Analysis of the Last Closed Magnetic Surface and Edge Topology for the STAR_Lite Stellarator

The magnetic confinement of plasma in stellarators relies on nested magnetic surfaces, whose breakdown near the edge defines divertors that channel plasma exhaust out of the device. Hampton University is constructing a university-scale modular stellarator (R=0.5 m, |B|≈0.1 T), STAR_Lite, to experimentally study edge magnetic surfaces and their resilience to field errors. This project develops an open-source Python code for modeling edge topology using a stellarator magnetic field Hamiltonian [Boozer & Punjabi, Phys. Plasmas 25, 092505 (2018)]. We verify Poincaré sections of field lines in the model Hamiltonian by comparison with existing computational results. Understanding the last closed magnetic surface is implemented by Poincaré section calculations via parallel computing with SciPy and a numba-accelerated Newton solver. We then apply a Gaussian-window Fourier transform of field-line trajectories to study surface breakdown using far shorter field line integrations than Poincaré sections. The method's efficiency and resolution address limitations in vacuum vessel wall and magnetic surface separation and integration step size, providing a versatile tool for divertor design, optimization, and edge physics in stellarators.