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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Transverse diffusion of electrons in a magnetoplasma

Plasma density and temperature profiles were measured for plasma electrons which were generated by a plasma source and ionization from a 1 kev electron beam. Electron plasma parameters were measured with a cylindrical Langmuir probe which was moved perpendicular to the axis of the beam and field. Electron densities decreased exponentially from the beam center and the decay constant varied with magnetic field in accordance with the Bohm theory of cross field diffusion. This enhanced diffusion effect due to instabilities generated by the electron beam is orders of magnitude larger than that due to particle collisions.

Mcintyre, Bernard↗
NASA NTRS1988

Simulation of ion-cyclotron-like modes in a magnetoplasma with transverse inhomogeneous electric field

The new kinetic ion-cyclotronlike (IC-like) instability driven by a localized electric field perpendicular to the ambient magnetic field is investigated using particle simulation. The existence of the new mode is demonstrated and the mode is distinguished from the well-known Kelvin-Helmholtz branch and the kinetic modification of this branch. The issue of the initial loading of particles in phase space in the simulation is clarified. The simulation results show that the growing ion waves are associated with the small vortices in the linear state, which evolve into a nonlinear stage dominated by large vortices with lower frequencies.

Nishikawa, K.-I.↗
NASA NTRS1989

ECRH of trapped electrons in laboratory magnetoplasmas

Heating of plasma electrons by high power millimeter wave fields at cyclotron harmonic resonance is studied. A mirror field is modeled for the local trapping of electrons. It is shown that superthermal electrons can be generated as the consequence of the ECRH of trapped electrons.

Kuo, S. P.↗
NASA NTRS1990

Current collection in a flowing magnetoplasma

Effects of plasma drift on the current collection by a long conducting cylinder in a magnetized plasma is studied by means of a 2 1/2 dimensional PIC code. It is found that for the drift velocity (V sub 0) perpendicular to the magnetic field (B sub 0), the electron current collected by a positive cylinder is considerably enhanced depending on the drift velocity. The distributions of plasma and the potential structure around the cylinder for several relative orientations between V sub 0 and B are presented along with the comparisons of current with and without the magnetic field. Simulations with the magnetic field in the simulation plane show that the potential structures around the cylinder are two-dimensional double layers with dimension (L) perpendicular to B much smaller than the dimension (L) parallel to B. In fact, L perpendicular is found to be approximately determined by the current limiting radius given by the Parker-Murphy model. However, it is found that the collected currents in the simulations are generally higher than those given by this model.

Singh, Nagendra↗
NASA NTRS1991

Magnetoplasma sheath waves on a conducting tether in the ionosphere with applications to EMI propagation on large space structures

A recent space experiment confirmed sheath-wave propagation of a kilometer-long insulated wire in the ionosphere, oriented parallel to the Earth's magnetic field. This space tether experiment, Oedipus-A, showed a sheath-wave passband up to about 2 MHz and a phase velocity somewhat slower than the velocity of light in a vacuum, and also demonstrated both ease of wave excitation and low attenuation. The evidence suggests that, on any large structure in low Earth orbit, transient or continuous wave electromagnetic interference, once generated, could propagate over the structure via sheath waves, producing unwanted signal levels much higher than in the absence of the ambient plasma medium. Consequently, there is a need for a review of both electromagnetic interference/electromagnetic compatibility standards and ground test procedures as they apply to large structures in low Earth orbit.

Balmain, K. G.↗
NASA NTRS1991

Lower-hybrid turbulence in a nonuniform magnetoplasma

An experimental study of a pressure-gradient-driven instability in a large discharge plasma is presented. When the electron diamagnetic drift exceeds the sound speed, ion-acoustic-like waves are driven unstable. The growth rate maximizes near the lower-hybrid frequency and the waves propagate essentially across B. The sound waves grow to large amplitudes and saturate by wave steepening and refraction away from the destabilizing drift. Magnetic fluctuations result from electron diamagnetic currents and opposing Hall currents associated with the wave density fluctuations. Ions are essentially unmagnetized and slow compared to the magnetized electrons. In spite of the large amplitude waves little acceleration of electrons or ions is observed.

Stenzel, R. L.↗
NASA NTRS2002

Variable Specific Impulse Magnetoplasma Rocket Engine

An engine is disclosed, including a controllable output plasma generator, a controllable heater for selectably raising a temperature of the plasma connected to an outlet of the plasma generator, and a nozzle connected to an outlet of the heater, through which heated plasma is discharged to provide thrust. In one embodiment, the source of plasma is a helicon generator. In one embodiment, the heater is an ion cyclotron resonator. In one embodiment, the nozzle is a radially diverging magnetic field disposed on a discharge side of the heater so that helically travelling particles in the beater exit the heater at high axial velocity. A particular embodiment includes control circuits for selectably directing a portion of radio frequency power from an RF generator to the helicon generator and to the cyclotron resonator so that the thrust output and the specific impulse of the engine can be selectively controlled. A method of propelling a vehicle is also disclosed. The method includes generating a plasma, heating said plasma, and discharging the heated plasma through a nozzle. In one embodiment, the nozzle is a diverging magnetic field. In this embodiment, the heating is performed by applying a radio frequency electro magnetic field to the plasma at the ion cyclotron frequency in an axially polarized DC magnetic field.

Franklin R Chang-Diaz↗
NASA NTRS2003

Study of the Helicon Source Operation in the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) Experiment

During this research period the following models of the VASIMR helicon discharge have been further developed and applied to analyze the on-going VX- 10 ASPL experiment: A) 1D semi-analytical model for a mixed-collisional propellant flow B) OD power and balance model for the whole helicon discharge In this particular research period we have concentrated on the MW-level performance of the VASIMR helicon source. Favorable high-power scaling and reduced ionization costs were obtained, and presented at the VASIMR NASA review in the Fall '02. This Grant is continuation of the previous NAG9-1224 award. The research results are summarized in 14 publications; they were presented as 20+ talks at the major International Conferences and scientific seminars at the leading Academic and Research Institutions. The reported results allowed helicon discharge characterization, understanding of the several experimental observations, and helped to make predictions and propose structural modifications for the advanced VASIMR helicon source operation.

Molvig, Kim↗
NASA NTRS1972

Wave propagation in the magnetosphere of Jupiter

A systematic procedure is developed for identifying the spatial regimes of various modes of wave propagation in the Jupiter magnetosphere that may be encountered by flyby missions. The Clemmow-Mullaly-Allis (CMA) diagram of plasma physics is utilized to identify the frequency regimes in which different modes of propagation occur in the magnetoplasma. The Gledhill model and the Ioannidis and Brice model of the magnetoplasma are summarized, and configuration-space CMA diagrams are constructed for each model for frequencies from 10 Hz to 1 MHz. The distinctive propagation features, the radio noise regimes, and the wave-particle interactions are discussed. It is concluded that the concentration of plasma in the equatorial plane makes this region of vital importance for radio observations with flyby missions. Local radio noise around the electron cyclotron frequency will probably differ appreciably from its terrestrial counterpart due to the lack of field-line guidance. Hydromagnetic wave properties at frequencies near the ion cyclotron frequency and below will probably be similar to the terrestrial case.

Liemohn, H. B.↗
NASA NTRS1972

Whistler side-band growth due to nonlinear wave-particle interaction.

The distortion caused by a large-amplitude whistler (with wave normal parallel to the static magnetic field) on the energetic-electron velocity distribution of a predominantly cold magnetoplasma is derived analytically. Whistler test waves impressed on the perturbed magnetoplasma and within two narrow bands centered on the frequency of the original wave may experience large consecutive growth at the early stages of the wave-particle interaction if the unperturbed energetic-electron distribution satisfies two specified conditions. The relevance of these whistler side bands to magnetospheric phenomena is assessed; in particular, an identification of the onset of artificially stimulated emissions with the creation of whistler side bands gives good agreement with observations.

Brinca, A. L.↗
NASA NTRS1979

Magnetosheath effects on cylindrical Langmuir probes

A study of the response of cylindrical Langmuir probes in magnetoplasmas focusing on the relative magnitudes of Larmor radius and sheath size is presented. The approach results in a classification of magnetic field effects which involves the magnetic field strength and plasma parameters of density, temperature, and the applied probe potential. It is shown that a 0.25 G field can have similar effects on the current collection properties of the probe in ionospheric plasma as a 30 kG field would have in a hot, dense laboratory plasma. The data also show: (1) the effects of probe orientation on electron current collection from magnetoplasmas; (2) that these effects can be important even when the electron Larmor radius is larger than the radius of the probe; and (3) that substantial magnetic field effects occur when the probe sheath is comparable to or greater than the Larmor radius.

Szuszczewicz, E. P.↗
NASA NTRS1986

Spontaneous radiation emitted by moving tethered systems

Some concepts related to radiation emitted by a large conductor moving through a magnetoplasma are outlined and referred to the case of long tethers. Some recent results of a theoretical calculation of Alfven wings, their structure and the power associated with are shown. How the problem of radiation from TSS or for any large conductor moving through a magnetoplasma should be approached is presented. The approach is that of the theory of antennas in plasmas.

Dobrowolny, M.↗
NASA NTRS1989

Influence of multiple ion species on low-frequency electromagnetic wave instabilities

The effect of multiple (singly ionized) coexisting newborn ion species on the stability of low-frequency electromagnetic waves was investigated using a plasma model in which solar wind magnetoplasma is made up of isotropic Maxwellian electron and proton populations with a common number density of 4.95/cu cm and temperatures equal to 17.2 eV and 6.9 eV, respectively. It is shown that the effect of multiple ions on wave growth, for given background magnetoplasma conditions and relative densities, depends not only on their mass but also on the physical nature of the wave modes. If the ion masses are disparate, each one of the coexisting ion beams tends to stimulate instabilities without undue influence from the other species. If the masses of newborn ions are similar, they can strongly catalyze wave growth of fluidlike nonresonant modes, but bring about weak growth enhancements in cyclotron resonant instabilities.

Brinca, Armando L.↗
NASA NTRS1991

Investigation of the structure of the electromagnetic field and related phenomena, generated by the Active Satellite

The altitude dependencies of the moduli of the electric field E in the VLF and LF frequency bands (f sub B much less than F less than f sub B) and in the altitude range of the ionosphere Z equals (400 to 2500) km up to Z equals 6000 km (the bottom of the magnetosphere) were calculated by the linear theory. The amplitudes of the field have large maxima in four regions: the axis field (E sub o) close to the direction of the Earth's magnetic field line B sub o, beta approximately 0 degrees, the fields (E sub St), (E sub RevSt) and (E sub Res) in the Storey, Reversed Story and Resonance cones, beta approximately (0 approaches 20) degrees. Their maxima are very pronounced close to the low hybrid frequency F sub L. The nonlinear heating of the magnetoplasma under the action of an electric field Ee (sup iwt) was recently expanded by the macroscopic theory by the author. The velocities, collision frequencies and temperatures of all the constituents of a magnetoplasma - electrons, ions, and neutral particles - are taken into account. Formulae and numerical results are presented for the ionosphere in the frequency band F equals (1 to 10 exp 4) kHz and altitude range Z approximately (100 - 1000) km. Some results of calculations by the self consistent solution of the basis system of equations are also discussed.

Alpert, Yakov L.↗
NASA NTRS1992

Investigation of the structure of the electromagnetic field and related phenomena, generated by the active satellite

A short review is given for the general frequency and angle distribution of the electric field radiated by an electric dipole E = E(sub 0)cos(omega)t, in a magnetoplasma. Detailed results of numerical calculations of (E) were made in the Very Low Frequency (VLF) and the Low Frequency (LF) bands 0.02f(sub b) is less than or equal to F is less than or equal to 0.5f(sub b) (F is approximately (4-500) kHz) in the ionosphere and magnetosphere in the altitude region Z = (800-6000) km; f(sub b) is the electron gyro-frequency of the plasmas in the discussed region f(sub b) is approximately equal to (1.1 to 0.2) MHz. The amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth's magnetic field line (B(sub 0)), it is the so called Axis field (E(sub 0)) and in the Storey (E(sub St)), Reversed Storey (E(sub RevSt)), and Resonance (E(sub Res)) Cones. The maximal values of E(sub 0), E(sub Res), and E(sub RevSt) are very pronounced close to the low hybrid frequency, F approximately F(sub L). The flux of the electric field is concentrated in very narrow regions, the apex angles of the cones delta(beta) is approximately equal to (0.1 - 1) degree. The enhancement and focusing of the electric field is growing up, especially quickly at Z greater than 800 km. At Z is greater than 1000 up to 6000 km, the relative value of (E), in comparison with its value at Z = 800 km is about (10(exp 2) to 10(exp 4)) times larger. Thus, the flux of VLF and LF electromagnetic waves in the Earth magnetoplasma produces and is guided by very narrow pencil beams, similar, let us say, to laser beams.

Alpert, Yakov L.↗
NASA NTRS1993

The cone structure and focusing of the electric field of VLF and LF waves at high altitudes of the ionosphere

This paper presents a short review of the frequency and angle dependencies of the electric field radiated by an electric dipole E = E(sub 0)cos(omega)t in a magnetoplasma and detailed results of numerical calculations of (E) in the VLF and LF frequency bands 0.02f(sub b) is less than or equal to F is less than or equal to 0.5f(sub b) in the ionosphere and magnetosphere in the altitude region Z = (800 - 6000) km (F is approximately (4 - 500) kHz and f(sub b) is approximately equal to (1.1 to 0.2) MHz is the electron gyro-frequency). The amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth magnetic field line B(sub 0) (it is the so called Axis field E(sub 0); in the Storey E(sub St); Reversed Storey E(sub RevSt); and Resonance E(sub Res) Cones. The maximal values of E(sub 0), E(sub Res), and E(sub Rev ST) are the most pronounced close to the low hybrid frequency, F is approximately F(sub L). The flux of the electric field is concentrated in very narrow regions, with the apexes angles of the cones delta(beta) is approximately (0.1 - 1) degree. The enhancement and focusing of the electric field increases with altitude starting at Z is greater than 800 km. At Z is greater than or equal to 1000 up to 6000 km, the relative value of E, in comparison with its value at Z equals 800 km is about (10(exp 2) to 10(exp 10)) times larger. Thus, the flux of VLF and LF electromagnetic waves in the Earth magnetoplasma produces and is guided by very narrow pencil beams, similar, let us say, to laser beams.

Alpert, Y. L.↗
NASA NTRS1993

On the stability of nongyrotropic ion populations - A first (analytic and simulation) assessment

The wave and dispersion equations for perturbations propagating parallel to an ambient magnetic field in magnetoplasmas with nongyrotropic ion populations show, in general, the occurrence of coupling between the parallel (left- and right-hand circularly polarized electromagnetic and longitudinal electrostatic) eigenmodes of the associated gyrotropic medium. These interactions provide a means to driving linearly one mode with free-energy sources of other modes in homogeneous media. Different types of nongyrotropy bring about distinct classes of coupling. The stability of a hydrogen magnetoplasma with anisotropic, nongyrotropic protons that only couple the electromagnetic modes to each other is investigated analytically (via solution of the derived dispersion equation) and numerically (via simulation with a hybrid code). Nongyrotropy enhances growth and enlarges the unstable spectral range relative to the corresponding gyrotropic situation. The relevance of the properties of nongyrotropic populations to space plasma environments is also discussed.

Brinca, A. L.↗
NASA NTRSDate not supplied

NTAC Augmented Nuclear and Advanced Propulsion

Currently, there are two types of nuclear propulsion: Nuclear Thermal Propulsion (NTP) and Nuclear Electric Propulsion (NEP). Common to both types, a nuclear reactor generates heat energy to raise the temperature of propellant, or the generated heat energy is converted into electric power. The electricity generated powers propulsion systems, such as a Hall thruster, magnetoplasma dynamic (MPD) thruster, or variable specific impulse magnetoplasma rocket (VASIMR). Customarily, only the thermal energy output from nuclear reaction is considered for NTP and NEP systems. However, the nuclear fission reaction can also generate ~7 MeV of prompt gamma rays. Therefore, most designers of NTP and NEP systems incorporate safety features to shield against this radiation. An optimized design approach would be to integrate a Nuclear Thermionic Avalanche Cell (NTAC) within the NTP or NEP structure for converting this radiation energy into additional electric power, while also shielding gamma rays. Consequently, this study addresses several combinations of NTP and NEP structures with NTAC devices in order to achieve that goal.

NTAC↗