Speaker
Description
Intrinsic rotation, a spontaneously generated toroidal plasma flow without external momentum input, is expected to play an important role in enhancing confinement by effectively suppressing plasma instabilities. Our previous work, (Kaang et al., PoP 2018) demonstrated that global electromagnetic (EM) effects induce mode asymmetry by gradually transforming the parity of EM-ITG modes from even to odd. The resulting asymmetry drives a finite EM parallel Reynolds stress, leading to intrinsic rotation.
In this work, we extend the previous study to investigate the profile shear effects by considering a wide range of safety factor and plasma temperature profiles. Global EM-ITG modes are obtained by solving the five-field fluid equations using the BOUT++ framework, and the EM parallel Reynolds stress is evaluated using linear EM-ITG eigenmodes within a quasi-linear model to analyze intrinsic rotation generation.
Our results show that intrinsic rotation is enhanced in plasmas characterized by weak magnetic shear and improved confinement. As the magnetic shear decreases, the parity ratio of EM-ITG modes changes more rapidly with increasing plasma beta(β=thermal energy/magnetic energy), leading to stronger mode asymmetry. Consequently, the EM parallel Reynolds stress is amplified, particularly in the high β regime. A steeper temperature gradient also amplifies the global EM effects on intrinsic rotation generation by enhancing parity mixing and the associated Reynolds stress. These findings are consistent with experimental observations (Rice et al., NF 2017), although nonlinear saturation and fully developed turbulence are not captured in the
present quasi-linear approach.