The shear Alfvén continuum of quasisymmetric stellarators

Abstract

The shear Alfvén wave (SAW) continuum plays a critical role in the stability of energetic particle-driven Alfvén eigenmodes. We develop a theoretical framework to analyze the SAW continuum in three-dimensional quasisymmetric magnetic fields, focusing on its implications for stellarator design. By employing a near-axis model and degenerate perturbation theory, the continuum equation is solved, highlighting unique features in 3D configurations, such as the interactions between spectral gaps. Numerical examples validate the theory, demonstrating the impact of flux surface shaping and quasisymmetric field properties on continuum structure. The results provide insights into optimizing stellarator configurations to minimize resonance-driven losses of energetic particles. This work establishes a basis for incorporating Alfvénic stability considerations into the stellarator design process, demonstrated through optimization of a quasihelical configuration to avoid high-frequency spectral gaps.

References in corpus (11)

• The Kernel Polynomial Method
• Necessary and Sufficient Conditions for Quasisymmetry
• Mapping the space of quasisymmetric stellarators using optimized near-axis expansion
• Near-Axis Expansion of Stellarator Equilibrium at Arbitrary Order in the Distance to the Axis
• Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry
• Constructing the space of quasisymmetric stellarators
• MHD stability and the effects of shaping: a near-axis view for tokamaks and quasisymmetric stellarators
• Study of the Alfven Eigenmodes stability in CFQS plasma using a Landau closure model
• Optimized quasisymmetric stellarators are consistent with the Garren-Boozer construction
• Exploration of the parameter space of quasisymmetric stellarator vacuum fields through adjoint optimisation
• Collisionless zonal-flow dynamics in quasisymmetric stellarators