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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

The Influence of Current Density and Magnetic Field Topography in Optimizing the Performance, Divergence, and Plasma Oscillations of High Specific Impulse Hall Thrusters

Recent studies of xenon Hall thrusters have shown peak efficiencies at specific impulses of less than 3000 s. This was a consequence of modern Hall thruster magnetic field topographies, which have been optimized for 300 V discharges. On-going research at the NASA Glenn Research Center is investigating this behavior and methods to enhance thruster performance. To conduct these studies, a laboratory model Hall thruster that uses a pair of trim coils to tailor the magnetic field topography for high specific impulse operation has been developed. The thruster-the NASA-173Mv2 was tested to determine how current density and magnetic field topography affect performance, divergence, and plasma oscillations at voltages up to 1000 V. Test results showed there was a minimum current density and optimum magnetic field topography at which efficiency monotonically increased with voltage. At 1000 V, 10 milligrams per second the total specific impulse was 3390 s and the total efficiency was 60.8%. Plume divergence decreased at 400-1000 V, but increased at 300-400 V as the result of plasma oscillations. The dominant oscillation frequency steadily increased with voltage, from 14.5 kHz at 300 V, to 22 kHz at 1000 V. An additional oscillatory mode in the 80-90 kHz frequency range began to appear above 500 V. The use of trim coils to modify the magnetic field improved performance while decreasing plume divergence and the frequency and magnitude of plasma oscillations.

Hofer, Richard R.↗
DOE OSTI2020

Cryogenic goniometer for measurements in pulsed magnetic fields fabricated via additive manufacturing technique

Complex high-precision mechanical devices can be fabricated using 3-dimensional printing technology with the help of computer-aided design. Using 3D stereolithography, we have constructed a cryogenic goniometer for measurements in pulsed magnetic fields of up to 100 T, at temperatures as low as 0.5 K. We review the properties of several materials tested in developing the goniometer and report on its design and performance. The goniometer allows samples to be rotated in situ to a precision of 0.2 deg, so that the field can be applied at many different angles to the samples’ symmetry directions. Following its success, we establish that 3D printing is now a viable technology for pulsed-field and other cryogenic probes.

3D printing↗
NASA NTRS1993

Solar imaging vector magnetograph

This report describes an instrument which has been constructed at the University of Hawaii to make observations of the magnetic field in solar active regions. Detailed knowledge of active region magnetic structures is crucial to understanding many solar phenomena, because the magnetic field both defines the morphology of structures seen in the solar atmosphere and is the apparent energy source for solar flares. The new vector magnetograph was conceived in response to a perceived discrepancy between the capabilities of X ray imaging telescopes to be operating during the current solar maximum and those of existing magnetographs. There were no space-based magnetographs planned for this period; the existing ground-based instruments variously suffered from lack of sensitivity, poor time resolution, inadequate spatial resolution or unreliable sites. Yet the studies of flares and their relationship to the solar corona planned for the 1991-1994 maximum absolutely required high quality vector magnetic field measurements. By 'vector' measurements we mean that the observation attempts to deduce the complete strength and direction of the field at the measurement site, rather than just the line of sight component as obtained by a traditional longitudinal magnetograph. Knowledge of the vector field permits one to calculate photospheric electric currents, which might play a part in heating the corona, and to calculate energy stored in coronal magnetic fields as the result of such currents. Information about the strength and direction of magnetic fields in the solar atmosphere can be obtained in a number of ways, but quantitative data is best obtained by observing Zeeman-effect polarization in solar spectral lines. The technique requires measuring the complete state of polarization at one or more wavelengths within a magnetically sensitive line of the solar spectrum. This measurement must be done for each independent spatial point for which one wants magnetic field data. All the measurements need to be done in a time short compared to the time scale for changes of the solar features being observed. Were it possible, one would want to record all the needed data simultaneously, since temporal variation of atmospheric seeing degrades both the image and the polarization sensitivity. Since the measurements must span four dimensions, two spatial plus polarization and wavelength, we had some freedom to design the instrument to favor some dimensions over others in terms of simultaneity. Our earlier instrument, the Haleakala Stokes Polarimeter, records a range of wavelengths spanning two spectral lines in each reading, but requires two seconds to determine the polarization state and obtains spatial information only by assembling a long sequence of measurements at single locations on the sun. The new instrument sacrifices spectral detail and accuracy in favor of greatly improved imaging characteristics. The scientific goals for this instrument were to measure surface magnetic fields with enough accuracy to permit calculations of photospheric currents, but with a field of view covering an entire typical active region, high spatial resolution, and a fast enough temporal cadence for detecting flare-associated changes in magnetic structures.

Canfield, Richard C.↗
NASA NTRS2017

3D Realistic Modeling of the Interaction of Quiet-Sun Magnetic Fields with the Chromosphere

High-resolution observations and 3D simulations suggest that a local dynamo operates near the surface and produces ubiquitous small-scale magnetic elements, thus contributing to the magnetic carpet in the photosphere and to the magnetic structure and dynamics of the solar atmosphere. It appears that the traditional mechanisms of chromospheric energy and mass transport by acoustic waves and shocks are likely to play a secondary role; instead, the primary drivers in the energetics and dynamics of the chromosphere and transition region are small-scale, previously unresolved, quiet-Sun magnetic fields. These fields appear as ubiquitous, rapidly changing (on the scale of a few seconds), tiny magnetic loops and magnetized vortex tubes. Questions then arise about their origin and dynamics in the chromosphere, their links to magnetic fields in the photosphere, and their role in the energy storage and exchange between subsurface layers and the chromosphere. In the talk we will present results of 3D radiative MHD simulations obtained with the StellarBox code and discuss the energetics and dynamical interlinks between the subphotospheric layers and low chromosphere, their effects on the structure of the chromosphere, and signatures of the fine-scale magnetic features in high-resolution spectro-polarimetric observations.

Quie-Sun↗
NASA NTRS1991

Compressible magnetic convection - Formulation and two-dimensional models

Details on a formulation and numerical solution of the equations of time-dependent magnetized convection are presented. Results on the transition between weak and strong magnetic fields where the highly nonlinear behavior commences are discussed, and the sensitivity of these results to the value of the magnetic resistivity, which can significantly influence the details of the interactions, is indicated. Consideration is given to the consequences of the findings for modeling stellar and solar magnetic fields.

Fox, Peter A.↗
NASA NTRS1983

HZE particle shielding using confined magnetic fields

The great rigidities characteristic of high energy heavy ion (HZE) particles are judged to preclude near term use of confined magnetic fields of reasonable dimensions and strengths for small spacecraft shielding on long duration manned missions. It is noted that a Mars mission-class shield, although effective against solar protons, would be useless for HZE particles unless the mass and size of the shield are increased by several orders of magnitude (to yield a shield comparable to those contemplated for permanent space stations).

Townsend, L. W.↗
NASA NTRS1976

Field-aligned currents observed by the Ogo 5 and Triad satellites

The Triad (at a height of 800 km) and Ogo 5 (in the high altitude magnetosphere) magnetic field observations have shown the existence of a field-aligned current system consisting of currents flowing in the polar cap boundary layer and those flowing in another layer located equatorward of the former. In the polar cap boundary layer (identified as the high-latitude boundary of the plasma sheet in the nightside magnetosphere), the current flows into the ionosphere on the morning side and away from the ionosphere on the afternoon side. In the lower-latitude layer, the current directions are reversed. The current in the polar cap boundary layer is considered as the primary field-aligned current system.

Sugiura, M.↗
NASA NTRS2003

High-Energy Two-Stage Pulsed Plasma Thruster

A high-energy (28 kJ per pulse) two-stage pulsed plasma thruster (MSFC PPT-1) has been constructed and tested. The motivation of this project is to develop a high power (approximately 500 kW), high specific impulse (approximately 10000 s), highly efficient (greater than 50%) thruster for use as primary propulsion in a high power nuclear electric propulsion system. PPT-1 was designed to overcome four negative characteristics which have detracted from the utility of pulsed plasma thrusters: poor electrical efficiency, poor propellant utilization efficiency, electrode erosion, and reliability issues associated with the use of high speed gas valves and high current switches. Traditional PPTs have been plagued with poor efficiency because they have not been operated in a plasma regime that fully exploits the potential benefits of pulsed plasma acceleration by electromagnetic forces. PPTs have generally been used to accelerate low-density plasmas with long current pulses. Operation of thrusters in this plasma regime allows for the development of certain undesirable particle-kinetic effects, such as Hall effect-induced current sheet canting. PPT-1 was designed to propel a highly collisional, dense plasma that has more fluid-like properties and, hence, is more effectively pushed by a magnetic field. The high-density plasma loading into the second stage of the accelerator is achieved through the use of a dense plasma injector (first stage). The injector produces a thermal plasma, derived from a molten lithium propellant feed system, which is subsequently accelerated by the second stage using mega-amp level currents, which eject the plasma at a speed on the order of 100 kilometers per second. Traditional PPTs also suffer from dynamic efficiency losses associated with snowplow loading of distributed neutral propellant. The twostage scheme used in PPT-I allows the propellant to be loaded in a manner which more closely approximates the optimal slug loading. Lithium propellant was chosen to test whether or not the reduced electrode erosion found in the Lithium Lorentz Force Accelerator (LiLFA) could also be realized in a pulsed plasma thruster. The use of the molten lithium dense plasma injector also eliminates the need for a gas valve and electrical switch; the injector design fulfills both roles, and uses no moving parts to provide, in principle, a highly reliable propellant feed and electrical switching system. Experimental results reported in this paper include: second-stage current traces, high-speed photographic and holographic imaging of the thruster exit plume, and internal mapping of the discharge chamber magnetic field from B-dot probe data. The magnetic field data is used to create a two-dimensional description of the evolution of the current sheet inside the thruster.

Markusic, Tom↗
NASA NTRS2009

High-Altitude High-Latitude Electron-Density and Magnetic-Field Enhancements Observed during Magnetic Storms - Including the Storm of 17 April 2002

In addition to the spectacular remote measurements from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite [Burch, Space Sci. Rev., 2003], the Radio Plasma Imager (RPI) on IMAGE had the capability of making accurate magnetospheric local electron-density and magnetic-field determinations in addition to obtaining remote electron-density profiles [Reinisch et al., GRL, 2001; Benson et al., JGR, 2003]. These determinations were made using interleaved passive and active modes of operation of the RPI; the former were used to produce dynamic spectra and the latter to produce plasmagrams during active sounding. The plasmagrams of particular interest in this investigation were produced during the apogee (8 RE) portion of the IMAGE orbit when the RPI often operated in a high-resolution mode (300 Hz frequency steps) designed for accurate frequency measurements of sounder-stimulated plasma resonances. Here we present examples from 2001 and 2002, when the IMAGE apogee was at high latitudes, of large increase the electron density and magnetic-field intensity (relative to quiet control conditions) during magnetic storms. During the 17 April 2002 storm, the electron density increased by about a factor of 4 and the magnetic-field intensity increased by nearly a factor of 2. During the much larger storm of 31 March 2001, the RPI data presented in Osherovich et al. [2007] indicates that the electron density increased by about a factor of 10.

Benson, Robert F.↗
DOE OSTI2022

Fully Distributed Multi-Material Magnetic Sensing Structures for Multiparameter DAS Applications

This dissertation demonstrates the first of its kind distributed magnetic field sensor based on a fiber optic distributed acoustic sensing (DAS) scheme. Ferromagnetic nickel and Metglas® were dispersed internally within a fiber optic preform and then drawn on an in-house fiber optic draw tower to lengths in the kilometers. Due to the close proximity of the ferromagnetic metals and fiber optic core, the magnetostrictive strain response of the ferromagnetic materials when exposed to a magnetic field would perturbate within the fiber cladding and transfer that strain, internally, to the fiber optic core. Strain resulting from the magnetostrictive effect allows the DAS based sensor to accurately translate strain into readable magnetic field data. Due to the high sensitivity seen in this sensor design, multiparameter sources, acoustic and magnetic fields, were tested and validated and a three dimensional magnetic-field vector sensor was proposed. Numerical analysis of the novel sensor design was first implemented using COMSOL Multiphysics, where inputs such as magnetostrictive element shape, size, distance, and number were first investigated. Upon optimizing system constraints, the sensor design was further modified such that single mode operation was consistent across multiple fiber draws while retaining high strain transfer from the ferromagnetic elements to the fiber optic core. Ferromagnetic material selection was evaluated as a function of the saturation magnetostriction constants and a total of 4 modules were used to fully characterize the complex physics involved in this sensor design. All fabrication and testing were performed in-house using a full scale 3-story fiber draw tower and custom environmental testing stations to imitate naturally occurring events such as magnetic or acoustic point sources. A unique stacking method was used to embed ferromagnetic nickel and Metglas® into a fiber optic preform which when combined with a custom fiber draw process resulted in consistent multi-material fibers drawn to lengths of 1-km. In-house testing facilities included different types of electromagnetic generators, in addition to a soil test bed, and an outdoor test bed which allowed 100 meters of fiber to be tested simultaneously. All tested sensors demonstrated high strain transfer capabilities on the order of 0.01-10 μϵ depending on the materials used, ferromagnetic rod number, and core to metal spacing. Due to the sensitivity of the system the difference between AC and DC was distinct, and directional magnetostriction was studied. Transverse and longitudinal magnetic wave propagation was controlled through a solenoid and rectangular Helmholtz coil, both built in-house. A three-dimensional magnetic field vector sensor was proposed due to the success of the magnetic field sensor, and a design was proposed and initially tested to validate direction as a function of field strength and distance. To summarize, this dissertation explores the first fully distributed magnetic field sensor using DAS based techniques and one of the first multi-material fiber draw processes which can produce consistent single mode fiber up to 1-km. Due to extensive FEA modeling, multiple iterations of the magnetic sensor were fully characterized and an equation describing the relationship between sensor design and strain transfer has been created and validated experimentally. Multi-parameter tests including acoustic and magnetic fields were implemented and an algorithm was developed to separate the mixed signals. Finally, a test was performed to demonstrate the feasibility of sensing magnetic fields directionally. Cumulative results demonstrate a high-quality sensor alternative to current designs which may surpass other magnetic sensors due to innate multi-parameter capabilities, in addition to the inexpensive production cost and extremely long operating lengths.

02 PETROLEUM↗
DOE OSTI2022

White Paper on High Temperature Superconducting Bi-2212 Magnets for Energy Frontier Circular Colliders

As the only high-temperature superconducting (HTS) material available as an isotropic, twisted, multifilamentary round wire, Bi-2212 is very promising for expanding the high-field superconducting accelerator magnet toolbox beyond the round-wire, isotropic Nb-Ti and Nb3Sn conductors used by HEP so far. In this paper, we describe the important roles that Bi-2212 might play for future high energy circular colliders including both high energy proton and muon colliders. We describe its present technology status (conductor development, magnet design concepts, prototype magnet status) and then provide a ten-year plan for >15 T accelerator magnets and >25 T solenoid magnets within an integrated strategy to engage industry and the entire US and international scientific enterprise interested in HTS magnet applications.

43 PARTICLE ACCELERATORS↗
NASA NTRS2023

CME Propagation Through the Heliosphere: Status and Future of Observations and Model Development

The ISWAT (International Space Weather Action Teams) heliosphere clusters H1 and H2 have a focus on interplanetary space and its characteristics, especially on the large-scale co-rotating and transient structures impacting Earth. Solar wind stream interaction regions, generated by the interaction between high-speed solar wind originating in large-scale open coronal magnetic fields and slower solar wind from closed magnetic fields, are regions of compressed plasma and magnetic field followed by high-speed streams that recur at the ~27 day solar rotation period. Short-term reconfigurations of the lower coronal magnetic field generate flare emissions and provide the energy to accelerate enormous amounts of magnetised plasma and particles in the form of coronal mass ejections into interplanetary space. The dynamic interplay between these phenomena changes the configuration of interplanetary space on various temporal and spatial scales which in turn influences the propagation of individual structures. While considerable efforts have been made to model the solar wind, we outline the limitations arising from the rather large uncertainties in parameters inferred from observations that make reliable predictions of the structures impacting Earth difficult. Moreover, the increased complexity of interplanetary space as solar activity rises in cycle 25 is likely to pose a challenge to these models. Combining observational and modeling expertise will extend our knowledge of the relationship between these different phenomena and the underlying physical processes, leading to improved models and scientific understanding and more-reliable space-weather forecasting. The current paper summarizes the efforts and progress achieved in recent years, identifies open questions, and gives an outlook for the next 5–10 years. It acts as basis for updating the existing COSPAR roadmap by Schrijver et al. (2015), as well as providing a useful and practical guide for peer-users and the next generation of space weather scientists.

Space weather↗
NASA NTRS1992

High-energy spectral breaks in gamma-ray bursts

Model fits are presented for 18 gamma-ray burst spectra from 100 keV to 27 MeV made with the BATSE spectroscopy detectors on the Compton Gamma Ray Observatory. Most of the bursts are well fitted as power laws with spectral indices between -1.36 and -2.29; however, five bursts show definite departures from a simple power-law fit at high energies. Three of these bursts are well fitted with broken power-law spectra and break energies of from 400 to 690 keV, such as might arise from photon-photon interactions. If so, then the source compactness and hence distance will be sharply constrained. Two of the bursts have spectra with sharply confined slope changes and are well fitted with broken power-law spectra with break energies of 1.2 and 1.6 MeV at peak, such as might arise from photon-magnetic field interactions. If so, then these spectral breaks provide strong evidence for the existence of high magnetic fields in the burst emission region.

Schaefer, Bradley E.↗
NASA NTRS1994

A statistical survey of the central plasma sheet

We present a statistical analysis of the ion plasma properties and magnetic field of the central plasma sheet at distances from 10 to 23 R(sub E) from the Earth. This study incorporates International Sun-Earth Explorer (ISEE) 1 plasma sheet samples accumulated with the University of Iowa Lepedea plasma analyzer during 1979. Our study of the bulk properties of the ion plasma shows that there is relatively little change as a result of increasing geomagnetic activity. The main macroscopic effect is an increase in plasma temperature. When the transverse profile of the plasma sheet is examined, it is clear that this increase in temperature occurs preferentially at high latitudes. The magnetic field shows an increase in magnitude in the vicinity of the neutral sheet periods of high geomagnetic activity. The radial profiles of the density, temperature, plasma, and magnetic pressures show a gradient in total energy density in the plasma sheet. The convective velocities are systematically directed earthward, and there is a bias toward positive V(sub y) on the duskside of the magnetotail. We infer that particle motion can be attributed to a pressure gradient, combined with steady state convective electric fields. We compute the convective electric fields from our measured bulk velocities, arriving at a pattern similar to that observed at low altitudes. The cross-tail electric field E(sub y) is dominant near the neutral sheet region, but at high latitudes E(sub z) is a major component. Our results suggest that the plasma sheet boundary layer, rather than the central plasma sheet, is a region of diverging electric fields. The picture of the plasma sheet that emerges from our study is that of a stable reservoir of hot plasma in which thermodynamic, rather than dynamic, processes is important.

Huang, C. Y.↗
NASA NTRS1991

UCSD High Energy X-ray Timing Experiment magnetic shield design and test results

Results are reported from an effort to define a passive magnetic field concept for the High Energy X-ray Timing Experiment (HEXTE), in the interest of reducing the detector-gain variations due to 0.5-1.0-sec timescale magnetic field variations. This will allow a sensitivity of the order of 1 percent of the HEXTE background. While aperture modulation and automatic gain control will minimize effects on timescales of tens of seconds and longer, passive magnetic shielding of the photomultiplier tubes will address 1-sec timescale variations due to aperture motions.

Rothschild, Richard E.↗
NASA NTRS1994

Mode properties of low-frequency waves: Kinetic theory versus Hall-MHD

In fluid theory, the ordering of low-frequency modes in a homogeneous plasma is based on the phase velocity, since modes do not intersect each other in dispersion diagrams as a function of wavenumber or other parameters. In linear kinetic theory, modes cross each other. Thus a consistent and useful classification should be based on the physical properties of the modes instead. This paper attempts such a classification by documeting the dispersion and general mode properties of the low-frequency waves (omega much less than (OMEGA(sub ci) OMEGA(sub ce) (exp 1/2)), where OMEGA(sub ci), OMEGA(sub ce) are the cyclotron frequencies of the ions and electrons, respectively) in kinetic theory, and by comparing them to the results of two-fluid theory. Kinetic theory gives a seperate Alfven/ion-cyclotron (A/IC) wave with phase speed Omega/k approximately = v(sub A) cos theta for omega much less than OMEGA(sub ci), where v(sub A) is the Alfven velocity and theta the angle of propagation between wave vector k and background magnetic field B(sub o). For a given wavenumber, the magnetosonic mode is a double-valued solution with a singular point in theta, beta parameter space, where beta is the ratio of thermal pressure to magnetic pressure. It is shown that a branch cut starting at the singular point theta approximately 30 deg, beta approximately 3 and leading to larger beta gives a practical and consitent seperation of this double-valued magnetosonic solution. Selection of this branch cut results in a moderately damped fast/magnetos onic and a heavily damped slow/sound wave. A comprehensive review of the polarization, compressibility and other mode properties is given and shown to be consistent with the selected branch cut. At small wavenumbers, the kinetic mode properties typically start to deviate significantly from their fluid counterparts at beta approximately 0.5. At larger beta, there is no longer a consistent correspondence between the fluid and kinetic modes. Kinetic theory also dictates the use of different mode properties to distinguish between them in observational data. For example, the phase between the density and magnetic field perturbation may become useless at high beta, whereas the direction of the magnetic field perturbations with respect to k and B(sub o) remains a useful characteristic. Two quantities based on this characteristic are suggested and are shown to be useful also to distinguish between the mirror mode and A/IC waves in a plasma with temperature anisotropy.

Krauss-Varban, D.↗
DOE OSTI2022

Observation of quenching-induced magnetic flux trapping using a magnetic field and temperature mapping system

Highly efficient superconducting radio-frequency cavities exhibit low heat loss and are used as components in accelerators and superconducting devices due to their high Q-values. The precise location of magnetic flux trapping in cavities is necessary to identify its effects on the performance of superconducting cavities. In this study, we report a new combined mapping system to measure the temperature and magnetic field on the equator. The proposed system comprehensively maps local magnetic field changes as magnetic flux trapping due to quenching. Our experimental results show that magnetic flux trapping due to quenching increases the local surface resistance of superconducting cavities at 2 K. Thus, the proposed system elucidates the relationship between local flux trapping due to quenching and surface resistance in superconducting cavities and highlights the effect of quenching on the surface resistance. This system can aid in the development of superconducting cavities with higher Q values.

43 PARTICLE ACCELERATORS↗