The use of near-axis magnetic fields for stellarator turbulence simulations

@article{Jorge2020TheUO,
  title={The use of near-axis magnetic fields for stellarator turbulence simulations},
  author={Rogerio Jorge and Matt Landreman},
  journal={Plasma Physics and Controlled Fusion},
  year={2020},
  volume={63}
}
The design of turbulence optimized stellarators has so far relied on three-dimensional equilibrium codes such as VMEC in order to find the minimum of a given objective function. In this work, we propose a complimentary approach based on the near-axis expansion to compute the geometry parameters of neoclassicaly optimized stellarators used in turbulence studies. As shown here, the near-axis expansion can be a reasonable approximation of the geometric parameters relevant for turbulence and… 
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References

SHOWING 1-10 OF 59 REFERENCES
Magnetic well and Mercier stability of stellarators near the magnetic axis
We have recently demonstrated that by expanding in small distance from the magnetic axis compared with the major radius, stellarator shapes with low neoclassical transport can be generated
Ballooning modes in 3-D stellarators with shear
Pressure-driven ballooning and interchange instabilities in three-dimensional (3-D) vacuum Stellarator equilibria similar to those of the Heliotron-E device are investigated. The toroidal curvature
Direct construction of optimized stellarator shapes. Part 2. Numerical quasisymmetric solutions
Quasisymmetric stellarators are appealing intellectually and as fusion reactor candidates since the guiding-centre particle trajectories and neoclassical transport are isomorphic to those in a
TEM turbulence optimisation in stellarators
With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has
Construction of quasisymmetric stellarators using a direct coordinate approach
Optimized stellarator configurations and their analytical properties are obtained using a near-axis expansion approach. Such configurations are associated with good confinement as the guiding center
Three-dimensional analysis of tokamaks and stellarators
  • P. Garabedian
  • Physics
    Proceedings of the National Academy of Sciences
  • 2008
TLDR
Three-dimensional asymmetries in bifurcated numerical solutions of the axially symmetric tokamak problem are relevant to the observation of unstable neoclassical tearing modes and edge localized modes in experiments.
Near-axis expansion of stellarator equilibrium at arbitrary order in the distance to the axis
A direct construction of equilibrium magnetic fields with toroidal topology at arbitrary order in the distance from the magnetic axis is carried out, yielding an analytical framework able to explore
Controlling turbulence in present and future stellarators.
TLDR
This work derives the first turbulence-optimized stellarator configuration stemming from an existing quasiomnigenous design using a stochastic global-search optimization method.
Stellarators with the magnetic symmetry of a tokamak
To meet the requirements of the U.S. Stellarator Power Plant Study, a Modular Helias‐like Heliac (MHH) configuration was developed that has features in common with a quasihelically symmetric
Electron temperature gradient driven turbulence
Collisionless electron-temperature-gradient-driven (ETG) turbulence in toroidal geometry is studied via nonlinear numerical simulations. To this aim, two massively parallel, fully gyrokinetic Vlasov
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