Tomographic characterization of self-generated magnetic fields in laser-produced plasmas

Strong magnetic fields (>30 T) are commonly self-generated in plasmas produced from high-power lasers through the Biermann-battery mechanism, which arises when electron density and temperature gradients are not co-linear (∇n_e × ∇T_e). These fields naturally occur in laser-solid interactions, enabling laboratory studies of astrophysical processes and modifying plasma transport relevant for inertial confinement fusion (ICF). However, there are several open questions surrounding magnetic field generation and transport in laser-produced plasmas, partially due to incomplete experimental characterization. In this work, we characterize the full three-dimensional magnetic fields generated from a laser-solid interaction using multi-view proton radiography on the OMEGA laser. Proton backlighters from four distinct positions were used in successive shots to image the magnetic fields. The different view angles break the degeneracy of the path-integrated diagnostic and enable a tomographic inversion of the fields. In each view angle, an advanced scheme of mesh proton radiography with x-ray fiducials measures absolute proton deflection. We infer magnetic fields extending into the high temperature, rarefied corona that are sufficient to strongly magnetize the plasma (ω_ce𝜏_ei ≫ 1) and significantly modify electron heat transport. Comparison with extended MHD simulations suggest that magnetic fields are suppressed near the target foil due to nonlocal effects but remain unsuppressed in the corona where stronger magnetization localizes the transport. This finding is intimately related to indirect drive ICF where increased magnetization of the hohlraum plasma could alter global plasma properties and influence processes like implosion symmetry. This study is the first demonstration of a tomographic inversion of proton radiography, providing a valuable tool to resolve open questions surrounding magnetic field structure and dynamics in magnetized high-energy-density plasmas.