Experimental verification of Petschek’s double shock structure in a two-fluid magnetic reconnection layer*

Petschek reconnection layer model has been very popular to explain a fast reconnection by MHD theory. But its theoretical interpretation has been rather controversial.  In a prototypical two-dimensional antiparallel reconnection geometry, we experimentally verify the well- known Petshek-type reconnection layer (1) of double wedge structure and explain by two-fluid dynamics. In a two-fluid reconnection layer, as electrons and ions move into the reconnection layer with different paths, the magnetized electrons penetrate deep into the reconnection layer generating a strong potential well in the diffusion region. The shape of the well expands towards the exit of exhaust region (2). A sharp current layer develops at the separatrix region generating abrupt changes of magnetic field vectors. Magnetic field energy is converted to electric field potential energy through the motion of magnetized electrons in the background of non-magnetized ions. While some of the magnetic energy is deposited to the electrons in the electron-diffusion layer, ions gain substantial energy through electrostatic acceleration across the potential well in the broader ion diffusion region. The Petschek-type double shock structure is formed (3) and can be explained by the two-fluid dynamics of the reconnection layer around the electron diffusion region.

(1) H. Petschek,  NASA Spec. Pub.50, 425 (1964),

(2) M. Yamada et al, Phys. Plasmas 23, 055402 (2016),

(3) J. Yoo and M. Yamada, to be published (2024)