Computational Study of Error-field Effects on W7-X Stellarator Equilibria

摘要

1 Introduction The Wendelstein 7-X (W7-X, [1]) stellarator currently under construction [2] in Greifswald, Germany, has been designed to operate in a low-shear rotational transform regime around unity, which is relatively free from Iow-order rationals. As an important part of the W7-X divertor concept, the main operation scenarios will have the 5/m, m = 4,5,6 island chains inherent to the five-periodic stellarator in their respective plasma edge regions. With the presence or vicinity of the low-order rational ι = 1, however, possible magnetic error fields can destroy the periodicity of the stellarator field and, thus, hamper plasma performance. The impact of error-fields on the W7-X high-ι variant with ι≈ l near the magnetic axis and ι≈ 5/4 near the plasma edge is studied here. As a first application, m = 1 field perturbations are considered which retain the five-fold periodicity of the plasma, but dislocate the magnetic axis. With the perturbed-equilibrium method [3], an approach alternative to standard equilibrium calculations, as done with VMEC [4] or PIES [5]), was developed to computationally assess the impact of such error fields on stellarator equilibria [6].