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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1669-1675 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-and-one-half-dimensional electrostatic particle simulation model has been developed to study neutral gas release experiments into the ionosphere. The electrons are assumed guiding center particles, while the full dynamics of the ions (with real masses) are followed in time and space. Ionization processes of the neutral gas by charge exchange and electron impact are included by means of the Monte Carlo technique. It is shown that the model can be used to simulate the neutral gas interaction, with the ionosphere using realistic experimental parameters. The model was applied to study the critical ionization velocity (CIV) tests recently conducted as part of the ATLAS-1 [Geophys. Res. Lett. 20, 499 (1993)] xenon gas releases from the space shuttle. The simulation results show suprathermal electrons produced by an ion beam-driven lower hybrid instability, create a xenon ion population much more rapidly than the production by classical processes, indicating the prevalence of a CIV-type mechanism.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2191-2196 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental and theoretical research has been initiated at the Princeton Plasma Physics Laboratory on the electrostatic atomization process in collaboration with Charged Injection Corporation. The goal of this collaboration is to set up a comprehensive research and development program on the electrostatic atomization at the Princeton Plasma Physics Laboratory so that both institutions can benefit from the collaboration. Experimental, theoretical and numerical simulation approaches are used for this purpose. An experiment consisting of a capillary sprayer combined with a quadrupole mass filter and a charge detector was installed at the Electrostatic Atomization Laboratory to study fundamental properties of the charged droplets such as the distribution of charges with respect to the droplet radius. In addition, a numerical simulation model is used to study interaction of beam electrons with atmospheric pressure water vapor, supporting an effort to develop an electrostatic water mist fire-fighting nozzle. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3312-3321 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Injection of a neutral beam into a plasma in a magnetic field has been studied by means of numerical plasma simulations. It is found that, in the absence of a rotational transform, the convection electric field arising from the polarization charges at the edges of the beam is dissipated by turbulent plasma convection, leading to anomalous plasma diffusion across the magnetic field. The convection electric field increases with the beam density and beam energy. In the presence of a rotational transform, polarization charges can be neutralized by the electron motion along the magnetic field. Even in the presence of a rotational transform, a steady-state convection electric field and hence anomalous plasma diffusion can develop when a neutral beam is constantly injected into a plasma. Theoretical investigations of the convection electric field are described for a plasma in the presence of a rotational transform.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 209-220 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Injection of a nonrelativistic electron beam into a fully ionized plasma from a spacecraft including the effect of charging has been studied using a one-dimensional particle simulation model. It is found that the spacecraft charging remains negligible and the beam can propagate into a plasma, if the beam density is much smaller than the ambient density. When the injection current is increased by increasing the beam density, significant spacecraft charging takes place and the reflection of beam electrons back to the spacecraft reduces the beam current significantly. On the other hand, if the injection current is increased by increasing the beam energy, spacecraft charging remains negligible and a beam current much larger than the thermal return current can be injected. It is shown that the electric field caused by the beam–plasma instability accelerates the ambient electrons toward the spacecraft thereby enhancing the return current.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 1772-1778 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mode conversion near the upper-hybrid resonance frequency and electron heating are studied using a one-dimensional electromagnetic relativistic particle code. It is found that for a sufficiently small pump field E0, E20/4πnTe (approximately-less-than)0.01, electron heating is localized in a region near the electron cyclotron layer where the pump frequency is equal to the local electron gyrofrequency. For stronger pump fields, electron heating takes place more or less uniformly across a region between the upper-hybrid resonance layer and the cyclotron layer. In addition, a significant fraction of electromagnetic energy associated with the pump is found to be reflected back into the vacuum from a region in the plasma near the upper-hybrid resonance layer for both strong (E20/4πnTe ≈1) and weak pumps (E20/4πnTe (very-much-less-than)1).
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 3365-3379 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One- and two-dimensional particle simulations of beam–plasma interaction have been carried out in order to understand current drive experiments that use an electron beam injected into the Advanced Concepts Torus (ACT)-1 device [Rev. Sci. Instrum. 53, 409 (1982)]. Typically, the initial beam velocity along the magnetic field is V0=109 cm/sec, while the thermal velocity of the background electrons is vt=108 cm/sec. The ratio of the beam density to the background density is about 10% so a strong beam–plasma instability develops, causing rapid diffusion of beam particles. For both one- and two-dimensional simulations, it is found that a significant amount of beam and background electrons are accelerated considerably beyond the initial beam velocity when the beam density is more than a few percent of the background plasma density. In addition, the electron distribution along the magnetic field has a smooth negative slope, f'(v(parallel))〈0, for v(parallel)〉0 extending to v(parallel)=1.5 V0∼2 V0, which is in sharp contrast to the predictions from quasilinear theory. An estimate of the mean-free path for beam electrons caused by Coulomb collisions reveals that the beam electrons can propagate a much longer distance than is predicted from a quasilinear theory because of the presence of a high-energy tail. These simulation results agree well with the experimental observations from the ACT-1 device.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1160-1168 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional numerical plasma simulations have been carried out in a uniform magnetic field to study the effects of neutral beam injection on plasma diffusion. Neutral beams injected across a magnetic field are assumed to be ionized by various ionization processes in a plasma. It is found that the suprathermal convective motion of a plasma generated by the injection of neutral beams is dissipated via anomalous viscosity, leading to enhanced cross-field diffusion. The diffusion coefficient depends weakly on the magnetic field and plasma density, similar to the diffusion caused by thermally excited convective cells. The magnitude of the diffusion increases with the injection energy and is much larger than the thermal diffusion because of the presence of suprathermal plasma convection. It is shown that a similar anomalous plasma diffusion may occur in a plasma subject to radio frequency (rf) wave heating where only a localized region of a plasma across the magnetic field is heated to a temperature much higher than the surrounding temperature. Theoretical investigations are described on the scaling of enhanced plasma diffusion.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 200-208 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Propagation of a nonrelativistic electron beam in a plasma in a strong magnetic field has been studied using electrostatic one-dimensional particle simulation models. Electron beams of finite pulse length and of continuous injection are followed in time to study the effects of beam–plasma interaction on the beam propagation. For the case of pulsed beam propagation, it is found that the beam distribution rapidly spreads in velocity space generating a plateaulike distribution with a high energy tail extending beyond the initial beam velocity. This rapid diffusion takes place within a several amplification length of the beam–plasma instability given by (ωpω2b) −1/3V0, where ωp, ωb, and V0 are the target plasma, beam–plasma frequencies, and the beam drift speed. This plateaulike distribution, however, becomes unstable as the high energy tail electrons free-stream, generating a secondary beam. A similar process is observed to take place for the case of continuous beam injection when the beam density is small compared with the total density nb/nt〈1. In particular, the electron velocity distribution is found monotonically decreasing in energy, having a high energy tail whose energy reaches twice the initial beam energy. Such an electron distribution is also seen in laboratory experiments and in computer simulations performed for a uniform, periodic system. When the beam density is increased so that the beam current exceeds the thermal return current, enbV0(approximately-greater-than)enevt, where ne and vt are the density and thermal speed of the ambient electrons, beam propagation becomes much slower due to the electric field generated by the excess charges associated with the beam electrons.Beam electrons are reflected from the ambient plasma as if they are bouncing off a rigid wall. When the beam velocity is increased while holding the beam density constant, simulations show that the beam current can exceed significantly the return current generated by the thermal electrons enevt. It is shown that the electric field generated by the beam–plasma instability accelerates the ambient electrons opposite to the beam propagation, thereby enhancing the return current.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1818-1821 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The diffusion of electrons across a magnetic field in the presence of a beam–plasma instability has been studied by means of two-dimensional numerical simulations. It is found that the beam electrons can diffuse much faster across the magnetic field than the thermal electrons. This can be explained by the fact that the electrons in the beam are in resonance with the waves excited by the beam–plasma instability so that they experience a nearly d.c. electric field, causing large cE×B/B2 excursions.
    Type of Medium: Electronic Resource
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