Ion-temperature-gradient stability near the magnetic axis of quasisymmetric stellarators

Abstract

The stability of the ion-temperature gradient mode in quasisymmetric stellarators is assessed. This is performed using a set of analytical estimates together with linear gyrokinetic simulations. The peak growth rates, their corresponding real frequencies and wave-vectors are identified. A comparison is made between a first-order near-axis expansion model and eleven realistic designs obtained using numerical optimization methods. It is found that while the near-axis expansion is able to replicate the growth rates, real frequencies and perpendicular wave-vector at the inner core (both using simplified dispersion relations and first-principle gyrokinetic simulations), it leads to an overestimation of the growth rate at larger radii. An approximate analytic solution of the ITG dispersion relation for the non-resonant limit suggests growth rates could be systematically higher in quasi-axisymmetric (QA) configurations compared to quasi-helically (QH) symmetric ones. However except for very close to the axis, linear gyrokinetic simulations do not show systematic differences between QA and QH configurations.

References in corpus (14)

• Astrophysical Gyrokinetics: Basic Equations and Linear Theory
• Properties of a new quasi-axisymmetric configuration
• Direct construction of optimized stellarator shapes. I. Theory in cylindrical coordinates
• Constructing stellarators with quasisymmetry to high order
• Collisionless microinstabilities in stellarators III - the ion-temperature-gradient mode
• Direct construction of optimized stellarator shapes. II. Numerical quasisymmetric solutions
• Collisionless microinstabilities in stellarators I - analytical theory of trapped-particle modes
• $\text{stella}$: a mixed implicit-explicit, delta-f gyrokinetic code for general magnetic field configurations
• Near-Axis Expansion of Stellarator Equilibrium at Arbitrary Order in the Distance to the Axis
• Simulating Gyrokinetic Microinstabilities in Stellarator Geometry with GS2
• Construction of Quasisymmetric Stellarators Using a Direct Coordinate Approach
• The Parallel Boundary Condition for Turbulence Simulations in Low Magnetic Shear Devices
• The Use of Near-Axis Magnetic Fields for Stellarator Turbulence Simulations
• Optimized quasisymmetric stellarators are consistent with the Garren-Boozer construction

Cited by in corpus (5)

• Critical gradient turbulence optimization toward a compact stellarator reactor concept
• Coarse-grained gyrokinetics for the critical ion temperature gradient in stellarators
• Calculating the linear critical gradient for the ion-temperature-gradient mode in magnetically confined plasmas
• Collisionless zonal-flow dynamics in quasisymmetric stellarators
• Energetic Particle Tracing in Optimized Quasisymmetric Stellarator Equilibria