Trapped-electron effects on time-independent negative-bias states of a collisionless single-emitter plasma device: Theory and simulation

Crystal, T. L.; Gray, P. C.; Lawson, William S.; Birdsall, C.K.; Kühn, S.

doi:10.1063/1.859943

Cited by 20 publications

(4 citation statements)

References 12 publications

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“…Models developed for the thermionic converter were adapted to the Q-machine by Rynn [310] and Kuhn [311,312] who considered a variety of boundary conditions. Additional work has investigated the role of electrostatically trapped electrons [313,314]. A thorough investigation of the planar source and collector sheaths using both analytic modeling and PIC simulations was carried out by Schwager and Birdsall [121].…”

Section: Surfaces Emitting Plasma: the Q-machinementioning

confidence: 99%

Sheaths in laboratory and space plasmas

Robertson¹

2013

Plasma Phys. Control. Fusion

111

102

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The sheaths that occur at surfaces in laboratory and space plasmas are reviewed with an emphasis on numerical models that can be solved with modest computational resources. The surfaces in plasma may be the interior walls of confinement devices or inserted probes. Fluid and kinetic models are presented in some detail, and particle-in-cell models are discussed briefly. The numerical methods find the spatial profile of the potential, the particle densities near the surfaces and the current to the surfaces. Maxwellian electrons and cold ions are assumed at the outset and subsequently the models are expanded to encompass (1) multiple electron populations, (2) multiple ion species, (3) finite ion temperature, (4) surfaces that emit electrons such as heated cathodes or emissive probes and (5) surfaces that emit plasma as in the Q-machine. These complications may produce nonmonotonic sheaths in which the first derivative of the potential changes sign or double layers in which the second derivative changes sign. The effect of charge-exchange collisions on ion losses to the wall and on ion current to probes is discussed, but models with collisions of electron are omitted. Some recent advances are discussed, including experiments that measure the ion distribution function in sheaths using laser-induced fluorescence, experiments and numerical models on sheaths with multiple ion species and computational models of sheaths surrounding objects in flowing plasma.

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Section: Surfaces Emitting Plasma: the Q-machinementioning

confidence: 99%

Sheaths in laboratory and space plasmas

Robertson¹

2013

Plasma Phys. Control. Fusion

111

102

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“…This configuration has been studied extensively for instance to find steady state potential variations, some involving trapped plasma populations or "virtual cathodes." [5][6][7] For weaker magnetic fields the dynamics are changed since the particles are no longer confined to move along the magnetic field lines. 8 Our analysis emphasizes results relevant for Q-machines where L=k De > ffiffiffiffiffiffiffiffiffiffi M=m p in terms of the Debye length k De and the electron-ion mass ratio M/m, but the basic principles have more general applications, for instance for diodes.…”

Section: Introductionmentioning

confidence: 99%

Numerical studies of a plasma diode with external forcing

2012

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With reference to laboratory Q-machine studies we analyze the dynamics of a plasma diode under external forcing. Assuming a strong axial magnetic field, the problem is analyzed in one spatial dimension by a particle-in-cell code. The cathode is assumed to be operated in electron rich conditions, supplying an abundance of electrons. We compare different forcing schemes with the results obtained by solving the van der Pol equation. In one method of forcing we apply an oscillation in addition to the DC end plate bias and consider both amplitude and frequency variations. An alternative method of perturbation consists of modelling an absorbing grid at some internal position. Also in this case we can have a constant frequency with varying amplitude or alternatively an oscillation with chirped frequency but constant amplitude. We find that the overall features of the forced van der Pol equation are recovered, but the details in the plasma response need more attention to the harmonic responses, requiring extensions of the model equation. The analysis is extended by introducing collisional effects, where we emphasize charge exchange collisions of ions, since these processes usually have the largest cross sections and give significant modifications of the diode performance. In particular we find a reduction in oscillator frequency, although a linear scaling of the oscillation time with the system length remains also in this case. V C 2012 American Institute of Physics. [http://dx.

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“…Nevertheless it is ubiquitous in so-called bounded plasma systems [5] with a strong current [6]. In the meantime, the PRI and related phenomena have been studied by analytical methods [7] or by particle [8] and trajectory simulation [9]. PRI-like oscillations have been found in any system which can be approximated as a Pierce-type diode [10] or, more appropriately, as a low-density current-carrying BPS.…”

Section: Introductionmentioning

confidence: 99%

The effect of the collector sheath on the potential relaxation instability

Popa¹,

Schrittwieser²

1996

Plasma Phys. Control. Fusion

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The potential relaxation instability (PRI) can be excited in the magnetized plasma column of a single-ended Q-machine by drawing an electron current to a collector. This can either be the terminating tungsten plate (the cold plate (CP) or a grid (G) inserted in between. The frequency of the PRI, which according to the standard model should be solely determined by the length of the system, in fact also depends on the collector bias, the plasma density and the magnetic field. If, however, the reduction of the system length due to the electron-rich sheath in front of the collector is taken into account, in a certain range the PRI frequency becomes more independent of the external parameters.

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Trapped-electron effects on time-independent negative-bias states of a collisionless single-emitter plasma device: Theory and simulation

Cited by 20 publications

References 12 publications

Sheaths in laboratory and space plasmas

Sheaths in laboratory and space plasmas

Numerical studies of a plasma diode with external forcing

The effect of the collector sheath on the potential relaxation instability

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