Abstract
The probability distribution function (PDF) tails of the zonal flow structure formation and the PDF tails of momentum flux are computed by incorporating the effect of a shear flow in ion-temperature-gradient (ITG) turbulence. The bipolar vortex soliton (modon) is assumed to be the coherent structure responsible for bursty and intermittent events driving the PDF tails. It is found that stronger zonal flows are generated in ITG turbulence than Hasegawa-Mima turbulence, as well as further from marginal stability. This suggests that although ITG turbulence has a higher level of heat flux, it also more likely generates stronger zonal flows, leading to a self-regulating system. It is also shown that shear flows can significantly reduce the PDF tails of Reynolds stress and structure formation.
| Original language | English |
|---|---|
| Article number | 082312 |
| Journal | Physics of Plasmas |
| Volume | 15 |
| Issue number | 8 |
| DOIs | |
| Publication status | Published - 8 Sept 2008 |
| Externally published | Yes |
Funding
This research was supported by the Engineering and Physical Sciences Research Council (EPSRC) EP/D064317/1. FIG. 1. The momentum flux PDF tail in ITG turbulence with the effects of shear flow. The parameters are η i = 4.0 , τ = 0.5 , ε n = 1.0 , g i = 1 , a = 2 , U = 2.0 , κ 0 = 3 × 10 3 , ε = 0.1 , k ≈ 1.91 with V 0 = 0.0 (blue line, solid line), V 0 = 4.0 (red line, dashed-dotted line), V 0 = 8.0 (black line, dotted line), V 0 = 12.0 (green line, dashed line), and V 0 = 16.0 (magenta line, thick solid line). FIG. 2. The PDF tail of structure formation as a function of zonal flow potential. The PDF tails ITG turbulence (blue line, solid line), forced Hasegawa–Mima (HM) turbulence (red line, dashed-dotted line), Gaussian distribution with the same parameters as for the ITG mode turbulence (green line, thick solid line) and cases with negative modon speed in ITG mode turbulence (dotted black line) and in HM turbulence (dashed black line). The parameters are η i = 4.0 , τ = 0.5 , ε n = 1.0 , g i = 1 , a = 2 , V 0 = 12.0 , U = 2.0 ( U = − 5.0 dotted black line and dashed black line), κ 0 = 3 × 10 3 , ε = 0.1 and k ≈ 1.84 (ITG case), k = 0.81 (ITG with reversed modon speed), k ≈ 1.73 (HM case), and k = 1.56 (HM with reversed modon speed). FIG. 3. The PDF tail of the structure formation as a function of zonal flow potential with zonal flow strength as a parameter. The resulting PDF tails are shown for V 0 = 0.0 (blue line, solid line), V 0 = 4.0 (red line, dashed-dotted line), V 0 = 8.0 (black line, dotted line), V 0 = 12.0 (green line, dashed line), and V 0 = 16.0 (magenta line, thick solid line). The other parameters are the same as in Fig. 1 . FIG. 4. The PDF tail of structure formation as a function of zonal flow potential with η i as a parameter. The PDF tails are shown for η i = 2.0 (red line, dashed line), η i = 4.0 (blue line, solid line), and η i = 6.0 (black line, dashed-dotted line). The parameters are V 0 = 14.0 , k ≈ 1.91 , U = 4.0 , and the others are as in Fig. 2 .
ASJC Scopus subject areas
- General Physics and Astronomy
- Condensed Matter Physics