Evolution and Breakup of Current Sheets in Laser-Driven Magnetic Reconnection*

Magnetic reconnection is a fundamental plasma process in which opposing magnetic fields lines annihilate and rearrange, releasing magnetic energy through plasma flows and heating the plasma in a current sheet. This process drives several astrophysical processes including solar and stellar flares. In this study, we present high-fidelity measurements of the current sheet evolution and breakup between colliding, magnetized plasma plumes in a laser-driven magnetic reconnection experiment. The magnetic fields are measured with a hybrid scheme of proton radiography that uses both mesh and fluence-based methods; the fields in the current sheet are inverted from the proton fluence while the non-reconnecting fields are measured using mesh deflectometry. The mesh measurements contribute to the fluence inversion by providing boundary conditions and constraining the source proton profile [1], which significantly improves the accuracy of the inversion. Using this methodology, we obtain magnetic measurements over the entire radiograph domain, enabling an estimate of the reconnection rate. Additionally, the current sheet develops large current density fluctuations (~50-100%) which we term current sheet breakup, and we compare to relevant instabilities including classical tearing with kinetic contributions.