A dual-Helmholtz-coil magnetic field system for polarized ³He

This study focuses on developing a dual-Helmholtz-coil magnetic field system for polarized ³He to generate a uniform magnetic field. A theoretical analysis of the mechanism by which dual Helmholtz coils produce a uniform magnetic field was first conducted. Based on these findings, the magnetic device was designed with the finite element analysis software COMSOL, employing an optimization algorithm to efficiently set current densities and minimize the transverse gradient in the central region. The simulated transverse gradient achieved was 9.54 × 10⁻⁵ cm⁻¹ in the 20 cm × 20 cm × 8 cm central region, and the experimental measurement yielded a value of 6.31 × 10⁻⁴ cm⁻¹. Additionally, lifetime testing of two polarized ³He cells revealed lifetimes of 151.0 ± 1.8 h and 206.2 ± 4.4 h, demonstrating the excellent magnetic field uniformity of the device. The current work integrates theoretical, simulated, and experimental results. It advances polarized ³He magnetic technology, offers an upgrade solution for off situ polarized ³He pumping stations to extend the volume of the uniform magnetic field without enlarging the coil size, and provides a method for using polarized ³He on neutron beamlines requiring large acceptance angles.