Universal asymptotical behaviour of poloidal spectra of resonant magnetic perturbations created by a set of saddle coils in tokamaks

摘要

Universal asymptotical behaviour of poloidal spectra of resonant magnetic perturbations created by a set of saddle coils in tokamak plasmas is studied in a vacuum approximation. It is shown that the poloidal mode spectra for a given toroidal mode can be presented by a linear combination of three universal asymptotical formulae corresponding to horizontal and vertical segments of a set of saddle coils. Each of the asymptotical formulae depends only on the safety factor of the equilibrium plasma and the geometry of the perturbation coils. The validity of the universal formulae is confirmed by numerical computations of the poloidal mode spectra for typical plasmas with large and small inverse aspect ratios, DIII-D-like plasmas with internal (I-) coils (Jackson et al 2003 Proc. 30th EPS Conf. on Controlled Fusion and Plasma Physics (St Petersburg, Russia, 7-11 July 2003) vol 27A (ECA) P-4.47) and spherical NSTX-like plasmas with error field coils (Gates et al 2009 Nucl. Fusion 49 104016).