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  • 1
    Electronic Resource
    Electronic Resource
    Variational principle for optimal accelerated neutralized flow (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 56-58 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Minimizing the energy deposited in the electron current in neutralized flows, such as in the Hall thruster, is examined. Modifying the electron current along the channel by inserting emitting electrodes, can enhance the efficiency. By employing variational methods, an optimal electron current distribution is found. The efficiency enhancement due to this effect, however, is shown to be small. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331567
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  • 2
    Electronic Resource
    Electronic Resource
    The energy balance in the plasma of a coaxial plasma opening switch (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1133-1141 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The two-dimensional energy flow in the plasma of a coaxial plasma opening switch (POS), during the Hall-induced shock penetration of a magnetic field, is analyzed. The electron collisionality is assumed to be high enough that the dissipated magnetic-field energy becomes electron thermal energy. It is shown that that part of the magnetic-field energy (a third) that is dissipated at the cathode at the generator side of the plasma, becomes an electron kinetic energy, that is convected along the current channel. It is also shown that in the magnetized plasma magnetic-field energy flows backwards towards the generator. The third new result is that inside the shock front, electron thermal energy is converted into magnetic-field energy, contrary to the usual situation in shock waves in which field energy is converted into particle thermal energy. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872644
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  • 3
    Electronic Resource
    Electronic Resource
    Particle-in-cell simulations of fast magnetic field penetration into plasmas due to the Hall electric field (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3556-3563 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Particle-in-cell (PIC) simulations are used to study the penetration of magnetic field into plasmas in the electron-magnetohydrodynamic (EMHD) regime. These simulations represent the first definitive verification of EMHD with a PIC code. When ions are immobile, the PIC results reproduce many aspects of fluid treatments of the problem. However, the PIC results show a speed of penetration that is between 10% and 50% slower than predicted by one-dimensional fluid treatments. In addition, the PIC simulations show the formation of vortices in the electron flow behind the EMHD shock front. The size of these vortices is on the order of the collisionless electron skin depth and is closely coupled to the effects of electron inertia. An energy analysis shows that one-half the energy entering the plasma is stored as magnetic field energy while the other half is shared between internal plasma energy (thermal motion and electron vortices) and electron kinetic energy loss from the volume to the boundaries. The amount of internal plasma energy saturates after an initial transient phase so that late in time the rate that magnetic energy increases in the plasma is the same as the rate at which kinetic energy flows out through the boundaries. When ions are mobile it is observed that axial magnetic field penetration is followed by localized thinning in the ion density. The density thinning is produced by the large electrostatic fields that exist inside the electron vortices which act to reduce the space-charge imbalance necessary to support the vortices. This mechanism may play a role during the opening process of a plasma opening switch. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871946
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  • 4
    Electronic Resource
    Electronic Resource
    On the conduction of a current in a plasma-filled diode (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1296-1304 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two issues in plasma-filled diodes are addressed: electrostatic transient effects during the rise time of the current, and current neutralization in the bulk of the plasma. For the first issue an analytical method is used to recover some features of the diode behavior recently demonstrated in simulations [Phys. Fluids B 4, 3608 (1992)]. The potential and the electron flow are shown to be oscillatory at the initial phase of current rise, before ions start to move. The possibility of electron trapping in the potential hill is discussed. For the second issue an equilibrium is constructed that describes a plasma of dimensions larger than the electron skin depth. A beam of charged particles moves ballistically into the plasma and the plasma electrons generate a return current that neutralizes the beam current. When the plasma electrons reach the plasma boundary they bend into a skin layer and conduct the current along the plasma boundary. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871340
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  • 5
    Electronic Resource
    Electronic Resource
    Control of the electric-field profile in the Hall thruster (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 1048-1056 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Control of the electric-field profile in the Hall thruster through the positioning of an additional electrode along the channel is shown theoretically to enhance the efficiency. The reduction of the potential drop near the anode by use of the additional electrode increases the plasma density there, through the increase of the electron and ion transit times, causing the ionization in the vicinity of the anode to increase. The resulting separation of the ionization and acceleration regions increases the propellant and energy utilizations. An abrupt sonic transition is forced to occur at the axial location of the additional electrode, accompanied by the generation of a large (theoretically infinite) electric field. This ability to generate a large electric field at a specific location along the channel, in addition to the ability to specify the electric potential there, allows us further control of the electric-field profile in the thruster. In particular, when the electron temperature is high, a large abrupt voltage drop is induced at the vicinity of the additional electrode, a voltage drop that can comprise a significant part of the applied voltage. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1343508
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  • 6
    Electronic Resource
    Electronic Resource
    Spectroscopic investigations of the plasma behavior in a plasma opening switch experiment (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2122-2137 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron density, the electron kinetic energy, the particle motion, and electric fields in a coaxial positive-polarity plasma opening switch (POS) were studied using spectroscopic diagnostics. A gaseous source that injects the plasma radially outward from inside the inner POS electrode was developed. The plasma was locally seeded with various species, desired for the various measurements allowing for axial, radial, and azimuthal resolutions both prior to and during the 180 ns long current pulse. The electron density was determined from particle ionization times and the electron energy from line intensities and time dependent collisional-radiative calculations. Fluctuating electric fields were studied from Stark broadening. The ion velocity distributions were obtained from emission-line Doppler broadenings and shifts. The early ion motion, the relatively low ion velocities and the nearly linear velocity dependence on the ion charge-to-mass ratio, leads to the conclusion that the magnetic field penetrates the plasma early in the pulse. The ion velocity dependence on the axial location were thus used to infer the time dependent axial distribution of the magnetic field, indicating the formation of a relatively high current density at the load-side edge of the plasma. This is expected to cause plasma acceleration towards the load, found to be supported by charge-collector measurements. The fast magnetic field penetration could be explained by mechanisms based on the Hall effect. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871299
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  • 7
    Electronic Resource
    Electronic Resource
    Spectroscopic investigation of fast (ns) magnetic field penetration in a plasma (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2583-2589 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent magnetic field spatial distribution in a coaxial positive-polarity plasma opening switch (POS) carrying a current (approximately-equal-to)135 kA during (approximately-equal-to)100 ns, was investigated by two methods. In the first, ionic line emission was observed simultaneously for two polarizations to yield the Doppler and Zeeman contributions to the line profiles. In the second method, the axial velocity distribution of ions was determined, giving the magnetic field through the ion equation of motion. This method requires knowledge of the electron density, here obtained from the observed particle ionization times. To this end, a lower bound for the electron kinetic energy was determined using various line intensities and time-dependent collisional-radiative calculations. An important necessity for POS studies is the locality of all measurements in r, z, and θ. This was achieved by using laser evaporation to seed the plasma nonperturbingly with the species desired for the various measurements. The Zeeman splitting and the ion motion showed magnetic field penetration through the 3.5 cm long plasma at a velocity (approximately-equal-to)108 cm/s. The current density was found to be relatively high at the load-side edge of the switch plasma. It is suggested that this may cause plasma acceleration into the vacuum section toward the load, which is supported by charge-collector measurements. The fast magnetic field penetration agrees with estimates based on the Hall-field mechanism. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871220
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  • 8
    Electronic Resource
    Electronic Resource
    Fast decay of plasma return currents due to whistler waves (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2480-2487 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of the return current induced by a charged particle beam in a magnetized plasma is studied. The beam current is perpendicular to the background magnetic field. The return current is shown to depart from the beam along the background magnetic field with a whistler rather than a diffusion or an Alfvén velocity. In a plasma bounded by two conductors the return current oscillates with the whistler period. Analytical expressions for the evolution of the magnetic field and of the plasma return current are derived for a beam with a finite width and with various rise time dependences. When the whistler time is shorter than the rise time of the beam current, the plasma return current does not grow beyond the whistler time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870576
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  • 9
    Electronic Resource
    Electronic Resource
    Relativistic effects in energy extraction from alpha particles (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 138-145 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use in a tokamak of the recently reported relativistic two-gyrostream instability is investigated. The concept is evaluated with respect to the extraction of energy from relativistic ions in an inhomogeneous magnetized plasma by means of an electrostatic wave. For application to energetic alpha particle channeling in a tokamak fusion reactor, the relativistic two-gyrostream instability effects turn out to be relatively minor. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872124
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  • 10
    Electronic Resource
    Electronic Resource
    A vacuum sheath propagation along a cathode (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3111-3115 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The velocity of propagation of a vacuum sheath along the cathode is calculated. A regime of parameters is identified in which, surprisingly, this velocity is lower for higher currents. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871657
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