Toroidal Momentum Pinch Velocity due to the Coriolis Drift Effect on Small Scale Instabilities in a Toroidal Plasma

In this Letter, the influence of the “Coriolis drift” on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments.

Figure 1

$(R/2L_T){\Gamma }_{\varphi }/Q_i$ as a function of $u$ for three values of $k_{\theta }{\rho }_i$ 0.45 (○), 0.2 (□), and 0.7 (⋄). The top right graph shows the growth rate as a function of $u$ and the down left graph the contour lines of $(R/2L_T){\Gamma }_{\varphi }/Q_i$ as a function of $u$ and $u^{\prime }$, for $k_{\theta }{\rho }_i=0.2$ and 0.5, respectively.

Figure 2

$R{V}_{\varphi }/{\chi }_{\varphi }$ as a function of $R/L_N$ (+), $3\widehat{s}$ (*), $q$ (○), and $R/L_T-6$ (⋄), and $8k_{\theta }{\rho }_i$ (□).