Proton Imaging of Diamagnetic Cavity Formation in Expanding Laser-Driven Plasma at the OMEGA Laser Facility

In this work, we present experiments conducted at the OMEGA laser facility to investigate the collimation of magnetized plasma outflows resulting from a diamagnetic cavity. A 1-ns, 4.5-kJ laser pulse was used to irradiate one side of CH and zinc planar target, producing an expanding plasma plume from the rear surface. A uniform external magnetic field of 20 T was applied using a pair of Helmholtz coils. Synthetic proton radiography at 20 ns, produced based on FLASH simulations, pending experimental validation, shows a region of reduced magnetic field within the plume relative to the background field, consistent with the formation of a diamagnetic cavity. In the solar context, high-speed plasma jets—considered potential contributors to the solar wind—are observed to propagate along open magnetic field lines in coronal holes. These jets are strongly collimated by magnetic pressure, with typical widths of ~100 km and lengths of several megameters, likely due to the presence of an internal diamagnetic cavity.