Background In indirect-drive inertial confinement fusion(ICF), self-generated magnetic fields near the inner wall of a gold hohlraum affect electron thermal conduction, potentially altering the electron temperature distribution and laser propagation. This issue is of significant interest in the ICF community; however, experimental data on self-generated magnetic fields in laser-Au target interactions remain scarce.

Purpose The aim is to obtain the distribution of self-generated magnetic fields adjacent to an Au target surface, thereby providing benchmark data for validating radiation magnetohydrodynamic simulations.

Methods Experiments were conducted on the SG-II Upgrade facility. A 3 ns, frequency-tripled high-power laser was incident on a planar Au target to generate self-generated magnetic fields. A picosecond-laser-driven proton beam was employed to radiograph the magnetic fields. The field distribution was reconstructed using the PROBLEM code. The experimental process was simulated with the FLASH magnetohydrodynamic(MHD) code to elucidate the underlying physical mechanisms.

Results A distinct umbrella-shaped proton dose distribution was obtained. The reconstructed path-integrated magnetic field strength was approximately 16 T·mm, consistent with the results of two-dimensional FLASH simulations. Simulations indicate that the magnetic field modifies the electron temperature distribution by restricting thermal conduction. Near the critical density surface, the magnetic field shifts the high-temperature region closer to the target surface. In the peripheral region of the focal spot, the Hall coefficient \chi is approximately 10, indicating severely inhibited electron thermal conduction, which results in a reduction of the electron temperature by approximately 1 keV away from the focal spot. The Nernst effect is primarily observed in regions of high temperature gradient in the trailing part of the laser propagation. The magnetic field is transported toward lower temperatures with an average Nernst velocity \overline\upsilon _N of approximately 17 km/s. During this transport, the magnetic field strength increases from 20 T to 50 T, and electron thermal conduction follows the transported field. Magnetic diffusion predominantly occurs in the electron ablation region near the critical density surface, characterized by low temperature and high density, where the magnetic field is strongly dissipated. When the diffusion term is omitted, the simulated magnetic field strength increases by a factor of tens, yielding unphysical spike structures.

Conclusions This study provides high-quality proton radiography data for validating magnetohydrodynamic simulations and offers valuable insights into the generation mechanisms and effects of self-generated magnetic fields near gold hohlraum walls under ICF conditions.