DIKUL - logo
(UL)
  • Fluid and kinetic parameters near the plasma-sheath boundary for finite Debye lengths
    Jelić, Nikola ...
    In a recent paper by Kuhn et al. [Phys. Plasmas 13, 013503 (2006)], it has been demonstrated that in a plasma, the polytropic coefficient is a spatially varying quantity rather than a global constant ... as usually assumed in fluid theory. Assuming cold ion sources and using the asymptotic two-scale approximation (in which the ratio of the Debye length over the characteristic presheath length, , is set to zero), it was found that the profile exhibits asharp peak (with values roughly between 6 and 8) at the plasma-sheath boundary. In the present paper, it is shown that in a finite approach, this sharp peak is smoothed to a regular maximum, which for increasing (e.g., decreasing plasma density) decreases and finally disappears. In any case, assumptions like =1 and/or =3, which are customarily encountered in the context of fluid approaches, are disproved. Although the present results were obtained for collisionless plasmas, it is reasonable to assume that the behavior uncovered holds qualitatively for any plasma with cold ion sources. In addition to calculating time-independent theoretical solutions by means of an analytic-numerical approach, we primarily employ particle-in-cell (PIC) computer simulations, which intrinsically represent a time-dependent approach.It is confirmed that, although extreme care is required to separate physical from numerical effects, the PIC simulation method is a highly suitable tool also for future investigations of more demanding physical scenarios assuming, e.g., warm ion sources and other more complex aspects thatcannot be treated realistically by analytic-numerical means alone. In addition, the extension from time-independent analytic-numerical calculation to time-dependent simulation permits us also to investigate the effect of collective plasma oscillations on the ion velocity distribution function (VDF). Although the ion VDFs obtained in our PIC simulations visibly differ insome details from the time-independent theoretical ones, the related ion-temperature and profiles turn out to fit their theoretical counterparts very well over significant parameter ranges. Hence, the two methods may to some extent be applied as alternative ones in future investigations on the plasma-sheath transition.
    Vir: Physics of plasmas. - ISSN 1070-664X (Letn. 14, 2007, 9 str.)
    Vrsta gradiva - članek, sestavni del
    Leto - 2007
    Jezik - angleški
    COBISS.SI-ID - 10215195

    Povezava(-e):

    http://dx.doi.org/10.1063/1.2793737

vir: Physics of plasmas. - ISSN 1070-664X (Letn. 14, 2007, 9 str.)

loading ...
loading ...
loading ...

Vnos na polico