Short wavelength ion temperature gradient mode in tokamak plasmas with hollow density profiles

Abstract

By the gyrokinetic integral eigenmode equation, we numerically investigate the short-wavelength ion-temperature-gradient (SWITG) mode in tokamak plasmas with hollow density profiles. This paper finds that the critical ion temperature gradient (ITG) R/LTiC exists for the hollow density profile. Over such a gradient, the SWITG mode is unstable. The R/LTiC for a hollow density profile is slightly lower than that for a peaked density profile, though far away from the threshold, the mode in the latter case is more unstable. Furthermore, the scaling of the ITG threshold increasing with ion-to-electron temperature ratio Ti/Te has been calculated, suggesting that the SWITG mode is more difficult to excite in hot ion plasmas as compared with that in hot electron plasmas. For the slightly hollow density profiles, it is shown that in the case of flat (peaked) electron temperature profiles, the SWITG modes are destabilized (stabilized) by the trapped electrons. For the steep hollow density profiles, however, the trapped electrons reduce the growth rate substantially, and thus, the SWITG stability threshold is raised significantly. In addition, the dependence of the threshold on local plasma parameters is analyzed in detail. It is found that the SWITG modes become more unstable for the high safety factor, small Larmor radius, weak magnetic shear, and high electron-to-ion temperature ratio.

Tungsten impurity effects on the coupling of TEM and ITG mode in reversed magnetic shear tokamak plasmas

“…The results summarized above suggest that the short wavelength ITG mode of L ez = 2.0 is difficult to be excited when η i = 5.0. Furthermore, the results in [46] imply that the shapes of k θ ρ s spectra are also related to the values of ITG, supporting the conjecture that the second peak will appear to form double humps in the short wavelength regime contributed by a larger value of ITG. obvious that the eigenmodes are well localized in the low magnetic field side with extrema at θ = 0 and converged around θ = ±3.3 and ± 3.5 for the TEM and ITG mode, respectively, which indicates that the ITG mode has a broader structure than the TEM due to the oscillation along the field line.…”

Analysis of anomalous transport based on radial fractional diffusion equation

“…Moreover, in Tore Supra, heat pinch effect was also observed and this effect was enhanced in low-density discharge [12]. Further, hollow density profiles have been observed during the fueling processes in some devices [13,14], and the related micro-turbulence studies have also been done [15][16][17], as well as the hollow profiles of impurities [18][19][20]. Some simulations showed that tracer particles were trapped in eddies or jumped over several eddies in a single flight in a plasma with pressure-gradient-driven turbulence.…”