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  • 1
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    Ion-acoustic waves in a plasma with negative ions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Propagation and damping of ion-acoustic waves have been investigated in a Q-machine plasma consisting of K(+) positive ions, SF6(-) negative ions, and electrons. The phase velocity of the ion-acoustic 'fast' mode increases with increasing epsilon, the concentration of negative ions. The wave damping decreases with increasing epsilon, and nearly disappears, for the highest wave frequencies investigated, when epsilon is more than about 0.9. Both results are in agreement with predictions from Vlasov theory.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids B (ISSN 0899-8221); 3; 284-287
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    NASA TECHNICAL REPORTS
  • 2
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    Electrostatic ion-cyclotron waves in a two-ion component plasma (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The excitation of electrostatic ion cyclotron (EIC) waves is studied in a single-ended Q machine in a two-ion component plasma (Ca+ and K+). Over a large range of relative concentrations of Cs+ and K+ ions, two modes are excited with frequencies greater than the respective cyclotron frequencies of the ions. The results are discussed in terms of a fluid theory of electrostatic ion cyclotron waves in a two-ion component plasma.
    Keywords: PLASMA PHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 16; 396-398
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  • 3
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    Transition from moving to stationary double layers in a single-ended Q machine (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Large-amplitude (less than about 100 percent) relaxation oscillations in the plasma potential are known to be generated when the cold endplate of a single-ended Q machine is biased positively. These oscillations are associated with double layers that form near the hot plate (plasma source) and travel toward the endplate at about the ion-acoustic velocity. At the endplate they dissolve and then form again near the hot plate, the entire process repeating itself in a regular manner. By admitting a sufficient amount of neutral gas into the system, the moving double layers were slowed down and eventually stopped. The production of stationary double layers requires an ion source on the high-potential side of the double layers. These ions are provided by ionization of the neutral gas by electrons that are accelerated through the double layer. The dependence of the critical neutral gas pressure required for stationary double-layer formation on endplate voltage, magnetic field strength, and neutral atom mass has been examined. These results are discussed in terms of a simple model of ion production and loss, including ion losses across the magnetic field.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids B (ISSN 0899-8221); 2; 1936-194
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  • 4
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    Ion-beam focusing in a double-plasma device (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The authors studied the propagation of a low-energy charge-neutralized ion beam injected into the target region of a long double-plasma device. A magnetic field of up to about 180 G may be applied along the axis of the device. As a result of charge exchange collisions, the ion beam is attenuated as it propagates into the target region. However, under certain conditions of magnetic field strength and neutral gas pressure, the authors have observed a `reemergence' of the beam on axis far downstream in the target. This reemergence of the ion beam is attributed to a focusing of the ions by a self-consistently produced radial ambipolar electric field. The effect may be expected to occur in other types of plasma devices as well, whenever a sufficiently large radially inward electric field is present.
    Keywords: PLASMA PHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 16; 590-596
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  • 5
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    Plasma density fluctuations observed during Space Shuttle Orbiter water releases (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observations by the Langmuir probe on the Plasma Diagnostics Package flown as part of the Spacelab 2 mission in the summer of 1985 show a strong increase in the level of turbulence near the Shuttle Orbiter during operations in which liquid water is released. The spectrum of the plasma density fluctuations peaks at the lowest frequencies measured (a few Hz) and extends up to a few kHz, near the lower hybrid frequency. Two potential mechanisms for generating the plasma turbulence are suggested which are both based on the production of water ions as a result of charge exchange with the ambient oxygen ions in the ionosphere. The first mechanism proposed is the ion-plasma instability which arises from the drift of the contaminant with respect to the ambient oxygen ions. The other mechanism proposed is the Ott-Farley instability, which is a result of the ring distribution formed by the 'pick-up' water ions.
    Keywords: PLASMA PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 12081-12
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  • 6
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    Plasma density, temperature and turbulence in the wake of the Shuttle Orbiter (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: In situ observations of the plasma density, temperature, and turbulence in the near wake, midwake, and far wake of the Shuttle Orbiter are presented. The results show that the plasma disturbances produced by the passage of the Orbiter extend downstream for a distance of several hundred meters behind the Orbiter. It is found that the electron density profile exhibits nonmonotonic behavior, and that most of the 6-40-Hz turbulence in the wake is confined to a region about 20 m downstream of the Orbiter. The saturation Delta N(e)/N(e) spectra rapidly decline in the 10,000-100,000-Hz decade, both in the ambient ionosphere and in the wake.
    Keywords: PLASMA PHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 37; 1001-101
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  • 7
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    Influence of the ion/neutral atom mass ratio on the damping of electrostatic ion-cyclotron waves (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The damping of electrostatic ion-cyclotron waves by ion-neutral collisions was studied in a single-ended Q machine. The amplitudes of K(+) and Cs(+) electrostatic ion-cyclotron waves were measured as a function of neutral pressure in helium, neon, argon, krypton, and xenon. For each ion/neutral atom combination, the electrostatic ion-cyclotron wave amplitude maximizes at a neutral pressure that scales monotonically with the m(+)/m(n) mass ratio. This result is interpreted by considering the dynamics of elastic collisions between the ions and the neutral atoms.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids (ISSN 0031-9171); 30; 3304-330
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  • 8
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    Exposed high-voltage source effect on the potential of an ionospheric satellite (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A pulsed, high-voltage source, which is able to draw a current from the surrounding plasma, is seen to induce large changes in the potential of an ionospheric satellite (the Iowa Plasma Diagnostics Package flown on Space Shuttle flight STS-51F). This, in turn, may affect the operation of other instruments that use the chassis of the satellite as a ground for electrical circuits. The magnitude of the change in satellite potential is dependent upon both the orientation of the high-voltage source, relative to the plasma flow, and the characteristics of the high-voltage source. When the satellite is grounded to the Shuttle Orbiter, this effect is sufficient to change the potential of the Orbiter by a small, but noticeable, amount.
    Keywords: PLASMA PHYSICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 25; 64-69
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  • 9
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    The effect of a magnetic field gradient on anode double layers (1992)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: In experiments on anode (ionization) double layers in nonuniform magnetic fields it has been noted that the magnetic field gradient seems to stabilize the double layer position. This effect is further investigated in a Q machine in which the magnetic field geometry could be varied. It is found that the position of the double layers, along the axis of the device, could be controlled by changing the magnetic geometry. This effect is accounted for in a physical model which takes into account the effect of ion reflection by the magnetic mirror force in the region of magnetic field nonuniformity. This model is also able to account for variation of the double layer position when the neutral gas pressure is varied.
    Keywords: PLASMA PHYSICS
    Type: Physica Scripta (ISSN 0031-8949); 45; 395-398
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  • 10
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    On the stability of strong double layers (1992)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: For a strong, stationary double layer to be maintained, the electron flux Phi(e) and the ion flux Phi(i) must satisfy the Langmuir condition Phi(e)/Phi(i) = sq rt m(i)/m(e). However, this condition alone does not determine whether or not the double layer will remain in stable equilibrium at a given position. A new stability condition is obtained, and the results of several laboratory double layer experiments are examined using this condition.
    Keywords: PLASMA PHYSICS
    Type: Physica Scripta (ISSN 0031-8949); 45; 391-394
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