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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Equilibria in Strongly Magnetized Pair Plasmas

Positron-electron pair densities for a thermal plasma in the steady-state equilibrium where pair production balances pair annihilation are found as a function of temperature kT / mc(2) approx. 1, source size R and magnetic field strength B. When the plasma is strongly magnetized, B 10(12) G, the important processes are synchrotron radiation, one-photon (magnetic) pair production and two-photon pair annihilation. An analytic solution for the equilibrium pair density, found under certain simplifying assumptions, shows that optically thin equilibria exist only for sufficiently small source sizes.

Harding, A. K.↗
NASA NTRS1976

Plasma kinetic processes in a strong d.c. magnetic field

Recent results in the kinetic theory of a strongly magnetized plasma are surveyed. Emphasis is on the electrostatic guiding-center plasma in two dimensions, in both the fluid and 'charged rod' descriptions. The basic kinetic description of the plasma is in terms of the statistically-distributed Fourier coefficients associated with the velocity and 'enstrophy' (charge density) fields. It is a universal tendency in such media for enstrophy to flow to shorter wavelengths but for energy to flow to longer wavelengths. A consequence of the energy flow to longer wavelengths is the generation of long-range order in the form of macroscopic vortices. These kinds of structure have been called 'convection cells' and can be extraordinarily efficient in transporting particles transverse to a magnetic field. The tendency to vortex formation can be disrupted by collisions between particles. Modifications of the Fokker-Planck equation for a plasma produced by a strong dc magnetic field are considered in both two and three dimensions.

Montgomery, D.↗
NASA NTRS1989

Antiproton powered propulsion with magnetically confined plasma engines

The reaction of the matter-antimatter annihilation, with its specific energy being over 250 times the specific energy released in nuclear fusion, is considered as an energy source for spacecraft propulsion. A concept of a magnetically confined pulsed plasma engine is described. In this concept, antiproton beams are injected axially into a pulsed magnetic mirror system, where they annihilate with an initially neutral hydrogen gas; the resulting charge annihilation products transfer energy to the hydrogen propellant, which is then exhausted through one end of the pulsed mirror system to provide thrust. Numerical simulations were developed to calculate the annihilation rate of antiprotons in hydrogen and to follow the resulting ion, muon, and electron/positron number density evolutions.

Lapointe, Michael R.↗
NASA NTRS1979

Investigation of the magnetospheric boundary plasma and magnetic field data from Explorers 33, 43, and 50

Understanding of the plasma depletion process in the dayside magnetosheath, the nature of magnetotail boundary motion, and the geometry of the magnetospheric boundary layers was examined. A model of the dayside boundary layers, based on the hypothesis that merging occurs only for strictly anitparallel fields was developed which provides a qualitative solution to the problem of the half-wave rectifier response of the magnetosphere to the solar wind electric field. Regarding magnetotail boundary motion, consideration of the data led to the conclusion that at lunar distance, substorms are associated with very large amplitude compressional wave motion of the sausage type. A study of IMF orientation for depletion and nondepletion cases suggests that depletion is most likely to occur for angles between the IMF and the normal to the magnetopause at the measurement location near 90 deg, in agreement with predictions. Observations of the heat flux in the dayside magnetosheath plasma suggest that the energized plasma ions have their source along a given flux tube at that intersection with the bow shock where the magnetic field is most compressed.

Siscoe, G. L.↗
NASA NTRS1974

Strongly magnetized classical plasma models

Discrete particle processes in the presence of a strong external magnetic field were investigated. These processes include equations of state and other equilibrium thermodynamic relations, thermal relaxation phenomena, transport properties, and microscopic statistical fluctuations in such quantities as the electric field and the charge density. Results from the equilibrium statistical mechanics of two-dimensional plasmas are discussed, along with nonequilibrium statistical mechanics of the electrostatic guiding-center plasma (a two-dimensional plasma model).

Montgomery, D.↗
NASA NTRS1978

Magnetically confined plasma solar collector

The possibility of using a plasma medium for collecting solar energy in space is examined on the basis of a concept involving an orbiting magnetic bottle in which a solar-energy-absorbing plasma is confined. A basic system uses monatomic cesium as working fluid. Cesium evaporates from a source and flows into the useful volume of a magnetic bottle where it is photoionized by solar radiation. Ions and electrons lost through the loss cones are processed by a recovery system, which might be a combination of electromagnetic devices and heat engines. This study concentrates on the plasma production processes and size requirements, estimates of the magnetic field required to confine the plasma, and an estimate of the system parameters for a 10 GW solar collector using cesium.

Walters, C. T.↗
NASA NTRS1981

Propagation in a shearing plasma. III - Magnetic field effects and pulsar microstructure periods

Effects of a magnetic field on wave and pulse propagation in a shearing plasma are investigated. Equations for the wave fields are derived from Maxwell's equations and the Minkowski relations for an anisotropic medium, when the magnetic field is parallel to the shearing velocity. The independent propagation modes are elliptically polarized in the stationary frame and vary with the velocity of the medium. Numerical calculations are presented which show the propagation of waves and pulses through a plane-parallel shearing plasma in the case of weak and strong fields. It is found that in a weak field, propagation effects are very similar to those previously found in field-free models: the transmitted pulses acquire temporal modulations whose period is frequency dependent. In a strong field, the period of the temporal modulations is independent of frequency. Transmitted pulses can also undergo polarization changes as a result of phase differences between modes. These results are discussed in relation to their significance to propagation in a pulsar magnetosphere and, in particular, to a model for pulse microstructure.

Harding, A. K.↗
NASA NTRS1979

Magnetic fields, plasmas, and coronal holes - The inner solar system

Recent results concerning streams and magnetic fields in the inner solar system are reviewed. Observations have shown that MHD streams are bounded by thin shear layers within 1 AU, probably because they originate in coronal holes which have sharp boundaries. The properties of Alfvenic fluctuations in streams cannot be fully explained on the basis of the hypothesis that they are plane, transverse Alfven waves. A more complete and accurate description might be that they represent nonplanar general Alfven waves weakly coupled to a compressive mode and moving through a medium containing tangential discontinuities and other convected inhomogeneities.

Burlaga, L. F.↗
NASA NTRS2001

Progress In Magnetized Target Fusion Driven by Plasma Liners

Magnetized target fusion (MTF) attempts to combine the favorable attributes of magnetic confinement fusion (MCF) for energy confinement with the attributes of inertial confinement fusion (ICF) for efficient compression heating and wall-free containment of the fusing plasma. It uses a material liner to compress and contain a magnetized plasma. For practical applications, standoff drivers to deliver the imploding momentum flux to the target plasma remotely are required. Spherically converging plasma jets have been proposed as standoff drivers for this purpose. The concept involves the dynamic formation of a spherical plasma liner by the merging of plasma jets, and the use of the liner so formed to compress a spheromak or a field reversed configuration (FRC).

Thio, Francis Y. C.↗
NASA NTRS2001

Magnetized Target Fusion Driven by Plasma Liners

Magnetized target fusion (MTF) attempts to combine the favorable attributes of magnetic confinement fusion (MCF) for energy confinement with the attributes of inertial confinement fusion (ICF) for efficient compression heating and wall-free containment of the fusing plasma. It uses a material liner to compress and contain a magnetized plasma. For practical applications, standoff drivers to deliver the imploding momentum flux to the target plasma remotely are required. Spherically converging plasma jets have been proposed as standoff drivers for this purpose. The concept involves the dynamic formation of a spherical plasma liner by the merging of plasma jets, and the use of the liner so formed to compress a spheromak or a field reversed configuration (FRC). For the successful implementation of the scheme, plasma jets of the requisite momentum flux density need to be produced. Their transport over sufficiently large distances (a few meters) needs to be assured. When they collide and merge into a liner, relative differences in velocity, density and temperature of the jets could give rise to instabilities in the development of the liner. Variation in the jet properties must be controlled to ensure that the growth rate of the instabilities are not significant over the time scale of the liner formation before engaging with the target plasma. On impact with the target plasma, some plasma interpenetration might occur between the liner and the target. The operating parameter space needs to be identified to ensure that a reasonably robust and conducting contact surface is formed between the liner and the target. A mismatch in the "impedance" between the liner and the target plasma could give rise to undesirable shock heating of the liner leading to increased entropy (thermal losses) in the liner. Any irregularities in the liner will accentuate the Rayleigh-Taylor instabilities during the compression of the target plasma by the liner.

Thio, Y. C. Francis↗
NASA NTRS2007

Large-Area Permanent-Magnet ECR Plasma Source

A 40-cm-diameter plasma device has been developed as a source of ions for material-processing and ion-thruster applications. Like the device described in the immediately preceding article, this device utilizes electron cyclotron resonance (ECR) excited by microwave power in a magnetic field to generate a plasma in an electrodeless (noncontact) manner and without need for an electrically insulating, microwave-transmissive window at the source. Hence, this device offers the same advantages of electrodeless, windowless design - low contamination and long operational life. The device generates a uniform, high-density plasma capable of sustaining uniform ion-current densities at its exit plane while operating at low pressure [<10(exp -4) torr (less than about 1.3 10(exp -2) Pa)] and input power <200 W at a frequency of 2.45 GHz. Though the prototype model operates at 2.45 GHz, operation at higher frequencies can be achieved by straightforward modification to the input microwave waveguide. Higher frequency operation may be desirable in those applications that require even higher background plasma densities. In the design of this ECR plasma source, there are no cumbersome, power-hungry electromagnets. The magnetic field in this device is generated by a permanent-magnet circuit that is optimized to generate resonance surfaces. The microwave power is injected on the centerline of the device. The resulting discharge plasma jumps into a "high mode" when the input power rises above 150 W. This mode is associated with elevated plasma density and high uniformity. The large area and uniformity of the plasma and the low operating pressure are well suited for such material-processing applications as etching and deposition on large silicon wafers. The high exit-plane ion-current density makes it possible to attain a high rate of etching or deposition. The plasma potential is <3 V low enough that there is little likelihood of sputtering, which, in plasma processing, is undesired because it is associated with erosion and contamination. The electron temperature is low and does not vary appreciably with power.

Foster, John E.↗
NASA NTRS1972

Strongly magnetized classical plasma models

The class of plasma processes for which the so-called Vlasov approximation is inadequate is investigated. Results from the equilibrium statistical mechanics of two-dimensional plasmas are derived. These results are independent of the presence of an external dc magnetic field. The nonequilibrium statistical mechanics of the electrostatic guiding-center plasma, a two-dimensional plasma model, is discussed. This model is then generalized to three dimensions. The guiding-center model is relaxed to include finite Larmor radius effects for a two-dimensional plasma.

Montgomery, D. C.↗