Finite-beta equilibria for Wendelstein 7-X configurations using the Princeton Iterative Equilibrium Solver code

Fixed- and free-boundary equilibria for Wendelstein 7-X (W7-X) [W. Lotz et al., Plasma Physics and Controlled Nuclear Fusion Research 1990 (Proc. 13th Int. Conf. Washington, DC, 1990), (International Atomic Energy Agency, Vie nna, 1991), Vol. 2, p. 603] configurations are calculated using the Princet on Iterative Equilibrium Solver (PIES) [A. H. Reiman et al., Comput. Phys. Commun., 43, 157 (1986)] to deal with magnetic islands and stochastic regio ns. Usually, these W7-X configurations require a large number of iterations for PIES convergence. Here, two methods have been successfully tested in a n attempt to decrease the number of iterations needed for convergence. Firs t, periodic sequences of different blending parameters are used. Second, th e initial guess is vastly improved by using results of the Variational Mome nts Equilibrium Code (VMEC) [S. P. Hirshmann et al., Phys. Fluids 26, 3553 (1983)]. Use of these two methods have allowed verification of the Hamada c ondition and tendency of "self-healing'' of islands has been observed. (C) 1999 American Institute of Physics. [S1070-664X(99)03503-X].