The Current Status and Future of the SIESTA Equilibrium Code

Abstract

The SIESTA magnetohydrodynamic equilibrium code is used to nd a stable plasma equilibrium in toroidal devices such as stellarators and tokamaks. Previous equilibrium codes, such as VMEC, did not allow magnetic surfaces to tear and thus only resolved con gurations with closed, nested ux surfaces. SIESTA uses a static, background co- ordinate system and includes resistivity, allowing current sheets to open into magnetic islands. Through a nonlinear energy minimization process, SIESTA nds a stable, lower-energy equilibrium if the initial starting equilibrium is unstable to perturbations applied at rational surfaces. The code is introduced, followed by a discussion of the research done on and problems found with a pentadiagonal solver. An initial study of a nullspace inherent to the problem is presented next, followed by some post-processing results studying the structure of magnetic islands.