling TM to the spacecraft-mounted optical metrology system, without any forcing along the critical gravitational wave-sensitive interferometry axes. In LISA Pathfinder, on the other hand, the actuation was used also to stabilize the TM along the critical x axis joining the two TM, with the commanded actuation force entering directly into the mission’s main differential acceleration science observable. The mission allowed demonstration of the full compatibility of the electrostatic actuation system with the LISA observatory requirements, including dedicated measurement campaigns to amplify, isolate, and quantify the two main force noise contributions from the actuation system, from actuator gain noise and from low frequency “in band” voltage fluctuations. These campaigns have shown actuation force noise to be a relevant, but not dominant, noise source in LISA Pathfinder and have allowed performance projections for the conditions expected in the LISA mission.

M. Armanos↗
NASA NTRS1986

Plasma processes driven by current sheets and their relevance to the auroral plasma

Plasma processes dealing with ac and dc electric fields, the formation of ion beams and conics, and electron acceleration are considered, and similarities between simulation results and satellite-based observations are discussed. Electrostatic shock-type electric fields are found to occur near the current sheet edges, and double layers having upward electric fields form inside the sheet and are distinguishable from the large perpendicular electric fields only in wide sheets with thicknesses much greater than the ion Larmor radius. It is found that the most energetic ions have pitch angles near 90 deg, indicating a large perpendicular acceleration of the ions, and that the downward accelerating electrons inside the sheet are neither monoenergetic nor perfectly field aligned.

Singh, Nagendra↗
NASA NTRS1988

Particle acceleration and wave emissions associated with the formation of auroral cavities and enhancements

A unified model is presented which interrelates the various processes involved in auroral particle acceleration and the associated wave emissions, and it is shown how energy is coupled from the magnetosphere into the ionosphere. The phenomena in the magnetotail which can provide the source of free energy for the perpendicular electrostatic shocks are identified along with the associated potential structures in the nightside auroral region. The characteristics of the particle acceleration produced by the shock are described, including efficiency and energy transport between magnetospheric and ionospheric plasmas, the properties of the particle distributions throughout the shock region and return current regions, and the associated wave emissions. The source of free energy for the generation of ion conics is identified, as are the signatures for the formation of plasma cavities and/or enhancements.

Winglee, R. M.↗
NASA NTRS1986

Numerical simulations of auroral plasma processes. I - Ion beams and conics. II - Electric fields

The characteristics of ion beams and conics as seen in two-dimensional numerical simulations in which the plasmas are driven by current sheets of a finite thickness are described. It is shown that the most energetic ions in the simulations have pitch angles near 90 deg, implying a large perpendicular acceleration of the ions. Large perpendicular electric fields, similar to those measured in electrostatic shocks, are mainly confined near the edges of the current sheets, where E-perpendicular is much larger than E-parallel. Double layers with E-perpendicular about equal to, and spatially separated from, E-parallel form in the interior of wide current sheets. Such double layers have upward electric fields in the region of the upward current. Downward electric fields develop outside the current sheet.

Singh, Nagendra↗
NASA NTRS1993

Ion acceleration and abundance enhancements by electron beam instabilities in impulsive solar flares

We show that a nonrelativistic electron beam in a hydrogen-helium solar flare plasma will excite H(+) electromagnetic ion cyclotron, shear Alfven, and R-X waves, in addition to waves resulting from the two-stream instability. The H(+) electromagnetic ion cyclotron and shear Alfven waves are able to selectively accelerate ambient He-3 and Fe, respectively, to MeV energies through first harmonic gyroresonance, and thereby account for the large (He-3)/(He-4) and Fe/C ratios seen in the energetic particles from impulsive solar flares. In this model, separate heating and acceleration mechanisms for either He-3 or Fe are not required, and Fe acceleration is quite efficient since it does not need to occur by second harmonic gyroresonance. The combination of the other two unstable modes is able to accelerate ions to hundreds of MeV if the particles become trapped in an electrostatic potential well of a two-stream wave.

Miller, James A.↗
NASA NTRS2015

NASA Innovative Advanced Concepts (NIAC): Heliopause Electrostatic Rapid Transit System (HERTS), Final Report

This report represents a summary of the study conducted under NASA Innovative Concept study contract number 14-NIAC14B-0075. The report provides a summary of the results of all contracted tasks and provides a suggested roadmap for continued development. The effort was collaborated with the Finnish Metrological Institute on an unfunded basis and the results of that coordination are reported herein. The Heliopause Electrostatic Rapid Transit System (HERTS) provides a flexible and enabling technology that can accelerate a spacecraft to velocities that allow travel times on the order of a decade for reaching the Heliopause; a feat that took the Voyager spacecraft(s) over 30 years to perform. The propulsion system concept being described is faster than any current propulsion system underdevelopment by NASA. The report describes the mission, the propulsion concept, and solar system trajectories. It also provides a comparison to the current state of the art in advanced propulsion concepts.

Travel↗
NASA NTRS1990

Plasma particle simulation of electrostatic ion thrusters

Charge exchange collisons between beam ions and neutral propellant gas can result in erosion of the accelerator grid surfaces of an ion engine. A particle in cell (PIC) is developed along with a Monte Carlo method to simulate the ion dynamics and charge exchange processes in the grid region of an ion thruster. The simulation is two-dimensional axisymmetric and uses three velocity components (2d3v) to investigate the influence of charge exchange collisions on the ion sputtering of the accelerator grid surfaces. An example calculation has been performed for an ion thruster operated on xenon propellant. The simulation shows that the greatest sputtering occurs on the downstream surface of the grid, but some sputtering can also occur on the upstream surface as well as on the interior of the grid aperture.

Peng, Xiaohang↗
NASA NTRSDate not supplied

Bessel Tube to Capture Lunar Volatiles

Current arts to create linear motion or acceleration of fine particles and molecules into devices such as mass spectrometers and vacuum pumps rely on the pressure difference created by a pinhole or mechanical processes. However, in an environment of vacuum, these approaches do not create such a pressure differential to drive and move fine particles and molecules. In some cases, electrostatic or magnetic processes may work to create the desired motion. A cylindrical harmonic of electric field, which is widely used in electron accelerators, offers a unique capability to capture and induce a linear motion of molecules and particles when electrically charged. Generally, lunar volatiles are electrostatically charged. The idea to capture and collect the lunar volatiles by creating a drift axis of motion using a cylindrical harmonic field has led to the development of a device concept, called a Bessel Tube. The Bessel Tube concept ingests fine particles, gaseous atoms, and gaseous molecules and guides them along an extraction tube for collection, separation, and analysis. The Bessel Tube concept for lunar volatile collection is discussed.

Bessel Tube↗
NASA NTRS1996

Impingement-Current-Erosion Characteristics of Accelerator Grids on Two-Grid Ion Thrusters

Accelerator grid sputter erosion resulting from charge-exchange-ion impingement is considered to be a primary cause of failure for electrostatic ion thrusters. An experimental method was developed and implemented to measure erosion characteristics of ion-thruster accel-grids for two-grid systems as a function of beam current, accel-grid potential, and facility background pressure. Intricate accelerator grid erosion patterns, that are typically produced in a short time (a few hours), are shown. Accelerator grid volumetric and depth-erosion rates are calculated from these erosion patterns and reported for each of the parameters investigated. A simple theoretical volumetric erosion model yields results that are compared to experimental findings. Results from the model and experiments agree to within 10%, thereby verifying the testing technique. In general, the local distribution of erosion is concentrated in pits between three adjacent holes and trenches that join pits. The shapes of the pits and trenches are shown to be dependent upon operating conditions. Increases in beam current and the accel-grid voltage magnitude lead to deeper pits and trenches. Competing effects cause complex changes in depth-erosion rates as background pressure is increased. Shape factors that describe pits and trenches (i.e. ratio of the average erosion width to the maximum possible width) are also affected in relatively complex ways by changes in beam current, ac tel-grid voltage magnitude, and background pressure. In all cases, however, gross volumetric erosion rates agree with theoretical predictions.

Barker, Timothy↗
NASA NTRS1988

Current driven instabilities of an electromagnetically accelerated plasma

A plasma instability that strongly influences the efficiency and lifetime of electromagnetic plasma accelerators was quantitatively measured. Experimental measurements of dispersion relations (wave phase velocities), spatial growth rates, and stability boundaries are reported. The measured critical wave parameters are in excellent agreement with theoretical instability boundary predictions. The instability is current driven and affects a wide spectrum of longitudinal (electrostatic) oscillations. Current driven instabilities, which are intrinsic to the high-current-carrying magnetized plasma of the magnetoplasmadynmic (MPD) accelerator, were investigated with a kinetic theoretical model based on first principles. Analytical limits of the appropriate dispersion relation yield unstable ion acoustic waves for T(i)/T(e) much less than 1 and electron acoustic waves for T(i)/T(e) much greater than 1. The resulting set of nonlinear equations for the case of T(i)/T(e) = 1, of most interest to the MPD thruster Plasma Wave Experiment, was numerically solved to yield a multiparameter set of stability boundaries. Under certain conditions, marginally stable waves traveling almost perpendicular to the magnetic field would travel at a velocity equal to that of the electron current. Such waves were termed current waves. Unstable current waves near the upper stability boundary were observed experimentally and are in accordance with theoretical predictions. This provides unambiguous proof of the existence of such instabilites in electromagnetic plasma accelerators.

Chouetri, E. Y.↗
NASA NTRS1985

Electromagnetic electron beam instabilities - Hot, isotropic beams

This paper considers the linear theory of electromagnetic instabilities driven by an electron beam in a homogeneous, nonrelativistic, Vlasov plasma. The beam is relatively hot, isotropic in its own frame, and streams parallel or antiparallel to a magnetic field B. Numerical solutions of the full dispersion equation for propagation parallel or antiparallel to B are presented, and the linear properties of the whistler heat flux and electron beam firehose instabilities are exhibited and compared. Under a broad range of parmameters the former mode has the lower beam speed threshold, and the larger maximum growth rate. In addition, it is demonstrated that, for a sufficiently large relative beam density, relative beam temperature, and plasma beta the whistler heat flux instability has a much lower beam speed threshold than the electrostatic electron beam instability. The application of these instabilities to first-order Fermi acceleration of electrons at space plasma shocks is discussed.

Gary, S. P.↗
NASA NTRS1987

GRADIO three-axis electrostatic accelerometers

Dedicated accelerometers for satellite gravity gradiometry (GRADIO project) are described. The design profits from experience acquired with the CACTUS accelerometer payload of the satellite CASTOR-D5B and studies of highly accurate accelerometers for inertial navigation. The principle of operation, based on a three-axis electrostatic suspension of a cubic proof mass, is well suited for the measurements of accelerations less than 0.0001 m/sec/sec. A resolution better than 10 to the minus 11th power m/sec/sec/sq root Hz is expected.

Bernard, A.↗
NASA NTRS2011

First Results from ARTEMIS, a New Two-Spacecraft Lunar Mission: Counter-Streaming Plasma Populations in the Lunar Wake

We present observations from the first passage through the lunar plasma wake by one of two spacecraft comprising ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun), a new lunar mission that re-tasks two of five probes from the THEMIS magnetospheric mission. On Feb 13, 2010, ARTEMIS probe P1 passed through the wake at 3.5 lunar radii downstream from the Moon, in a region between those explored by Wind and the Lunar Prospector, Kaguya, Chandrayaan, and Chang'E missions. ARTEMIS observed interpenetrating proton, alpha particle, and electron populations refilling the wake along magnetic field lines from both flanks. The characteristics of these distributions match expectations from self-similar models of plasma expansion into vacuum, with an asymmetric character likely driven by a combination of a tilted interplanetary magnetic field and an anisotropic incident solar wind electron population. On this flyby, ARTEMIS provided unprecedented measurements of the interpenetrating beams of both electrons and ions naturally produced by the filtration and acceleration effects of electric fields set up during the refilling process. ARTEMIS also measured electrostatic oscillations closely correlated with counter-streaming electron beams in the wake, as previously hypothesized but never before directly measured. These observations demonstrate the capability of the comprehensively instrumented ARTEMIS spacecraft and the potential for new lunar science from this unique two spacecraft constellation.

Halekas, J. S.↗
NASA NTRS2014

First Results from ARTEMIS, A New Two-Spacecraft Lunar Mission: Counter-Streaming Plasma Populations in the Lunar Wake

We present observations from the first passage through the lunar plasma wake by one of two spacecraft comprising ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun), a new lunar mission that re-tasks two of five probes from the THEMIS magnetospheric mission. On Feb 13, 2010, ARTEMIS probe P1 passed through the wake at approximately 3.5 lunar radii downstream from the Moon, in a region between those explored by Wind and the Lunar Prospector, Kaguya, Chandrayaan, and Chang'E missions. ARTEMIS observed interpenetrating proton, alpha particle, and electron populations refilling the wake along magnetic field lines from both flanks. The characteristics of these distributions match expectations from self-similar models of plasma expansion into vacuum, with an asymmetric character likely driven by a combination of a tilted interplanetary magnetic field and an anisotropic incident solar wind electron population. On this flyby, ARTEMIS provided unprecedented measurements of the interpenetrating beams of both electrons and ions naturally produced by the filtration and acceleration effects of electric fields set up during the refilling process. ARTEMIS also measured electrostatic oscillations closely correlated with counter-streaming electron beams in the wake, as previously hypothesized but never before directly measured. These observations demonstrate the capability of the comprehensively instrumented ARTEMIS spacecraft and the potential for new lunar science from this unique two spacecraft constellation.

Plasma↗
NASA NTRS1990

Electron beam injection during active experiments. I - Electromagnetic wave emissions

The wave emissions produced in Echo 7 experiment by active injections of electron beams were investigated to determine the properties of the electromagnetic and electrostatic fields for both the field-aligned and cross-field injection in such experiments and to evaluate the sources of free energy and relative efficiencies for the generation of the VLF and HF emissions. It is shown that, for typical beam energies in active experiments, electromagnetic effects do not substantially change the bulk properties of the beam, spacecraft charging, and plasma particle acceleration. Through simulations, beam-generated whistlers; fundamental z-mode and harmonic x-mode radiation; and electrostatic electron-cyclotron, upper-hybrid, Langmuir, and lower-hybrid waves were identified. The characteristics of the observed wave spectra were found to be sensitive to both the ratio of the electron plasma frequency to the cyclotron frequency and the angle of injection relative to the magnetic field.

Winglee, R. M.↗
NASA NTRS1980

Electron energy distributions measured during electron beam/plasma interactions

In the large vacuum facility at the NASA-Johnson Space Center an electron beam was projected 20 m parallel to B from a gun with variable accelerating potential (1.0 to 2.5 kV) to an aluminum target. The ionospheric neutral pressure and field were approximated. Beam electron energy distributions were measured directly using an electrostatic deflection analyzer and indirectly with a detector that responded to the X-rays produced by electron impact on the target. At low currents the distribution is sharply peaked at the acceleration potential. At high currents a beam plasma discharge occurs and electrons are redistributed in energy so that the former energy peak broadens to 10-15 percent FWHM with a strongly enhanced low energy tail. At the 10% of maximum point the energy spectrum ranges from less than 1/2 to 1.2 times the gun energy. The effect is qualitatively the same at all pitch angles and locations sampled.

Jost, R. J.↗
NASA NTRS1972

Duration test of an annular colloid thruster.

An annular colloid thruster was continuously operated for 1023 hours. Performance was stable with no sparking and negligible drain currents observed. An average thrust of 25.1 micropounds and an average specific impulse of 1160 seconds were obtained at an accelerating voltage of 15 k he thruster exhaust beam was continuously neutralized using electrons and electrostatic vectoring was demonstrated periodically. The only clear trend with time was an increase in specific impulse during the last third of the test period. From these results the thruster lifetime was estimated to be over an order of magnitude greater than the test duration.

Perel, J.↗
NASA NTRS1997

Photoelectron Effects on the Self-Consistent Potential in the Collisionless Polar Wind

The presence of unthermalized photoelectrons in the sunlit polar cap leads to an enhanced ambipolar potential drop and enhanced upward ion acceleration. Observations in the topside ionosphere have led to the conclusion that large-scale electrostatic potential drops exist above the spacecraft along polar magnetic field lines connected to regions of photoelectron production. A kinetic approach is used for the O(+), H(+), and photoelectron (p) distributions, while a fluid approach is used to describe the thermal electrons (e) and self-consistent electric field (E(sub II)) electrons are allowed to carry a flux that compensates for photoelectron escape, a critical assumption. Collisional processes are excluded, leading to easier escape of polar wind particles and therefore to the formation of the largest potential drop consistent with this general approach. We compute the steady state electric field enhancement and net potential drop expected in the polar wind due to the presence of photoelectrons as a function of the fractional photoelectron content and the thermal plasma characteristics. For a set of low-altitude boundary conditions typical of the polar wind ionosphere, including 0.1% photoelectron content, we found a potential drop from 500 km to 5 R(sub E) of 6.5 V and a maximum thermal electron temperature of 8800 K. The reasonable agreement of our results with the observed polar wind suggests that the assumptions of this approach are valid.

Khazanov, G. V.↗