Optimization of stellarator configurations combining omnigenity and piecewise omnigenity

Abstract We present a method for optimizing stellarator configurations that combine omnigenity and piecewise omnigenity (pwO). Within the OOPS optimization framework (Liu et al 2025 2502.09350 ), we introduce a mapping technique that can ‘squeeze’ general omnigenous fields to approximate pwO on the high-field side. Using this approach, we obtain a range of optimized configurations that combine poloidal omnigenity (PO) and pwO, spanning different field periods and aspect ratios. We further show that these configurations are compatible with a magnetic well. The resulting configurations exhibit favorable neoclassical transport and bootstrap current properties while partially relaxing the strict constraints of omnigenity. These results suggest that such configurations are promising candidates for future stellarator reactors.