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

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10.1063/1.3658033

### 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 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 ρ_{ i }/σ. Blobs with remain coherent as they move through the scrape-off layer, whereas blobs with 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.

© 2011 American Institute of Physics

Received 14 July 2011
Accepted 07 November 2011
Published online 11 November 2011

Acknowledgments: The authors would like to thank M. Salewski for his helpful suggestions and his critical reading of the manuscript. This work was supported by the Danish Agency for Science, Technology and Innovation FNU Grant No. 09-062293. In the last stage of the work, J. Madsen was supported by an EFDA fusion researcher fellowship.

Article outline:

I. INTRODUCTION

II. GYROFLUID MODEL

A. Vorticity equation

1. Diffusion

B. Energy conservation

III. BLOBDYNAMICS

A. Initial condition

B. Interchange motions

C. Finite Larmor radius effects

IV. NUMERICAL RESULTS

A. General blobdynamics

1. Cold ions

2. Finite ion temperature

B. Blob transport

1. Center of mass

b.

c. n_{max}

d. Blob compactness

V. SUMMARY

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2011-11-11

2014-04-19

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