Intrinsic Toroidal Rotation, Density Peaking, and Turbulence Regimes in the Core of Tokamak Plasmas

Observations in the ASDEX Upgrade tokamak show a correlation between the gradient of the intrinsic toroidal rotation profile and the logarithmic gradient of the electron density profile. The intrinsic toroidal rotation in the center of the plasma reverses from co- to countercurrent when the logarithmic density gradients are large, and the turbulence is either dominated by trapped electron modes or is at the transition between ion temperature gradient and trapped electron modes. A study based on local gyrokinetic calculations suggests that the dominant trend in the observations can be explained by the combination of residual stresses produced by $E\times B$ and profile shearing mechanisms.

Figure 1

Mach number at $r/a=0.2$ versus the normalized gradient $u^{\prime }$ at $r/a=0.45$ in $L$ and $H$ modes with OH and with auxiliary ion (ICH) and electron cyclotron heating (ECH).

Figure 2

$u^{\prime }$ (a), $R/L_{ne}$ and $T_e/T_i$ (b) versus ${\nu }_{\mathrm{eff}}$ (all at $r/a=0.45$), $R/L_{ne}$ at $r/a=0.45$ versus $q_{95}$ (c), and $u^{\prime }$ versus $R/L_{ne}$ (d) (both at $r/a=0.45$).

Figure 3

$R/L_{ne}$ (a) and $u^{\prime }$ (b) at $r/a=0.45$ versus the real frequency ${\omega }_r$ of the most unstable mode at $k_y{\rho }_i=0.3$.

Figure 4

Confinement time (a) and Mach number (b) at $r/a=0.25$ as a function of ${\nu }_{\mathrm{eff}}$ and toroidal rotation (c) and density (d) profiles of three cases identified by correspondent big open symbols in (a) and (b).

Figure 5

Local GS2 linear calculations of the contributions to $u^{\prime }$, due to ${\Gamma }_{\mathrm{RS}}$, assuming a tilting angle of $-0.3\mathrm{rad}$ (triangles pointing down), and from the Coriolis pinch (small squares), versus measured $R/L_{ne}$ (a), and the predicted values of $u^{\prime }$ (diamonds) versus measured $R/L_{ne}$ (a) and $u^{\prime }$ (b), in the TEM domain.