VMEC Convergence Near the Magnetic Axis: Issues, Diagnosis, and Repair

POSTER

Abstract

The VMEC (Variational Moments Equilibrium Code) code is a non-axisymmetric MHD equilibrium code. It can compute both free-boundary and fixed-boundary equilibria, and is widely used for equilibrium reconstruction, stellarator design, and experimental planning and interpretation. Recent comparison of free-boundary zero-beta toroidal current-free equilibria with Biot-Savart field-line following have shown that some VMEC-computed physics properties near the magnetic axis converge slower than expected (with exponent ~ -1 instead of the expected -2) as the radial resolution is increased. Possible causes of this slow convergence, along with potential algorithm improvements will be explored.

*This work is funded in part by Auburn University, the U.S. DOE under contract DE-AC02-09CH11466 with PPPL, contract DE-AC05-00OR22725 with UT-Battelle, LLC, and grant DE-SC0023486 at the University of Montana.

Presenters

  • James D Hanson

    • Auburn University

Authors

  • James D Hanson

    • Auburn University

  • Mark R Cianciosa

    • Oak Ridge National Laboratory
    • Oak Ridge National Lab

  • Stuart R Hudson

    • Princeton Plasma Physics Laboratory

  • Jonathan Schilling

    • Proxima Fusion GmbH

  • John C Schmitt

    • Type One Energy
    • Auburn University, Type One Energy