Geometric curvature effect on suppressing the Ion-Temperature-Gradient mode near the magnetic axis

TL;DR

This paper uses gyrokinetic simulations to reveal how geometric curvature and electric fields near the magnetic axis influence ion-temperature-gradient modes, shedding light on internal transport barrier formation.

Contribution

It uncovers the role of geometric curvature in modulating $E imes B$ shear and wave numbers, explaining mode suppression near the magnetic axis.

Findings

Radial electric field upshifts critical temperature gradient near the axis.

Geometric curvature significantly affects $E imes B$ shear and wave number.

High-n modes are suppressed by $E_r$, low-n modes by magnetic shear.

Abstract

Global gyrokinetic simulation of the ion temperature gradient mode shows that the radial electric field ($E_r$) well upshifts the critical temperature gradient near the magnetic axis, in the weak but not in the strong magnetic shear configuration. The geometric curvature effect significantly influences the $E \times B$ shear and the wave number near the axis, so that the $E_r$ well suppresses the high-n modes but has little effect on the low-n modes, which are suppressed by the weak magnetic shear effect. This new finding unravels the formation mechanism of the internal transport barrier in the weak central magnetic shear discharges.