Abstract Details
Abstracts
Author: Xu Chu
Requested Type: Poster
Submitted: 2024-04-12 12:18:12
Co-authors: S.C.Cowley, F.I.Parra
Contact Info:
Princeton Plasma Physics Laboratory/Princeton Univ
100 Stellarator Rd
Princeton, 08540
Mercer
Abstract Text:
We investigate the nonlinear MHD stability and saturation of ideal MHD ballooning modes. We assume that the nonlinear solution is an isolated flux tube that moves radially[1]. We extend previous results by Ham et al.[2]
on the stability and saturation of such flux tubes in tokamaks to stellarators.
Tools based on the DESC[3] equilibrium
solver were developed to calculate saturated states of perturbed flux tubes along with their energy in general stellarator equilibria.
Benchmarks against linear dynamics in both tokamaks and stellarators were performed.
Asymptotic analysis of flux tube behavior at large toroidal angle zeta shows that the flux tube displacement decays as zeta^nu, where nu is the same as the exponent calculated in the linear Mercier stability analysis. For our nonlinear model to be valid, nu <= -1 is required.
Systematic convergence analysis showed that the calculation of energy of a displaced flux tube is very sensitive to the force error of the numerical equilibrium.
First order contribution in energy due to force error makes the computed energy dependent on the simulation box size, even when the flux tube radial displacement calculation is converged. A modified algorithm for calculating energy of a flux tube by comparing neighbouring piece-wise C^1 flux tubes is proposed, which is shown to be much less sensitive to force error. Using the tools developed, nonlinear saturated flux tubes are calculated on multiple stellarators, including NCSX and ESTELL. Metastable saturated flux tube states can be found when the equilibrium is near linear ballooning marginal stablility.
References:
[1] S. C. Cowley, et. al., Proc. R. Soc. A 471, 20140913 (2015)
[2] C. J. Ham, et. al., Plasma Phys. Control. Fusion 60, 075017 (2018)
[3] D. Panici, et. al., J. Plasma Phys. 89, 955890303 (2023)
Comments: