AEGIS: An adaptive ideal-magnetohydrodynamics shooting code for axisymmetric plasma stability

A new linear ideal-magnetohydrodynamics stability code for axisymmetric plasmas, AEGIS, is described. The AEGIS code employs adaptive shooting in the radial direction and Fourier decomposition in the poloidal direction. The general solution is a linear combination of the independent solutions of the Euler–Lagrange equations solved by the adaptive shooting. A multiple-region matching technique is used to overcome the numerical difficulty associated with the stiff nature of the independent solutions. Benchmarks with other MHD codes show good agreement. Because it is adaptive, the AEGIS code has very good resolution near the singular surfaces of MHD modes. AEGIS has the additional advantage of allowing the investigation of modes with not only low mode numbers, but also intermediate to high mode numbers.