Enhanced preconditioner for JOREK MHD solver

The JOREK extended magneto-hydrodynamic (MHD) code is a widely used simulation for studying the non-linear dynamics of large-scale instabilities in divertor tokamak plasmas. Due to large scale-separation intrinsic these phenomena both space and time, computational costs simulations realistic geometry with parameters can be very high, motivating investment considerable effort optimization. In this article, set developments regarding solver preconditioner described, which lead overall significant benefits production simulations. This comprises particular enhanced convergence highly scenarios general reduction memory consumption costs. include faster construction matrices, domain decomposition preconditioning matrices libraries that handle distributed interfaces additional libraries, an option use matrix compression methods, implementation complex interface preconditioner. most development presented consists generalization physics based "mode groups", allows account dominant interactions between toroidal Fourier modes At cost moderate increase consumption, technique strongly enhance suitable cases allowing significantly larger time steps. For all developments, benchmarks on typical demonstrate resulting improvements.