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Laboratory dipole confinement was proposed by Hasegawa in 1987 as a possible route to fusion-relevant plasmas and has been explored in levitated-dipole experiments such as LDX, RT-1, and the recent Junior device. A dipole magnetic field is characterized by its strong magnetic-flux expansion, i.e., the magnetic field strength varies strongly along a field line, which poses challenges for numerical simulations. In this work, we use Hermes-3 to study three-dimensional plasma dynamics near the edge of a dipole-confined plasma.
Fluctuations in the closed-field-line region in dipole-confined plasmas are often believed to be flute-like with $k_\parallel\approx 0$. We find that this picture can break down near a marginal stationary profile. In slightly supercritical profiles, three-dimensional simulations reveal that non-flute fluctuations with finite parallel structure naturally emerge due to the strong variation of the local magnetic geometry along the field line. Furthermore, these fluctuations produce a differential radial transport: along the same field line, particles are pinched inward near the outer midplane while being driven outward near the inner midplane. This poloidal-angle-dependent transport is not captured by purely flute-like, flux-tube-averaged descriptions. This result is further supported by eigenmode solutions from a simplified drift-reduced fluid model, whose quasilinear flux reproduces the differential radial transport. Future work will extend the simulation domain to include the X-point and open-field-line regions in a dipole field.