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Author: Alan H Glasser
Requested Type: Poster
Submitted: 2017-03-13 14:16:20

Co-authors: J.-K. Park

Contact Info:
Fusion Theory & Computation, Inc.
24062 Seatter Lane NE
Kingston, WA   98346
USA

Abstract Text:
We report the development of a new version of DCON for nonaxisymmetric toroidal plasmas, e.g. stellarators. The DCON code is widely used for fast and accurate determination of ideal MHD stability of axisymmetric toroidal plasmas. Minimization of the ideal MHD energy principle W is reduced to adaptive numerical integration of a coupled set of ordinary differential equations for the complex poloidal Fourier harmonics of the perturbed normal displacement. For a periodic cylindrical plasma, both the poloidal and toroidal coordinates are ignorable, allowing for treatment of single harmonics m and n. For an axisymmetric toroidal plasma, poloidal symmetry is broken, causing different m’s to couple and requiring simultaneous treatment of M harmonics. For a nonaxisymmetric plasma, toroidal symmetry is also broken, causing different n’s to couple and requiring treatment of N harmonics. For a stellarator with field period l, e.g. l = 5 for W7X, each toroidal harmonic n is coupled to toroidal harmonics n+k*l, for all integers k. Both M and N are truncated on the basis of convergence. Singular surfaces occur at all values of safety factor q = m/n in the plasma. The DCON equations have been generalized to allow for multiple n’s with coupling matrices F, K, and G. An interface has been developed for the nonaxisymmetric equilibrium code VMEC, which provides values for these matrices. Their Fourier harmonics are fit to cubic splines as a function of the radial coordinate s, allowing for adaptive integration of the ODEs. The status of the code development will be presented.

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