The ISLAND module for computing magnetic island widths in tokamaks

The ISLAND module in the National Transport Code Collaboration (NTCC) Module Library computes the saturated widths of multiple magnetic islands due to neoclassical tearing modes by implementing a quasi-linear model that includes the effects of arbitrary aspect ratio, cross-sectional shape, and plasma beta. This paper presents a significantly improved version of the module available at the NTCC Library. The model was updated to include the distortion of islands caused by the radial variation of the perturbed magnetic field near the mode rational surface. The computer algorithm implemented by the module was redesigned to increase its speed, reliability and accuracy. The new module has been successfully interfaced with the BALDUR integrated modeling code, where it is used to compute the saturated widths of multiple islands in tokamak discharges.