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Anomalous parallel momentum transport due to flow shear in a tokamak plasma
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Image of FIG. 1.
FIG. 1.

Adiabatic ITG growth rate spectra for different values of . For values of , the spectrum peaks at lower .

Image of FIG. 2.
FIG. 2.

Time traces of ion heat diffusivity and momentum flux for the restart method (blue, thin) compared to a run without restart (orange, thick) with with means and variances and for the restart and nonrestart methods, respectively.

Image of FIG. 3.
FIG. 3.

convergence check of the shearing implemented in GKW, with held constant. The test is most important for small values of ; here . The values of the averages over are , , and , with increasing .

Image of FIG. 4.
FIG. 4.

GKW benchmark of background shear with GYRO. Anomalous ion heat diffusivity against . GKW results (diamonds) for (a) adiabatic electrons, (b) kinetic electrons, and (c) adiabatic with are compared to the equivalent GYRO results (circles) from Tables II, III, IV, and V of Ref. 16. The dashed lines in (a) include coupled parallel velocity shear for purely toroidal rotation with .

Image of FIG. 5.
FIG. 5.

Comparison of anomalous ion heat diffusivity for the standard and extended binormal resolution with up to 2.05 resolved. The standard resolution is sufficient except in the region near to the critical shear.

Image of FIG. 6.
FIG. 6.

Heat diffusivity against .

Image of FIG. 7.
FIG. 7.

Variation of shear quench parameter with magnetic shear . Linear fit has equation .

Image of FIG. 8.
FIG. 8.

Time averaged perturbed parallel potential showing increasing asymmetry with increasing . For negative the direction of the shift is reversed. The case shown has . The shift is always in the direction of . is the parallel coordinate.

Image of FIG. 9.
FIG. 9.

Momentum transport due to shear contribution for different values of . Legend as for Figs. 1, 6, and 11.

Image of FIG. 10.
FIG. 10.

Momentum transport due to shear contribution normalized with heat diffusivity for different values of . Legend as for Figs. 1, 6, and 11.

Image of FIG. 11.
FIG. 11.

Momentum fluxes normalized with heat diffusivity and for different values of .

Image of FIG. 12.
FIG. 12.

against for various .

Image of FIG. 13.
FIG. 13.

(upper) converges to the estimated Prandtl number (middle). The curve for (circles) is the same in the top two figures. (lower) is only independent of for small values of . The legend is the same for all three figures. The linear fits used in the bottom figure are (dashed, solid).

Image of FIG. 14.
FIG. 14.

Effective momentum diffusivity for cases with purely toroidal rotation . The aspect ratio was varied between 0.16, 0.20, and 0.25, with the safety factor unchanged.

Image of FIG. 15.
FIG. 15.

(Top) Comparison of normalized for kinetic electrons and adiabatic electrons. (Bottom) Parallel perturbed potential structures compared. The trapped electron drive is localized on the outboard side, but the asymmetric shift is equivalent.


Generic image for table
Table I.

Most unstable linear modes: Growth rate , with corresponding mode frequency and scale . Positive values of indicate propagation in the ion diamagnetic direction.

Generic image for table
Table II.

Representative nonlinear results for with mean and variance of saturated quantities.

Generic image for table
Table III.

Representative nonlinear results for with mean and variance of time averaged saturated quantities.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Anomalous parallel momentum transport due to E×B flow shear in a tokamak plasma