A family of quasiaxisymmetric stellarators with varied rotational transform
Abstract
We apply a continuation method to recently optimized stellarator equilibria with excellent quasiaxisymmetry (QA) to generate new equilibria with a wide range of rotational transform profiles. Using these equilibria, we investigate how the rotational transform affects fastparticle confinement, the maximum coilplasma distance, the maximum growth rate in linear gyrokinetic iontemperature gradient (ITG) simulations, and the ion heat flux in corresponding nonlinear simulations. We find values of twoterm quasisymmetry error comparable to or lower than the similar LandremanPaul (Phys. Rev. Lett. 128, 035001) configuration for values of the mean rotational transform $\bar{\iota}$ between $0.12$ and $0.75$. The fastparticle confinement improves with $\bar{\iota}$ until $\bar{\iota} = 0.73$, at which point the degradation in quasisymmetry outweighs the benefits of further increasing $\bar{\iota}$. The required coilplasma distance only varies by about $\pm 10\%$ for the configurations under consideration, and is between $2.8\,\mathrm{m}$ to $3.3\,\mathrm{m}$ when the configuration is scaled up to reactor size. The maximum growth rate from linear gyrokinetic simulations increases with $\bar{\iota}$, but also shifts towards higher $k_y$ values. The maximum linear growth rate is sensitive to the choice of flux tube at rational $\iota$, but this can be compensated for by taking the maximum over several flux tubes. The corresponding ion heat fluxes from nonlinear simulations display a nonmonotonic relation to $\iota$. Sufficiently large positive shear is destabilizing. This is reflected both in linear growth rates and nonlinear heat fluxes.
 Publication:

arXiv eprints
 Pub Date:
 January 2024
 DOI:
 10.48550/arXiv.2401.09021
 arXiv:
 arXiv:2401.09021
 Bibcode:
 2024arXiv240109021B
 Keywords:

 Physics  Plasma Physics
 EPrint:
 20 pages, 15 figures