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Two-dimensional modelling of blob dynamics in tokamak edge plasmas
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic view of 3D blob geometry. (a) Blob sits on the magnetic field lines going through conductive material surfaces. (b) Blob sits on highly bending magnetic field lines getting into SOL region without touching the material target.

Image of FIG. 2.
FIG. 2.

A density contour plot of an initial blob . The darker area means higher density. It could be seen as an initial snapshot of any blob simulation in this paper.

Image of FIG. 3.
FIG. 3.

The RI-SOL blob motion for , 1, 2, 5 in (a), (b), (c), (d) with , respectively. Blob motion mode is very sensitive to the blob size around unity. blob goes to mushroom shape by strong velocity shear; blob goes to fingering shape by effective gravitational force; and the blob is the most stable one and coherently moves to a very long distance.

Image of FIG. 4.
FIG. 4.

The RI-SOL blob motion for with and zero potential at . It has a smaller curvature, smoother back edge, and longer evolution time than the one in Fig. 3(a)(2). However, we still see the small-scale blob motion accompanied by the mushroom structure.

Image of FIG. 5.
FIG. 5.

The FI-SOL blob motion for in (a), (b), (c), (d) with all . Comparing the RI-SOL results at the same time stage, and , the FI blob motions have mushroom shapes that are highly suppressed. The blob goes to the finger effect. The blob motion does not change much between FI and RI results, because the inertia term is negligibly small in this large size case.

Image of FIG. 6.
FIG. 6.

Blob’s peak position vs time in the FI-SOL case with the square dotted line and the RI-SOL case with the circle dotted line. The small FI blob keeps constant velocity better than the small RI blob because the RI blob’s speed is slowed down by the strong velocity shear, i.e., the mushroom effect. This is coincident with the mushroom suppression in the FI results.

Image of FIG. 7.
FIG. 7.

The HB blob motion for in (a), (b), (c), (d) with , respectively. The motion modes or the patterns of these HB blobs are different from the SOL blobs. We do not see the mushroom shape or the fingering shape in (b)–(d) compared to Figs. 3(a), 3(b), and 3(d). However, mushrooms show up in the extremely small structure such as in (a) and fingers can be observed in the large blob evolution with sufficiently steep leading edge.

Image of FIG. 8.
FIG. 8.

Peak position vs time of the HB blob with different sizes. We use for each blob to rescale its own and time axes. This rescaling is only for resizing the figure and containing all four blobs’ position-time figure suitably in one figure. It does not change the curve’s slope, which stands for the velocity of the moving blob.

Image of FIG. 9.
FIG. 9.

The density profile at the center line of the blob with different diffusivities. In (a), the SOL case, the dotted line is for the dimensionless , the solid line is for , the dotted-dashed line is for . In (b), the HB case, the dotted line is for , the solid line is for , the dotted-dashed line is for . Diffusivity does not change the blob motion modes much in both cases.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Two-dimensional modelling of blob dynamics in tokamak edge plasmas