Multi-plasmoid magnetic reconnection initiated by kinetic instabilities in colliding laser-produced plasmas*

Magnetic reconnection enables the explosive conversion of magnetic field energy to plasma kinetic energy in plasmas ranging from laboratory to astrophysical environments.  A challenge has been to understand how reconnection proceeds rapidly in large systems, though theory and simulations have shown reconnection rates to be greatly enhanced by plasmoid instabilities, which break a long current sheet into a hierarchy of shorter reconnection layers.  Here we show experiments with colliding magnetized laser-produced plasmas obtaining extended current sheets (L/d_i ~ 100, where d_i is the ion skin depth) and low dissipation (high Lundquist number S= μ₀LV_A/η ~ 1000).  The current sheet is observed to break up into a chain of a large number (~20) of magnetic islands.  Proton radiography and optical shadowgraphy observe the size and temporal growth of island structures, which merge into larger structures over the course of the interaction.  We discuss astrophysical implications of these observations and reconnection experiments at NIF at even larger system size.