Laboratory Astrophysics Experiments of Collisionless Shock by Supersonic Collision of Plasmoids

Abstract

Shock waves in space, considered as an acceleration mechanism of cosmic rays, are vital physical phenomena. Collisionless shock waves, generated in space plasma without particle collisions but through electromagnetic fields, remain a complex and critical research topic in astronomy and plasma physics. Hindered by the difficulty of direct observation, uncovering their mechanisms requires replicating these shock waves in laboratories to simultaneously observe local and macroscopic behaviors. Our experiment forms plasmoids with extremely high beta values (plasma pressure/magnetic pressure ～ 100%), similar to space conditions. In the presented experiments, a set of two plasmoids are generated using two conical theta-pinch formation sections and they are collided at the relative velocity of 100–600 km/s, exceeding the sound and Alfvén speeds. This process formed meter-scale collisionless shock waves, allowing for direct imaging and internal electromagnetic field measurements. This experimental approach opens new method to investigate a key process in astrophysics.