The influence of finite Larmor radius effects on the radial interchange motions of plasma filaments

Jens Madsen, Odd E. Garcia, Jeppe Stærk Larsen, Volker Naulin, Anders Henry Nielsen, Jens Juul Rasmussen

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    The influence of finite Larmor radius (FLR) effects on the perpendicular convection of isolated particle density filaments driven by interchange motions in magnetized plasmas is investigated using a two-moment gyrofluid model. By means of numerical simulations on a two-dimensional, bi-periodic domain perpendicular to the magnetic field, it is demonstrated that the radial velocities of the blob-like filaments are roughly described by the inertial scaling, which prescribes a velocity proportional to the square root of the summed electron and ion pressures times the square root of the blob width. Due to FLR effects, the poloidal up-down symmetry in the particle density field observed in the zero Larmor radius limit is broken. The symmetry breaking implies a poloidal motion of the blobs in the BrB direction. At later times, the direction of the poloidal motion is reversed when the blob is decelerated. It is shown that the spatial structure of the blobs depends on the ratio of the ion gyroradius to the initial filament size qi=r. Blobs with qi=r&0:2 remain coherent as they move through the scrape-off layer, whereas blobs with qi=r.0:1 form plume-like structures that loose their coherence and eventually become fragmented. After having traveled approximately five times their initial widths, coherent blobs carry 2–3 times the particle density of fragmented blobs. It is shown that FLR effects reduce mixing, stretching, and generation of small spatial scales in the particle density field by setting up a sheared flow surrounding the blob.
    Original languageEnglish
    JournalPhysics of Plasmas
    Volume18
    Pages (from-to)112504
    ISSN1070-664X
    DOIs
    Publication statusPublished - 2011

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