  We introduce a topology optimization method to design permanent magnets for
advanced stellarators. Recent researches show that permanent magnets have great
potentials to simplify stellarator coils. We adopt state-of-the-art numerical
techniques to determine the presence of magnets in the entire designing space.
The FAMUS code is developed and it can design engineering-feasible permanent
magnets for general stellarators satisfying the constraints of the maximum
material magnetization and explicitly forbidden regions. FAMUS has been
successfully verified against the previously proposed linear method. Three
different permanent magnet designs together with planar TF coils for a
half-Tesla NCSX configuration have been obtained for demonstrations. The
designs have good accuracy in generating the desired equilibrium and offer
considerably large plasma access on the outboard side. The results show that
FAMUS is a flexible, advanced numerical tool for future permanent magnet
stellarator designs.
