Collisionless zonal-flow dynamics in quasisymmetric stellarators
arXiv:2407.19592 · doi:10.1017/S0022377824001739
Abstract
The linear collisionless plasma response to a zonal-density perturbation in quasisymmetric stellarators is studied, including the geodesic-acoustic-mode oscillations and the Rosenbluth--Hinton residual flow. While the geodesic-acoustic-mode oscillations in quasiaxisymmetric configurations are similar to tokamaks, they become non-existent in quasi-helically symmetric configurations when the effective safety factor in helical-angle coordinates is small. Compared with concentric circular tokamaks, the Rosenbluth--Hinton residual is also found to be multiplied by a geometric factor that arises from the flux-surface averaged classical polarization. Using the near-axis-expansion framework, we derive an analytic expression for , which varies significantly among different configurations. These analytic results are compared with numerical simulation results from the global gyrokinetic particle-in-cell code GTC, and good agreement with the theoretical Rosenbluth--Hinton residual level is achieved only when the quasisymmetry error is small enough. Since zonal flows can be important for regulating turbulent transport, these results suggest a possible relation between the transport level and the stellarator geometric parameters via nonlinear interactions with zonal flows.
References in corpus (19)
- Magnetic fields with precise quasisymmetry for plasma confinement
- Nonlinear dynamics of phase space zonal structures and energetic particle physics in fusion plasmas
- Energetic Consistency and Momentum Conservation in the Gyrokinetic Description of Tokamak Plasmas
- Direct construction of optimized stellarator shapes. I. Theory in cylindrical coordinates
- Constructing stellarators with quasisymmetry to high order
- Direct construction of optimized stellarator shapes. II. Numerical quasisymmetric solutions
- Necessary and Sufficient Conditions for Quasisymmetry
- Exact momentum conservation laws for the gyrokinetic Vlasov-Poisson equations
- Residual zonal flows in tokamaks and stellarators at arbitrary wavelengths
- Construction of Quasisymmetric Stellarators Using a Direct Coordinate Approach
- Phases and phase-transitions in quasisymmetric configuration space
- Constructing the space of quasisymmetric stellarators
- MHD stability and the effects of shaping: a near-axis view for tokamaks and quasisymmetric stellarators
- Tokamak elongation: how much is too much? II Numerical results
- Semianalytical calculation of the zonal-flow oscillation frequency in stellarators
- Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators
- Ion-temperature-gradient stability near the magnetic axis of quasisymmetric stellarators
- The residual flow in well-optimized stellarators
- Intrinsic toroidal rotation driven by turbulent and neoclassical processes in tokamak plasmas from global gyrokinetic simulations