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At least 343 records · Page 19

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NASA NTRS1981

Synchrotron cooling and annihilation of an e/+/-e/-/ plasma - The radiation mechanism for the 5 March, 1979 transient

Positron-electron pair radiation is examined as a mechanism that could be responsible for the impulsive phase emission of the 5 March, 1979 transient. Synchrotron cooling and subsequent annihilation of the pairs can account for the energy spectrum, the very high brightness, and the 0.4 MeV feature observed from this transient, whose source is likely to be a neutron star in the supernova remnant N49 in the Large Magellanic Cloud. In this model, the observed radiation is produced in the skin layer of a hot, radiation-dominated pair atmosphere, probably confined to the vicinity of the neutron star by a strong magnetic field. In this layer, about 10 to the 12th generations of pairs are formed (by photon-photon collisions), cooled and annihilated during the 0.15 s duration of the impulsive phase.

Ramaty, R.↗

NASA NTRS1989

The influence of centrifugal forces on the B field structure of an axially symmetric equilibrium magnetosphere

A model is presented of an axially symmetric pole-on magnetosphere in MHD force balance, in which both plasma thermal pressure gradients and centrifugal force are taken into account. Assuming that planetary rotation leads to differentially rotating magnetotail field lines, the deformation of magnetotail field lines under the influence of both thermal plasma pressure and centrifugal forces was calculated. Analytic solutions to the Grad-Shafranov equation are presented, which include the centrifugal force term. It is shown that the nonrotational magnetosphere with hot thermal plasma leads to a field configuration without a toroidal B(phi) component and without field-aligned Birkeland currents. The other extreme, a rapidly rotating magnetosphere with cold plasma, leads to a configuration in which plasma must be confined within a thin disk in a plane where the radial magnetic field component B(r) vanishes locally.

Ye, Gang↗

NASA NTRS1992

High resolution observations of the magnetic and velocity field of simple sunspots

We have observed the disk passage of relatively simple round sunspots using a narrowband filter and a large format CCD detector and have created magnetograms, Dopplergrams, and continuum images nearly simultaneously. In addition the spectral resolution of the filter allows the construction of 'spectra' for all points in the field of view. The mean inclination of the magnetic field increases from 45-50 deg to 70-75 deg across the penumbra and there is a fluctuation of the inclination angle about the mean of about 4 +/- 18 deg. The variation in inclination is large enough that substantial amounts of magnetic field are parallel to the solar surface from the mid to outer penumbra. The Evershed flow tends to occur in the regions where the magnetic field is horizontal. This suggests that the Evershed flow is confined to the regions of horizontal fields. We show that a simple sunspot model with azimuthal variations in inclination but no azimuthal variations of field strength is free from azimuthal Lorentz forces. The meridional component of the currents which arise from the azimuthal variation in inclination are parallel to the field lines. This suggests that a cylindrically symmetric magnetostatic sunspot model can be perturbed into one with azimuthal variations in inclination with some adjustment in the meridional force balance.

Title, Alan M.↗

NASA NTRS1972

A study of the methods for the production and confinement of high energy plasmas

The injection of dense plasmas into a B sub z long magnetic field from both ends of the field coil was investigated. Deflagration plasma guns and continuous flow Z-pinch are discussed along with the possibility of a continuous flow Z-pinch fusion reactor. The injection experiments are described with emphasis on the synchronization of the two plasma deflagration guns, the collision of the two plasma beams, and the determination of plasma density.

Cheng, D. Y.↗

NASA NTRS2002

Observations of Confinement of a Paramagnetic Liquid in Model Propellant Tanks in Microgravity by the Kelvin Force

The magnetic Kelvin force has been proposed as an artificial gravity to control the orientation of paramagnetic liquid propellants such as liquid oxygen in a microgravity environment. This paper reports experiments performed in the NASA "Weightless Wonder" KC-135 aircraft, through the Reduced Gravity Student Flight Opportunities Program. The aircraft flies through a series of parabolic arcs providing about 25 s of microgravity in each arc. The experiment was conceived, designed, constructed, and performed by the undergraduate student team and their two faculty advisors. Two types of tanks were tested: square-base prismatic tanks 5 cm x 5 cm x 8.6 cm and circular cylinders 5 cm in diameter and 8.6 cm tall. The paramagnetic liquid was a 3.3 molar solution of MnCl2 in water. Tests were performed with each type of tank filled to depths of 1 cm and 4 cm. Each test compared a pair of tanks that were identical except that the base of one was a pole face of a 0.6 Tesla permanent magnet. The Kelvin force attracts paramagnetic materials toward regions of higher magnetic field. It was hypothesized that the Kelvin force would hold the liquid in the bottom of the tanks during the periods of microgravity. The tanks were installed in a housing that could slide on rails transverse to the flight direction. By manually shoving the housing, an identical impulse could be provided to each tank at the beginning of each period of microgravity. The resulting fluid motions were videotaped for later analysis.

Kuhlman, John↗

NASA NTRS1978

Helium /3/ rich solar flares

Several aspects of a solar flare model that emphasizes evidence for the formation of current filaments as mechanisms of field dissipation are discussed. The origin of flare magnetic fields is considered, along with the thermal distribution, electron density, and high-energy X ray emission of flares. It is suggested that the extreme He-3 enrichment in some solar flares is due to spallation and the subsequent confinement of spallation products in a high-temperature high-density plasma associated with the magnetic instability that produces the flare. A current filament is assumed to produce the spallation and maintain the temperature that yields the high-energy X-ray spectrum and depletes the isotopes D, Li, Be, and B, as observed.

Colgate, S. A.↗

NASA NTRS2015

Magnetotail dynamics at Mars: Initial MAVEN observations

We report on the complex nature of the induced Martian magnetotail using simultaneous magnetic field and plasma measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Two case studies are analyzed from which we identify (1) repetitive loading and unloading of tail magnetic flux as the field magnitude changes dramatically, exhibiting signatures similar to substorm activity within intrinsic magnetospheres; (2) multiple current sheet crossings indicative of plasma sheet flapping; (3) tailward flowing high-energy planetary ions (O+ and O2+), confined exclusively to the cross-tail current sheet, contributing to atmospheric escape; and (4) signatures of magnetic flux ropes, suggesting the occurrence of tail reconnection. These events illustrate the complexity of the Martian magnetotail as MAVEN provides key observations relevant to the unanswered questions of induced magnetosphere dynamics.

Gina A Dibraccio↗

NASA NTRS1978

Cosmic electrons, galactic radio background and cosmic ray confinement

Cosmic ray electron measurements and radio background data are analyzed to obtain bounds on the galactic magnetic fields. It is shown that the magnetic field required to explain the radio flux must be greater than 2 micro Gauss. The difference in the steepening of the radio spectra towards the Anticenter and the Halo Minimum provides evidence that the magnetic field decreases with the height above the galactic plane. The calculations of Bulanov and Dogiel (1975) are applied to the radio and electron observations. It is shown that the most plausible interpretation of these results requires that the electron injection spectrum has an intrinsic flattening below a few GeV. The observed steepening of radio and electron data is apparently a combined effect of the injection spectrum and the first break due to continuous energy loss of electrons in space.

Badhwar, G. D.↗

NASA NTRS1980

A study of the Jovian forbidden line S II nebula at high spectral resolution

Observations of forbidden line S II 6716-6731 A emissions from the Jovian magnetosphere have been carried out with a PEPSIOS spectrometer at the Hale 5 m telescope. Spectral resolving power was sufficient to resolve the forbidden line S II line widths. From measured 6716-6731 A doublet ratios and spectral line widths a thermal plasma is found characterized by temperatures about 2 x 10 to the 4th K and electron densities about 2000 cu cm. The source of forbidden line S II emissions was centered within a toroidal region of radius 5 Jupiter radii (inside the orbit of Io), with tight latitudinal confinement near the equilibrium equator for ions in the tilted corotating Jovian magnetic field, and significant long-lived longitudinal structure.

Trauger, J. T.↗

NASA NTRS1995

Mirroring of fast solar flare electrons on a downstream corotating interaction region

We discuss an example of confinement of fast solar electrons by a discrete solar wind-interplanetary magnetic field structure on February 22, 1991. The structure is about 190,000 km in width and is clearly defined by changes in the direction of the magnetic field at the Ulysses spacecraft. This structure carries electrons moving toward the Sun as well as away from the Sun. A loss cone in the angular distribution of the fast electrons shows that mirroring, presumably magnetic, takes place downstream from the spacecraft. Following passage of this narrow structure, the return flux vanishes for 21 min after which time the mirroring resumes and persists for several hours. We identify the enhanced magnetic field region lying downstream from the Ulysses spacecraft that is responsible for the mirroring to be a corotating stream interaction region. Backstreaming suprathermal electron measurements by the Los Alamos National Laboratory plasma experiment on the Ulysses spacecraft support this interpretation.

Anderson, K. A.↗

NASA NTRS2005

Frontiers of Life Sciences: The Human Exploration of the Moon and Mars

The rapid development of the productive processes after World War II extended human settlements into new ecological niches. Advances in Life Sciences played a decisive role supporting the establishment of human presence in areas of the planet where human life could have not existed otherwise. The evolution of life support systems, and the fabrication of new materials and technologies has enabled humans to inhabit Polar Regions, ocean surfaces and depths; and to leave Earth and occupy Low Earth Orbit. By the end of the 20 th Century, stations in the Antarctic and Arctic, off shore oil platforms, submarines, and space stations had become the ultimate demonstration of human ability to engineer habitats at Earth extreme environments and outer space. As we enter the 21st Century, the next development of human settlements will occur through the exploration of the Moon, Mars, and beyond. The major risks of space exploration derive from long exposure of humans and other life systems to radiation, microgravity, isolation and confinement, dependence on artificial life support systems, and unknown effects (e.g., altered magnetic fields, ultrahigh vacuum on bacteria, fungi, etc.). Countermeasures will require a complete characterization of human and other biological systems adaptation processes. To sustain life in transit and on the surface of the Moon and Mars will require a balance of spacecraft, cargo, astronaut crews, and the use of in situ resources. Limitations on the number of crewmembers, payloads, and the barrenness of the terrain require a novel design for the capabilities needed in transit and at exploration outpost sites. The planned destinations have resources that may be accessed to produce materials, food, shelter, power, and to provide an environment compatible with successful occupation of longterm exploration sites. Once more, the advancements of Life Sciences will be essential for the design of interplanetary voyages and planetary surface operations. This presentation delineates the role of Life Sciences and its frontiers, especially Cell Science, in the context of human exploration. Life support systems, food production, and medical equipment encompass many of vital aspects related to the new vision for NASA.

North, Regina M.↗

NASA NTRS1981

Magnetically induced cylindrical stress waves in a thermoelastic conductor

The problem of stress wave generation in a linear thermoelastic solid by a pulsed magnetic field is investigated both analytically and experimentally for a cylindrically symmetric conducting solid. A dynamic response analysis is developed to correlate magnetic, thermal, and stress fields in the solid with the time history of the electric current. In the experiment, a transient magnetic field was applied normal to a large conducting plate with a circular hole. Initially the field was confined to the interior of the circular hole. The field was generated by discharging a large capacitor bank through a solenoidal coil. The plane-stress cylindrical stress waves are 1-D in nature. The relative effects of the magnetic body force and thermoelastic stresses, both generated by the electromagnetic field, are assessed.

Chian, C. T.↗

NASA NTRS1995

The role of photospheric magnetic fields in the variation of solar oscillation eigenfrequencies

The frequencies of solar oscillations have been found to be higher at the peak of the solar cycle, their variation being consistent with that expected from a change in the solar structure confined to the Sun's outer layers. In this work, a technique is introduced for estimating the effect of the highly inhomogeneous photospheric magnetic field on solar oscillation eigenfrequencies, and its results are compared with the solar data. It is found that the observed steep rise in frequency shift at low frequency and the leveling of or decline at high frequency are well reproduced by the model. The correct order of magnitude for the frequency changes is also reproduced, at least at low frequency. The model implies a particular functional form for the variation of the frequency changes with order and degree, and it is suggested that future advances in observation and theory will therefore allow this model to be confirmed or refuted.

Rosenthal, C. S.↗

NASA NTRS1977

A model for particle confinement in a toroidal plasma subject to strong radial electric fields

The approach adopted in the NASA Lewis Bumpy Torus experiment is to confine and heat a toroidal plasma by the simultaneous application of strong dc magnetic fields and electric fields. Strong radial electric fields (about 1 kV/cm) are imposed by biasing the plasma with up to 12 negative electrode rings which surround its minor circumference. The plasma containment is consistent with a balance of two processes: a radial infusion of ions in those sectors not containing electrode rings, resulting from the radially inward electric fields; and ion losses to the electrode rings, each of which acts as a sink and draws ions out the plasma in the manner of a Langmuir probe in the ion saturation regime. The highest density on axis which has been observed so far in this steady-state plasma is 6.2 trillion particles per cu cm, for which the particle containment time is 2.5 msec. The deuterium ion kinetic temperature for these conditions was in the range of 360 to 520 eV.

Roth, J. R.↗

NASA NTRS1981

Discrete breakup arcs and kinetic Alfven waves

Attention is confined to the extremely narrow auroral structures whose characteristic dimensions perpendicular to the magnetic fields are of the order of several hundred meters or even less. The starting point of the model used here is the assumption that discrete breakup arcs are caused by a change in the magnetosphere convection pattern that is localized in space. Particular attention is given to the shear Alfven mode. It is proposed that discrete breakup arcs are a direct manifestation of kinetic interaction between charged particles and an 'mhd' perturbation. It is stressed that the model applies only to narrow structures (thickness of the order of the plasma skin depth) and to short-lived phenomena (time scales shorter than a dispersion time). It is shown that a change of convection pattern in a spatially limited region leads to the emission of a shear-Alfven wave packet which propagates along the magnetic field line with a characteristic velocity.

Goertz, C. K.↗

NASA NTRS1990

The NASA-Lewis program on fusion energy for space power and propulsion, 1958-1978

An historical synopsis is provided of the NASA-Lewis research program on fusion energy for space power and propulsion systems. It was initiated to explore the potential applications of fusion energy to space power and propulsion systems. Some fusion related accomplishments and program areas covered include: basic research on the Electric Field Bumpy Torus (EFBT) magnetoelectric fusion containment concept, including identification of its radial transport mechanism and confinement time scaling; operation of the Pilot Rig mirror machine, the first superconducting magnet facility to be used in plasma physics or fusion research; operation of the Superconducting Bumpy Torus magnet facility, first used to generate a toroidal magnetic field; steady state production of neutrons from DD reactions; studies of the direct conversion of plasma enthalpy to thrust by a direct fusion rocket via propellant addition and magnetic nozzles; power and propulsion system studies, including D(3)He power balance, neutron shielding, and refrigeration requirements; and development of large volume, high field superconducting and cryogenic magnet technology.

Schulze, Norman R.↗

NASA NTRS2001

Gasdynamic Mirror Fusion Propulsion Experiment

Nuclear fusion appears to be the most promising concept for producing extremely high specific impulse rocket engines. One particular fusion concept which seems to be particularly well suited for fusion propulsion applications is the gasdynamic mirror (GDM). This device would operate at much higher plasma densities and with much larger LD ratios than previous mirror machines. Several advantages accrue from such a design. First, the high LA:) ratio minimizes to a large extent certain magnetic curvature effects which lead to plasma instabilities causing a loss of plasma confinement. Second, the high plasma density will result in the plasma behaving much more Re a conventional fluid with a mean free path shorter than the length of the device. This characteristic helps reduce problems associated with "loss cone" microinstabilities. An experimental GDM device is currently being constructed at the NASA Marshall Space Flight Center to provide an initial assessment of the feasibility of this type of propulsion system. Initial experiments are expected to commence in the late fall of 2000.

Emrich, William J., Jr.↗

NASA NTRS2002

Current Status of the Gasdynamic Mirror Fusion Propulsion Experiment

Nuclear fusion appears to be the most promising concept for producing extremely high specific impulse rocket engines. One particular fusion concept which seems to be particularly well suited for fusion propulsion applications is the gasdynamic mirror (GDM). An experimental GDM device has been constructed at the NASA Marshall Space Flight Center to provide an initial assessment of the feasibility of this type of propulsion system. An initial shakedown of the device is currently underway with initial experiments slated to occur in late 2001. This device would operate at much higher plasma densities and with much larger L/D ratios than previous mirror machines. The high L/D ratio minimizes to a large extent certain magnetic curvature effects which lead to plasma instabilities causing a loss of plasma confinement. The high plasma density results in the plasma behaving much more like a conventional fluid with a mean free path shorter than the length of the device. This characteristic helps reduce problems associated with 'loss cone' microinstabilities. The device has been constructed to allow a considerable degree of flexibility in its configuration thus permitting the experiment to grow over time without necessitating a great deal of additional fabrication.

Emrich, William J., Jr.↗