Identification of electrostatic microinstability maps in quasi-axisymmetric stellarator

Abstract

Microinstabilities such as ion temperature gradient (ITG) mode and trapped electron mode (TEM) in quasi-axisymmetric (QA) stellarator are investigated by using gyrokinetic Vlasov simulations, where the QA configuration of Chinese first quasi-axisymmetric stellarator is utilized. Extensive parameter scans with respect to the density and temperature gradients for the zero beta cases identify the microinstability maps that indicate the transition boundary among ITG and TEM. It is found that, in particular for the modes with the ion-gyroradius scale, a relatively more stabilized regime appears along the transition boundary of ITG–TEM. Such a valley-like stability structure is not observed in the other cases with the sub-ion-gyroradius-scale. A stabilization effect attributed to the hollow density profile is also demonstrated.