Authors: Dipanwita Misra(Graduate Student at West Virginia University), Dr. Giulia Murtas(Assistant Professor, Center for KINETIC Plasma Physics, West Virginia University)

Current sheet collapse is a fundamental process in the solar atmosphere, preceding magnetic energy release in both coronal and chromospheric environments. We investigate the nonlinear evolution of a one-dimensional resistive MHD Harris current sheet, subjected to an externally imposed converging flow following the framework of Takeshige et al. 

The Lorentz force drives rapid current-sheet thinning, producing a sharp increase in peak current density and strong magnetic compression. As the collapse proceeds, a density depletion develops at the sheet center while plasma and magnetic flux are expelled outward. This evolution naturally transitions into a magnetic-piston phase in which the compressed current sheet launches a pair of fast magnetosonic shocks propagating symmetrically away from the reconnection region. We see a shock emerge approximately after (t~0.06TA) and propagates at a speed of nearly (VSh ~0.99VA) in the laboratory frame. Rankine–Hugoniot analysis in the shock rest frame yields a fast-mode Mach number (Mf ~2.3) and magnetic compression ratio (B2/B1 ~2.4), consistent with theoretical expectations for perpendicular MHD shocks (Vršnak & Lulić 2000).

These results establish a quantitative MHD baseline for ongoing studies incorporating partial ionisation, including ion–neutral collisions, ionisation, and recombination, to determine how two-fluid effects modify shock formation, propagation, compression, and energy partition in chromospheric plasmas.